| 65 sujets IRFU |
Dernière mise à jour : 29-07-2021
Measuring the Higgs-top coupling CP properties in the multilepton channel at the ATLAS experiment
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Starting date : 01-10-2021
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The proposed PhD is aiming at measuring the CP properties of the Higgs-top coupling in the multilepton channel within the ATLAS experiment. Discovering new sources of CP violation is one of the most pressing questions in particle physics today. The Yukawa-like interactions in the Higgs boson sector could provide a particularly attractive way for additional sources of CP violation. The goal of PhD is to measure the ttH process in two innovative ways. First new reconstruction algorithms to identify the heavy particles in ttH events will be developed, which is made very challenging by the multilepton final state. Then the analysis will be designed exclusively based on pure CP observables. New observables based on ratios or angles will be explored, and measurements in regions of phase space where the separation between the various Higgs-top processes is less dependent on the CP properties of the Higgs-top-quark coupling will be studied. This new analysis should also have increased sensitivity to other rarer top quark associated Higgs production modes such as tHq.
Probing new sources of CP violation in the Universe using Higgs boson production at the LHC
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Starting date : 01-10-2021
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The proposed PhD is aiming at probing new sources of CP violation in the Universe by studying the Higgs boson properties at the LHC, in particular through a modification of the coupling of the Higgs boson with the heaviest elementary particle: the top quark. The goal of this PhD is to develop a new data analysis strategy within the ATLAS collaboration probing the CP properties of the ttH coupling in pp collisions. The idea would be to design an analysis based exclusively on pure CP observables, meant to complement the existing model-dependent approach relying on machine learning methods that mix observables specific and non-specific to CP.
This new analysis should also have increased sensitivity to other rarer top quark associated Higgs production modes such as tHq.
New observables that will need to be developed will be made flexible enough to be applicable to a large panel of Higgs and top-quark decay channels. They will first be tested on the multilepton channel. A focus will be put on the reconstruction of the heavy particles (Higgs and top quark) in the final state, which is quite challenging in this channel.
This new analysis should also have increased sensitivity to other rarer top quark associated Higgs production modes such as tHq.
New observables that will need to be developed will be made flexible enough to be applicable to a large panel of Higgs and top-quark decay channels. They will first be tested on the multilepton channel. A focus will be put on the reconstruction of the heavy particles (Higgs and top quark) in the final state, which is quite challenging in this channel.
Weak-gravitational lensing mass maps for cosmology and gravitational wave astronomy
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Starting date : 01-09-2021
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Personal web page : http://www.cosmostat.org/jobs/mk_wlcosmogw_2020
Laboratory link : http://www.cosmostat.org
Weak lensing denotes galaxy image distortions induced by structures on large scales. Dark-matter maps obtained from weak lensing help us to shed light on the mystery of the recent acceleration of the Universe. In addition, they are important for gravitational waves (GW), which can be magnified by dark matter along the line of sight.
This PhD thesis will develop methods to analyse weak-lensing data. Machine-learning techniques will be used to calibrate the measurements. These methods will be applied to survey UNIONS (Ultraviolet Near-Infrared Optical Northen Sky Survey), and WFST (Wide-Field Survey Telescope), which will be built in China. The goal is to measure the properties of dark energy, and to correct magnification of GW signals.
This PhD thesis will develop methods to analyse weak-lensing data. Machine-learning techniques will be used to calibrate the measurements. These methods will be applied to survey UNIONS (Ultraviolet Near-Infrared Optical Northen Sky Survey), and WFST (Wide-Field Survey Telescope), which will be built in China. The goal is to measure the properties of dark energy, and to correct magnification of GW signals.
"3x2pt" analysis: Cross-correlations of cosmological probes, and application to state-of-the-art weak-lensing and galaxy clustering surveys
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Starting date : 01-09-2021
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Personal web page : http://www.cosmostat.org/jobs/mk_3x2pt_2020
Laboratory link : http://www.cosmostat.org/
The large upcoming cosmological experiments such as the space telescopes Euclid and Nancy Grace Roman, or the ground-based survey LSST, will use two main probes with the goal to measure the properties of dark matter and dark energy: weak gravitational lensing, which is the deformation of the images of distant galaxies by tidal fields on very large scales, and galaxy clustering, denoting the distribution of galaxies in the cosmic web.
This PhD thesis will explore the cross-correlation between those two probes, which is of great importance since these observables are sensitive to the same structures, which interrelates them. This work will be applied to data from the surveys UNIONS and DESI. The student will be trained at the interface between theory and observations, and provide key tools for upcoming large surveys.
This PhD thesis will explore the cross-correlation between those two probes, which is of great importance since these observables are sensitive to the same structures, which interrelates them. This work will be applied to data from the surveys UNIONS and DESI. The student will be trained at the interface between theory and observations, and provide key tools for upcoming large surveys.
Optimization of the booster for the electron-positron collider FCC-ee
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Starting date : 01-11-2020
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Laboratory link : http://irfu.cea.fr/dacm/
More : https://home.cern/science/accelerators/future-circular-collider
Currently, one of the burning questions in particle physics is the understanding of the mass origin of the particles by exploring Higgs properties, more specifically its self-interaction. An electron-positron collider is then a powerful tool for precision physics. In this purpose, the project "Future Circular Collider Innovation Study" (FCCIS) aims to deliver a conceptual report and to give a sustainable implementation long-term plan for a 1OO-km-long electron-antielectron collider at CERN.
The PhD student will join an international collaboration with CERN, DESY, INFN or KIT. The PhD will focus on the booster, the ring which accelerates electrons up to nominal energy before injecting into the collider. The main challenges of the booster are
i) the injection energy. The PhD student will determine the optimum injection energy of the booster ; this choice will have a great impact on the injection complex and its cost
ii) the booster optics. the PhD student will have to explore different optics and propose innovative solutions to improve and boost equilibrium conditions.
iii) the injection into the collider. The PhD student will study how to inject into the ring and will design the transfer lines up to the collider.
The PhD student will use the MAD-X code for the optics calculations, a reference code developed at CERN.
The PhD student will join an international collaboration with CERN, DESY, INFN or KIT. The PhD will focus on the booster, the ring which accelerates electrons up to nominal energy before injecting into the collider. The main challenges of the booster are
i) the injection energy. The PhD student will determine the optimum injection energy of the booster ; this choice will have a great impact on the injection complex and its cost
ii) the booster optics. the PhD student will have to explore different optics and propose innovative solutions to improve and boost equilibrium conditions.
iii) the injection into the collider. The PhD student will study how to inject into the ring and will design the transfer lines up to the collider.
The PhD student will use the MAD-X code for the optics calculations, a reference code developed at CERN.
ADVANCED AND ARTIFICIAL INTELLIGENCE TECHNIQUES TO MITIGATE LINEAR AND NON-LINEAR IMPERFECTIONS IN FUTURE CIRCULAR COLLIDERS
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Starting date : 01-10-2021
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Personal web page : http://dalena.web.cern.ch/dalena/
Laboratory link : http://irfu.cea.fr/dacm/index.php
After the discovery of the Higgs boson at the LHC, particle physics community is exploring and proposing next accelerators, to address the remaining open questions on the underlying mechanisms and on the constituents of the present universe. One of the studied possibilities is FCC (Future Circular Collider), a 100-km-long collider at CERN. The hadron version of FCC (FCC-hh) seems to be the only approach to reach energy levels far beyond the range of the LHC, in the coming decades, providing direct access to new particles with masses up to tens of TeV. The electron version of FCC brings a tremendous increase of production rates for phenomena in the sub-TeV mass range, making precision physics studies possible. A first study has shown no major showstopper in the colliders’ feasibility but has identified several specific challenges for the beam dynamics: large circumference (civil engineering constraints), beam stability with high current, the small geometric emittance, unprecedented collision energy and luminosity, the huge amount of energy stored in the beam, large synchrotron radiation power, plus the injection scenarios. This thesis will focus on the optimization of the hadron option of the future circular collider against linear and non-linear imperfections (i.e. magnets alignments and their field quality). A key point of this thesis is the comparison of current advanced correction schemes to techniques based on machine learning. The application of these techniques to accelerators is one of current hot topics in the field and pursued worldwide.
Uncertainties for large scale deep learning-based image reconstruction
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Starting date : 01-10-2021
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Personal web page : http://jstarck.cosmostat.org
Laboratory link : http://www.cosmostat.org
Deep learning (DL) has changed the way of solving inverse problems. Many scientific challenges remain that must be met for its deployment in astronomical imagery: i) taking into account the physical training model, ii) estimating the uncertainties on reconstructed images, iii) generalization, and iv ) the volume of data for scaling up. To quantify the uncertainties, we have introduced a probabilistic DL approach (Remy et al., 2020), which makes it possible to derive the a posteriori distribution of the solution. This requires however to use expensive simulation techniques (MCMC) which does not allow its use in ambitious projects like Euclid or SKA. Several challenges will be addressed in this thesis:
- Develop a new DL method to quantify uncertainties, while enjoying theoretical guarantees of coverage. We will rely on conformal quantile regression, a new method derived from theoretical statistics (Romano et al., 2019).
- Generalization: We recently proposed a new architecture of neural networks (the learnets, Ramsi et al., 2020), which has the advantage of including certain properties of the wavelet transform such as exact reconstruction. This type of architecture should provide a solution to the generalization problem.
- The scaling on data of dimension 3 or 4. It will then be a question of extending the results obtained in order to be able to efficiently handle this type of data.
The last challenge of this thesis will be to set up these new tools to solve problems in two large international projects, for dark matter maps with Euclid and SKA.
[1] B. Remy, F. Lanusse, Z. Ramzi, J. Liu, N. Jeffrey and J.-L. Starck, "Probabilistic Mapping of Dark Matter by Neural Score Matching", NeurIPS 2019 Machine Learning and the Physical Sciences Workshop.
[2] Y. Romano E. Patterson E. J. Candès, Conformalized quantile regression. Advances in neural information processing systems 32 NeurIPS, 2019.
[3] Z. Ramzi, JL Starck, T Moreau, P Ciuciu, "Wavelets in the deep learning era", European Signal Processing Conference, accepted submission to the EUSIPCO 2020 conference.
- Develop a new DL method to quantify uncertainties, while enjoying theoretical guarantees of coverage. We will rely on conformal quantile regression, a new method derived from theoretical statistics (Romano et al., 2019).
- Generalization: We recently proposed a new architecture of neural networks (the learnets, Ramsi et al., 2020), which has the advantage of including certain properties of the wavelet transform such as exact reconstruction. This type of architecture should provide a solution to the generalization problem.
- The scaling on data of dimension 3 or 4. It will then be a question of extending the results obtained in order to be able to efficiently handle this type of data.
The last challenge of this thesis will be to set up these new tools to solve problems in two large international projects, for dark matter maps with Euclid and SKA.
[1] B. Remy, F. Lanusse, Z. Ramzi, J. Liu, N. Jeffrey and J.-L. Starck, "Probabilistic Mapping of Dark Matter by Neural Score Matching", NeurIPS 2019 Machine Learning and the Physical Sciences Workshop.
[2] Y. Romano E. Patterson E. J. Candès, Conformalized quantile regression. Advances in neural information processing systems 32 NeurIPS, 2019.
[3] Z. Ramzi, JL Starck, T Moreau, P Ciuciu, "Wavelets in the deep learning era", European Signal Processing Conference, accepted submission to the EUSIPCO 2020 conference.
Machine learning for unmixing gravitational wave signals from the LISA interferometer
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Starting date : 01-09-2021
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Personal web page : www.jerome-bobin.fr
Following the first detections of gravitational waves in 2015, that were awarded the Nobel prize in Physics in 2017, a new window is now open to observe our Universe. In contrast to ground-based interferometers, the LISA observatory (Laser Interferometer Space Antenna) will be sensitive to a very large number of signals of different physical natures: galactic binaries, supermassive black holes, extreme mass ratio inspirals, etc. This wealth of signals raise paramount data analysis challenges: unmixing a large number of gravitational events of very different nature. The goal of this PhD thesis is to develop the first gravitational signal unmixing method for LISA. The proposed approach will make use of adapted signal representations for each category of signals to be retrieved, which will make profit of their different temporal signatures. The design of such representations will be based on advanced machine learning techniques. The proposed methods will be evaluated with the participation to the LISA Data Challenges (LDC).
Natural language processing in time domain astrophysics
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Starting date : 01-10-2021
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Personal web page : http://irfu.cea.fr/Pisp/fabian.schussler/index.html
Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3709
More : https://www.limsi.fr/fr/recherche/iles
Time domain and high-energy astrophysics is dealing with the most violent phenomena in the universe. Rapid exchange of information is crucial to detect these transient, i.e. short-lived, events with multiple observatories covering the full multi-wavelength domain and all cosmic messengers. Victim of its own success, the current way of manual reading, analyzing and classifying information shared by astrophysicists in Astronomers Telegrams or circulars within the Gamma-ray Coordinates Network is approaching saturation. One of the most promising novel approaches is to build on the recent progress in artificial intelligence and especially natural language processing (NLP) and feature extraction.
This thesis will bring together leading experts in two exiting domains: Artificial Intelligence and time domain, multi-messenger astrophysics. The project will be part of the UDOPIA program of the Paris-Saclay university and benefit from a rich ecosystem in both astrophysics and AI as well strong ties with leading industry partners.
This thesis will bring together leading experts in two exiting domains: Artificial Intelligence and time domain, multi-messenger astrophysics. The project will be part of the UDOPIA program of the Paris-Saclay university and benefit from a rich ecosystem in both astrophysics and AI as well strong ties with leading industry partners.
High-energy multi-messenger astrophysics with H.E.S.S. and CTA
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Starting date : 01-10-2021
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Personal web page : http://irfu.cea.fr/Pisp/fabian.schussler/index.html
Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3709
Very recently a fundamentally new domain of astronomy and astrophysics has shown its first results: multi-messenger and real-time astrophysics. The simultaneous detection of various new astrophysical messengers (gravitational waves, high-energy gamma rays and high-energy neutrinos) and the exchange and combination of data from very different observatories allows to open new windows and provides unprecedented insights into the most violent phenomena ever observed.
New and significant conclusions can be obtained by combining these new messengers. Joint analyses of archival observations in different wavelengths have brought enormous insights in the past and, as this technique provides an assured and certain scientific return, it will also be used in the proposed thesis project. At the same time it has becomes clear that another important step does greatly enhance the sensitivity of multi-messenger searches: the need to gain full access to the wealth of information provided by analyzing and combining the data in real-time. The proposed thesis project will allow opening this new window to the high-energy universe: real-time multi-messenger astronomy at very high energies. The combination of the various particles and radiations in a truly multi-messenger online alert system will resolve several challenges faced in high-energy astrophysics and especially allow detecting and studying violent transient phenomena that are supposed to be at the origin of high-energy cosmic rays. The project will introduce the time domain to high-energy astrophysics and has the potential to cause a paradigm shift in how observations and data analyses are performed.
The core of the proposed project will be H.E.S.S., currently the world’s most sensitive gamma-ray instrument, and CTA, the next generation, global high-energy gamma-ray observatory. We’ll combine their data with events recorded by IceCube, the world’s largest neutrino telescope and the advanced Virgo and Ligo gravitational wave interferometers. The detection of a transient high-energy gamma-ray source in coincidence with gravitational waves or high-energy neutrinos will provide the long sought evidence for their common origin and may resolve the century old quest for the origin of high-energy cosmic rays.
We’ll also collaborate with the world’s most sensitive radio observatories (e.g. the SKA precursors MeerKAT and ASKAP) to search for counterparts to Fast Radio Bursts and in general study a large variety of messengers like Gamma-Ray Bursts or flares from active galactic nuclei. By scanning the data acquired with high-energy gamma-ray observatories in real-time, it will also possible to send alerts to the wider astronomical community to ensure simultaneous observations at other wavelengths.
New and significant conclusions can be obtained by combining these new messengers. Joint analyses of archival observations in different wavelengths have brought enormous insights in the past and, as this technique provides an assured and certain scientific return, it will also be used in the proposed thesis project. At the same time it has becomes clear that another important step does greatly enhance the sensitivity of multi-messenger searches: the need to gain full access to the wealth of information provided by analyzing and combining the data in real-time. The proposed thesis project will allow opening this new window to the high-energy universe: real-time multi-messenger astronomy at very high energies. The combination of the various particles and radiations in a truly multi-messenger online alert system will resolve several challenges faced in high-energy astrophysics and especially allow detecting and studying violent transient phenomena that are supposed to be at the origin of high-energy cosmic rays. The project will introduce the time domain to high-energy astrophysics and has the potential to cause a paradigm shift in how observations and data analyses are performed.
The core of the proposed project will be H.E.S.S., currently the world’s most sensitive gamma-ray instrument, and CTA, the next generation, global high-energy gamma-ray observatory. We’ll combine their data with events recorded by IceCube, the world’s largest neutrino telescope and the advanced Virgo and Ligo gravitational wave interferometers. The detection of a transient high-energy gamma-ray source in coincidence with gravitational waves or high-energy neutrinos will provide the long sought evidence for their common origin and may resolve the century old quest for the origin of high-energy cosmic rays.
We’ll also collaborate with the world’s most sensitive radio observatories (e.g. the SKA precursors MeerKAT and ASKAP) to search for counterparts to Fast Radio Bursts and in general study a large variety of messengers like Gamma-Ray Bursts or flares from active galactic nuclei. By scanning the data acquired with high-energy gamma-ray observatories in real-time, it will also possible to send alerts to the wider astronomical community to ensure simultaneous observations at other wavelengths.
Multi-physics interaction between exoplanet atmospheres and their host stars
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/dap/LDEE/index.php (http://irfu.cea.fr/dap/LDEE/index.php)
The census of known exoplanets includes >4,000 planets in >3,000 systems. The current exoplanet demographics show that exoplanets exhibit a large diversity in their mass, radius (and thus density and composition) and orbital arrangements. The research field moves today from exoplanet detection to the characterization of their atmospheres. The focus of this project is to study numerically the physical mechanisms (3D dynamics, photochemistry, magnetic interactions) that drive the escape of strongly irradiated atmospheres. The project will provide insight into exoplanet systems for which upper atmospheric in-transit observations of e.g. Lyman-alpha, C II, H-alpha, He I at 1083 nm exist but that remain without a proper theoretical interpretation. Our priority is thus to develop physically-motivated models that embrace the complexity of these interactions and help place in context the available observables. We see this project as a first step into the development of a versatile and powerful 3D multi-physics model that can become the international reference for exoplanet-host star interactions.
Modelling magnetar formation
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Starting date : 01-10-2021
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Magnetars are neutron stars with the strongest magnetic fields known in the universe. The birth of these objects is one of the most studied scenarios to explain some of the most violent explosions: superluminous supernovae, hypernovae and gamma-ray bursts. Moreover, they emit at least some of the fast radio bursts, as demonstrated in 2020 by the detection of a radio burst from a galactic magnetar. The scientific exploitation of the increasingly abundant data from these various objects requires the development of more predictive models. One of the elements that is still incomplete concerns the prediction of magnetars magnetic field and their evolution. Recently, numerical simulations have succeeded in describing the formation of a magnetic field of comparable intensity to magnetars thanks to amplification mechanisms taking place in the first few seconds after the neutron star is formed. However, most of the observational manifestations of magnetars cited above require the magnetic field to survive on much longer time scales (from a few weeks for superluminous supernovae to thousands of years for soft gamma repeaters). This thesis aims to determine how the turbulent magnetic field generated in the first few seconds will evolve to a stable equilibrium state able to explain these observations.
ORIGIN AND DYNAMICS OF PROTOSTAR CLUSTERS
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Starting date : 01-10-2021
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Most stars are believed to form in groups or clusters (e.g. [6]), and our Sun itself may well have formed in a star cluster ([1]). Moreover, it appears that massive (> 10 Msun) stars may only form accompanied by a cluster of lower-mass stars. Our present theoretical understanding for the formation of protostars is, however, largely limited to single objects within isolated dense cloud cores (cf. [8]). Current theoretical models do not explain the statistical distribution of stellar masses (the so-called initial mass function - IMF - which seems quasi-universal) and neglect dynamical effects, such as interactions and collisions, which may play a crucial role in embedded young star clusters. To understand the origin of stellar masses and the physical conditions for the birth of the Solar system, it is of paramount importance to characterize the detailed properties of young (proto)star clusters, including their dynamics, in nearby molecular clouds. The latter provide ideal laboratories for star formation studies.
The results of extensive imaging surveys of nearby molecular clouds at submillimeter wavelengths with the Herschel space observatory suggest that the non-uniform spatial distribution or clustering of young stellar objects in star-forming regions is largely inherited from the filamentary structure of the parent clouds (cf. [2], [3], and Fig. 1). The Herschel observations do not provide direct constraints on the dynamics of nearby cluster-forming clouds, however. It is also unclear at which evolutionary stage protostars and young stellar objects decouple from the molecular gas of their parent cloud. These issues can now be addressed thanks to a combined analysis of the astrometric data (e.g. proper motions) from the Gaia satellite, the wide-field submillimeter images of the clouds from Herschel (e.g. Fig. 1), and additional millimeter line observations of the gas kinematics with the IRAM telescopes.
The thesis work will divided into four complementary tasks:
1) Systematic analysis of the protostellar content of the Herschel Gould Belt survey (HGBS) database ([3], http://gouldbelt- herschel.cea.fr/archives). The goal here will be to quantify the clustering of protostars in connection with the filamentary structure of the gas in nearby (d < 500 pc) molecular clouds, in a statistical manner. The Herschel data may be supplemented by higher-resolution observations at 350/450 microns with the ArTéMiS camera on APEX (cf. [5]).
2) Analysis of the Gaia DR2 database (e.g. [7]) to quantify the relative proper motions (in the plane of the sky) and internal dynamics of the young star population in the same clouds.
3) Complementary millimeter observational study of a portion of the same clouds in molecular lines with the IRAM telescopes to constrain the kinematics of the gas and assess the relative motions (projected on the line of sight) of protostars and protostellar dense cores (cf. [4]).
4) Comparison of the observational constraints coming from Herschel, Gaia, and IRAM data with numerical simulations of molecular cloud evolution performed with the adaptive mesh refinement code RAMSES available in the theoretical group of the AIM laboratory.
The results of extensive imaging surveys of nearby molecular clouds at submillimeter wavelengths with the Herschel space observatory suggest that the non-uniform spatial distribution or clustering of young stellar objects in star-forming regions is largely inherited from the filamentary structure of the parent clouds (cf. [2], [3], and Fig. 1). The Herschel observations do not provide direct constraints on the dynamics of nearby cluster-forming clouds, however. It is also unclear at which evolutionary stage protostars and young stellar objects decouple from the molecular gas of their parent cloud. These issues can now be addressed thanks to a combined analysis of the astrometric data (e.g. proper motions) from the Gaia satellite, the wide-field submillimeter images of the clouds from Herschel (e.g. Fig. 1), and additional millimeter line observations of the gas kinematics with the IRAM telescopes.
The thesis work will divided into four complementary tasks:
1) Systematic analysis of the protostellar content of the Herschel Gould Belt survey (HGBS) database ([3], http://gouldbelt- herschel.cea.fr/archives). The goal here will be to quantify the clustering of protostars in connection with the filamentary structure of the gas in nearby (d < 500 pc) molecular clouds, in a statistical manner. The Herschel data may be supplemented by higher-resolution observations at 350/450 microns with the ArTéMiS camera on APEX (cf. [5]).
2) Analysis of the Gaia DR2 database (e.g. [7]) to quantify the relative proper motions (in the plane of the sky) and internal dynamics of the young star population in the same clouds.
3) Complementary millimeter observational study of a portion of the same clouds in molecular lines with the IRAM telescopes to constrain the kinematics of the gas and assess the relative motions (projected on the line of sight) of protostars and protostellar dense cores (cf. [4]).
4) Comparison of the observational constraints coming from Herschel, Gaia, and IRAM data with numerical simulations of molecular cloud evolution performed with the adaptive mesh refinement code RAMSES available in the theoretical group of the AIM laboratory.
Measurement of the mass of galaxy clusters using gravitational lensing of the cosmic microwave background
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr
Galaxy clusters, located at the node of the cosmic web, are the largest gravitationally bound structures in the Universe. Their abundance and spatial distribution are very sensitive to cosmological parameters. Galaxy clusters thus constitute a powerful cosmological probe. They have proven to be an efficient probe in the last years (Planck, South Pole Telescope, XXL, etc.) and they are expected to make great progress in the coming years (Euclid, Vera Rubin Observatory, CMB-S4, etc.).
Theoretical predictions of the cluster abundance and spatial distribution depend on cosmological parameters and cluster mass. To determine cosmological parameters from cluster surveys, one needs to be able to measure accurately cluster mass. The error on the mass estimation is currently the main systematic error for the determination of cosmological parameters with galaxy clusters. This is the reason why it is crucial to improve on the measurement of the cluster mass and to control associated errors.
The most direct method to measure cluster mass is based on gravitational lensing. It is now used routinely in optical surveys: a cluster induces distortions of the shapes of background galaxies. Using these distortions, it is possible to reconstruct cluster mass. It was shown recently that it is also possible to detect these distortions at millimetre wavelengths in the cosmic microwave background (CMB) instead of using background galaxies, and reconstruct the mass of galaxy clusters. The main advantage of using the cosmic microwave background is because it is located at very high distance allowing for mass measurement of distant clusters; it is not possible to do this measurement with background galaxies, which are too few for distant clusters.
Irfu/DPhP has developed the first tools to measure galaxy cluster masses using gravitational lensing of the cosmic microwave background for the Planck mission. The PhD thesis work will consist in taking hands on the tools and improve them to make them compatible with ground-based data. They will then be applied to public SPT-SZ (https://pole.uchicago.edu) data and SPT-SZ+Planck data jointly. The ACT (https://act.princeton.edu) data has also been made public recently and a joint analysis ACT+Planck will also be made.
In the second part of the thesis, the tools will be used to find observation strategies and compute integration times to measure cluster masses for high resolution ground based experiments such as NIKA2 (http://ipag.osug.fr/nika2/), alone and jointly with Planck.
The current methods are optimal for maps in total intensity and in the low signal-to-noise regime as shown in the Figure above. The future experiments will have lower noise levels and will be very sensitive to polarization. The third part of the thesis will be dedicated to development of new methods to extract the masses for the future low noise cosmic microwave background experiments such as CMB-S4 (https://cmb-s4.org), PICO (arXiv:1902.10541) or CMB Backlight (arXiv: 1909.01592).
Finally, we will study the precision on cosmological parameters that can be reached from galaxy cluster catalogues, given the precision on the mass expected from these future experiments.
Theoretical predictions of the cluster abundance and spatial distribution depend on cosmological parameters and cluster mass. To determine cosmological parameters from cluster surveys, one needs to be able to measure accurately cluster mass. The error on the mass estimation is currently the main systematic error for the determination of cosmological parameters with galaxy clusters. This is the reason why it is crucial to improve on the measurement of the cluster mass and to control associated errors.
The most direct method to measure cluster mass is based on gravitational lensing. It is now used routinely in optical surveys: a cluster induces distortions of the shapes of background galaxies. Using these distortions, it is possible to reconstruct cluster mass. It was shown recently that it is also possible to detect these distortions at millimetre wavelengths in the cosmic microwave background (CMB) instead of using background galaxies, and reconstruct the mass of galaxy clusters. The main advantage of using the cosmic microwave background is because it is located at very high distance allowing for mass measurement of distant clusters; it is not possible to do this measurement with background galaxies, which are too few for distant clusters.
Irfu/DPhP has developed the first tools to measure galaxy cluster masses using gravitational lensing of the cosmic microwave background for the Planck mission. The PhD thesis work will consist in taking hands on the tools and improve them to make them compatible with ground-based data. They will then be applied to public SPT-SZ (https://pole.uchicago.edu) data and SPT-SZ+Planck data jointly. The ACT (https://act.princeton.edu) data has also been made public recently and a joint analysis ACT+Planck will also be made.
In the second part of the thesis, the tools will be used to find observation strategies and compute integration times to measure cluster masses for high resolution ground based experiments such as NIKA2 (http://ipag.osug.fr/nika2/), alone and jointly with Planck.
The current methods are optimal for maps in total intensity and in the low signal-to-noise regime as shown in the Figure above. The future experiments will have lower noise levels and will be very sensitive to polarization. The third part of the thesis will be dedicated to development of new methods to extract the masses for the future low noise cosmic microwave background experiments such as CMB-S4 (https://cmb-s4.org), PICO (arXiv:1902.10541) or CMB Backlight (arXiv: 1909.01592).
Finally, we will study the precision on cosmological parameters that can be reached from galaxy cluster catalogues, given the precision on the mass expected from these future experiments.
THE ROLE OF MAGNETIC FIELDS IN STAR-FORMING FILAMENTS: USING THE LARGE OBSERVING PROGRAM 'B-FUN' WITH NIKA2-POL TO PAVE THE WAY FOR THE B-BOP POLARIMETER IN SPACE
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/dap/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3627
More : https://ipag.osug.fr/nika2//Welcome.html
Imaging surveys of nearby molecular clouds at submillimeter wavelengths with the Herschel and Planck satellites have revolutionized our understanding of the link between the structure of the interstellar medium (ISM) and the early phases of the star formation process. The results of these surveys support a paradigm of star formation in which magnetized filaments play a central role. In particular, Herschel results indicate that most (> 75%) cores/stars form in dense, « supercritical » filaments of ~ 0.1 pc width for which the mass per unit length exceeds the critical line mass of nearly isothermal gas cylinders, and Planck polarization data suggest that the formation and evolution of these filaments is largely controlled by magnetic fields.
The low resolution of Planck polarization observations (5’-10’ at best or 0.2-0.4 pc in the nearest star-forming regions) was however insufficient to probe individual cores along filaments and to understand the role of magnetic fields in filament evolution and fragmentation. This is now becoming possible with new imaging polarimeters such as SOFIA-HAWC+ (18'' resolution at 214 microns) and NIKA2-Pol (12’’ resolution at 1.2mm), the polarimeter that will very soon be available on the new millimeter continuum camera NIKA2 of the IRAM 30m telescope (cf. http://www.iram-institute.org/EN/news-astronomers/2016/118.html and http://ipag.osug.fr/nika2/Welcome.html).
A total of 300 hr of NIKA2 guaranteed time have been set aside for a large polarimetric imaging survey of ~ 10 nearby star-forming filaments with NIKA2-Pol (PI : Ph. André).
The goal of the proposed PhD thesis will be to participate in these polarimetric observations and to interpret the polarization results, based on a detailed comparison with numerical simulations of magnetized cloud collapse and fragmentation obtained with the AMR code RAMSES available in the AIM Theory group.
The low resolution of Planck polarization observations (5’-10’ at best or 0.2-0.4 pc in the nearest star-forming regions) was however insufficient to probe individual cores along filaments and to understand the role of magnetic fields in filament evolution and fragmentation. This is now becoming possible with new imaging polarimeters such as SOFIA-HAWC+ (18'' resolution at 214 microns) and NIKA2-Pol (12’’ resolution at 1.2mm), the polarimeter that will very soon be available on the new millimeter continuum camera NIKA2 of the IRAM 30m telescope (cf. http://www.iram-institute.org/EN/news-astronomers/2016/118.html and http://ipag.osug.fr/nika2/Welcome.html).
A total of 300 hr of NIKA2 guaranteed time have been set aside for a large polarimetric imaging survey of ~ 10 nearby star-forming filaments with NIKA2-Pol (PI : Ph. André).
The goal of the proposed PhD thesis will be to participate in these polarimetric observations and to interpret the polarization results, based on a detailed comparison with numerical simulations of magnetized cloud collapse and fragmentation obtained with the AMR code RAMSES available in the AIM Theory group.
Measuring the growth of massive structures in the distant Universe with deep spectroscopic surveys
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Starting date : 01-10-2021
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Dark Energy Tomography with the Euclid survey
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Starting date : 01-10-2021
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Personal web page : https://www.valeriapettorino.com/
Laboratory link : http://www.cosmostat.org/
While the Universe is expanding with increasing velocity, the question of what is causing cosmic acceleration remains unsolved. Acceleration seems to act against gravitational attraction, as if a new source of energy, dubbed dark energy, were responsible for it.
This PhD proposal is meant to contribute to the Euclid mission, to tackle this dilemma by implementing the possibility to test dark energy at different redshifts, or what I refer to here as ‘dark energy tomography’, and integrate it in the Euclid Consortium validated likelihood.
The PhD student will be able to work at the interface between data and theory and concretely collaborate to a large collaboration like the Euclid satellite. Objectives include 1) extending the likelihood software to test dark energy at different redshift epochs, 2) contribute to the collaboration effort on comparing theoretical predictions with data 3) investigate different machine learning methods to reconstruct the dark energy contribution in each redshift bin.
This PhD proposal is meant to contribute to the Euclid mission, to tackle this dilemma by implementing the possibility to test dark energy at different redshifts, or what I refer to here as ‘dark energy tomography’, and integrate it in the Euclid Consortium validated likelihood.
The PhD student will be able to work at the interface between data and theory and concretely collaborate to a large collaboration like the Euclid satellite. Objectives include 1) extending the likelihood software to test dark energy at different redshift epochs, 2) contribute to the collaboration effort on comparing theoretical predictions with data 3) investigate different machine learning methods to reconstruct the dark energy contribution in each redshift bin.
Impact of the density of galaxies in the analysis of the large spectroscopic survey DESI
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Starting date : 01-10-2021
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In the last 30 years, the study of the Universe has seen the emergence of a standard model of the Universe based on general relativity. In this model, our Universe is made of ordinary matter, dark matter and a mysterious component called “dark energy”, responsible for the recent acceleration of the expansion of the universe. The upcoming large surveys, such as DESI in the US, will provide a map of the distribution of the galaxies 10 times more precise than the current state-of-the-art. The scientific community is gearing up to define new analysis techniques in order to extract the maximum of information from these surveys and hence enter the era of precision cosmology especially as far as growth of structure measurements are concerned. In this thesis, we propose to study a novel approach based on using the density at large scales to improve the precision on those measurements and to compare it with General Relativity predictions in order to search for possible deviations.
The thesis will take place at Irfu, the Institute for Research on the Fundamental laws of the Universe. The PhD student will join the cosmology group of Irfu/DPhP, composed of 10 physicists, 4 PhD students and 2 post-docs. Actively involved in the eBOSS and DESI experiments, the group also participates in Euclid and has in the past had a strong contribution in the SNLS, Planck and BOSS international collaborations. The future PhD student will be integrated into the DESI collaboration and will benefit from all the group’s expertise acquired on BOSS and eBOSS
The thesis will take place at Irfu, the Institute for Research on the Fundamental laws of the Universe. The PhD student will join the cosmology group of Irfu/DPhP, composed of 10 physicists, 4 PhD students and 2 post-docs. Actively involved in the eBOSS and DESI experiments, the group also participates in Euclid and has in the past had a strong contribution in the SNLS, Planck and BOSS international collaborations. The future PhD student will be integrated into the DESI collaboration and will benefit from all the group’s expertise acquired on BOSS and eBOSS
Towards a 3D characterisation of supernova remants in X-rays
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Starting date : 01-10-2021
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More : http://github.com/facero/sujets2021
X-ray data are multidimensional by nature. For each photon the energy and position is recorded by the X-ray satellite. Here we propose to develop novel techniques to fully exploit the multidimensional nature of the data by combining blind source separation technique with feature learning.
Characterization of SVOM Gamma-Ray Bursts Afterglows using MXT data
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Starting date : 01-10-2021
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More : http://www.svom.fr
SVOM is a mission dedicated to the detection and characterization of Gamma-Ray Bursts (GRBs) and other multi-messenger sources, and it is scheduled for launch in June 2022.
SVOM carries a unique multi-wavelength payload, sensitive from gamma-rays to the visible band, which is complemented on ground by dedicated wide field and narrow field robotic telescopes, distributed over the entire Earth. The SVOM space segment consists of ECLAIRS, a coded mask telescope operating in the 4-150 keV energy range, GRM, a gamma-ray (20 keV-5 MeV) spectrometer, and two follow-up narrow field telescopes, VT (visible) and MXT (0.2-10 keV). The Microchannel X-ray Telescope (MXT) is a compact and light focusing X-ray telescope. The main goal of MXT is to precisely localize the X-ray counterparts of SVOM GRBs and to study in detail their spectral and temporal characteristics.
Gamma-Ray Bursts are issued either by the collapse of a very massive star (> 50 times the mass of the Sun) or by the coalescence of two compact objects (most likely neutron stars). In both scenari a short lived (less than ~100 s) gamma ray emission is followed by a longer lived (hours to days) X-ray emission, that can provide useful information about the GRB environment, the associated emission processes and, possibly, the nature of the GRB progenitors.
The successful PHD candidate will in first place contribute to the analysis the MXT flight model calibration data obtained in summer 2021 at the PANTER X-ray testing facility. In particular, the PHD student will be in charge of producing the MXT spectral response matrices before the SVOM launch, and of updating them during the first two years of the mission, by analyzing the in-flight calibration data.
The PHD student will be part of the MXT science team, act as a SVOM Burst Advocate, and thanks to this experience and to the deep instrumental knowledge acquired she/he will be able to correctly analyze, since the very beginning of the SVOM mission, X-ray afterglow data, and couple them to the multi wavelength data in order to build a clear phenomenological picture of the SVOM GRBs. In fact, the early GRB afterglow phase is still not fully understood, in particular from the point of view of the contribution of the GRB central engine to the so-called “plateau phases” of the afterglow light curve, whose interpretation could lead to a better understanding of the GRB progenitors.
SVOM carries a unique multi-wavelength payload, sensitive from gamma-rays to the visible band, which is complemented on ground by dedicated wide field and narrow field robotic telescopes, distributed over the entire Earth. The SVOM space segment consists of ECLAIRS, a coded mask telescope operating in the 4-150 keV energy range, GRM, a gamma-ray (20 keV-5 MeV) spectrometer, and two follow-up narrow field telescopes, VT (visible) and MXT (0.2-10 keV). The Microchannel X-ray Telescope (MXT) is a compact and light focusing X-ray telescope. The main goal of MXT is to precisely localize the X-ray counterparts of SVOM GRBs and to study in detail their spectral and temporal characteristics.
Gamma-Ray Bursts are issued either by the collapse of a very massive star (> 50 times the mass of the Sun) or by the coalescence of two compact objects (most likely neutron stars). In both scenari a short lived (less than ~100 s) gamma ray emission is followed by a longer lived (hours to days) X-ray emission, that can provide useful information about the GRB environment, the associated emission processes and, possibly, the nature of the GRB progenitors.
The successful PHD candidate will in first place contribute to the analysis the MXT flight model calibration data obtained in summer 2021 at the PANTER X-ray testing facility. In particular, the PHD student will be in charge of producing the MXT spectral response matrices before the SVOM launch, and of updating them during the first two years of the mission, by analyzing the in-flight calibration data.
The PHD student will be part of the MXT science team, act as a SVOM Burst Advocate, and thanks to this experience and to the deep instrumental knowledge acquired she/he will be able to correctly analyze, since the very beginning of the SVOM mission, X-ray afterglow data, and couple them to the multi wavelength data in order to build a clear phenomenological picture of the SVOM GRBs. In fact, the early GRB afterglow phase is still not fully understood, in particular from the point of view of the contribution of the GRB central engine to the so-called “plateau phases” of the afterglow light curve, whose interpretation could lead to a better understanding of the GRB progenitors.
Study of Polarimetric Bolometer Arrays with Spectroscopic Capabilities for Astrophysics
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/dap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=2755
The Herschel Space Observatory, launched in 2009, has revolutionized our vision of the "Cold Universe". In particular, it has radically changed our understanding of star formation by highlighting the ubiquitous filamentary structures of gas and dust and their essential role in the very early stages of star formation.
On the other hand, the observations of the Planck satellite (also launched in 2009) in polarimetric mode have highlighted the presence of magnetic fields on large scales in molecular clouds. In these regions, the filaments can be either parallel to the magnetic field (low density filaments) or perpendicular (very dense filaments). But many questions remain.
In order to understand the set of physical processes implemented in these stellar formation zones and to explain the links with the complex structure of the surrounding interstellar medium (ISM), new extremely sensitive instruments must be developed in the submillimeter domain. It seems necessary, on the one hand, to be able to finely characterize the magnetic field (via the detection of polarized light) in several spectral bands and, on the other hand, to detect the presence of several tracers of the ISM via the emission of certain spectral lines (C+ at 158 µm in particular). These observations, made from space or aboard stratospheric balloons, strongly constrain the volume and mass of the on-board charge. The idea of gathering one or more light analysis functions within a compact detector is a step in this direction.
In this context, CEA has been developing for a few years now ultra-sensitive submillimeter bolometer arrays, capable of measuring the polarization within pixels, without the help of external polarizers. Developed in close collaboration with CEA-LETI in the framework of the B-BOP instrument on the SPICA observatory, this technology is in line with the developments of the Herschel-PACS detectors. These bolometers are developed in the framework of Labex Focus, 2 R&T CNES and ESA funding.
In 2019, a thesis defended at the laboratory demonstrated that it was possible to add spectroscopic capacity to these new generation arrays by coupling the detector arrays to a compact Fabry-Perot interferometric system. The experimental demonstration of the complete device remains to be done and this is the core of this thesis topic: to study, implement and characterize experimentally the scientific performances of this compact spectro-imager-polarimeter.
The first step will be to experimentally validate in a cryostat the Fabry-Perot mirror displacement system and to deduce its technical limitations. The second phase will consist in coupling this system to the bolometer arrays in order to produce and characterize the first prototypes of this new type of detectors. Finally, in a third part, the data processing aspect will be studied in order to extract the scientific signal as well as possible and to propose an adequate calibration.
This work may also pave the way to more applied applications in medical imaging or in the field of security controls in the TeraHertz band, as proposed by LETI with its developments of room temperature micro-bolometers.
On the other hand, the observations of the Planck satellite (also launched in 2009) in polarimetric mode have highlighted the presence of magnetic fields on large scales in molecular clouds. In these regions, the filaments can be either parallel to the magnetic field (low density filaments) or perpendicular (very dense filaments). But many questions remain.
In order to understand the set of physical processes implemented in these stellar formation zones and to explain the links with the complex structure of the surrounding interstellar medium (ISM), new extremely sensitive instruments must be developed in the submillimeter domain. It seems necessary, on the one hand, to be able to finely characterize the magnetic field (via the detection of polarized light) in several spectral bands and, on the other hand, to detect the presence of several tracers of the ISM via the emission of certain spectral lines (C+ at 158 µm in particular). These observations, made from space or aboard stratospheric balloons, strongly constrain the volume and mass of the on-board charge. The idea of gathering one or more light analysis functions within a compact detector is a step in this direction.
In this context, CEA has been developing for a few years now ultra-sensitive submillimeter bolometer arrays, capable of measuring the polarization within pixels, without the help of external polarizers. Developed in close collaboration with CEA-LETI in the framework of the B-BOP instrument on the SPICA observatory, this technology is in line with the developments of the Herschel-PACS detectors. These bolometers are developed in the framework of Labex Focus, 2 R&T CNES and ESA funding.
In 2019, a thesis defended at the laboratory demonstrated that it was possible to add spectroscopic capacity to these new generation arrays by coupling the detector arrays to a compact Fabry-Perot interferometric system. The experimental demonstration of the complete device remains to be done and this is the core of this thesis topic: to study, implement and characterize experimentally the scientific performances of this compact spectro-imager-polarimeter.
The first step will be to experimentally validate in a cryostat the Fabry-Perot mirror displacement system and to deduce its technical limitations. The second phase will consist in coupling this system to the bolometer arrays in order to produce and characterize the first prototypes of this new type of detectors. Finally, in a third part, the data processing aspect will be studied in order to extract the scientific signal as well as possible and to propose an adequate calibration.
This work may also pave the way to more applied applications in medical imaging or in the field of security controls in the TeraHertz band, as proposed by LETI with its developments of room temperature micro-bolometers.
Intergalactic magnetic field and gamma ray bursts with CTA
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Starting date : 01-09-2021
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Personal web page : http://irfu.cea.fr/Pisp/thierry.stolarczyk/
Laboratory link : http://irfu.cea.fr/en/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3709
More : http://www.cta-observatory.org/
The intergalactic magnetic field pervading the cosmic voids is suspected to be a relic field originating from the very first epoch of the cosmic history. The goal of this PhD is to look for signatures of this field in the high-energy data of gamma-ray bursts, and to predict the ability of the future CTA observatory to constrain its properties. This work combines both theoretical modelling and analysis of simulated CTA data.
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Starting date : 01-10-2021
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Personal web page : http://irfu.cea.fr/Pisp/matthias.gonzalez/
Laboratory link : http://irfu.cea.fr/Sap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=1250
Cosmology - Clusters of galaxies - Artificial intelligence
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Starting date : 01-10-2021
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Personal web page : https://sci.esa.int/s/WLg9apw
Laboratory link : http://irfu.cea.fr/dap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=972
More : Projet XXL : http://irfu.cea.fr/xxl
Clusters of galaxies are the most massive entities in the universe. As such, they constitute powerful cosmological probes.
The XLL survey is the largest programme of the European satellite XMM (X-ray band). It has enabled the detection of several hundreds of galaxy clusters.
The goal of the PhD is to perform the cosmological analysis of the complete XXL cluster sample by using innovative machine learning techniques.
The XLL survey is the largest programme of the European satellite XMM (X-ray band). It has enabled the detection of several hundreds of galaxy clusters.
The goal of the PhD is to perform the cosmological analysis of the complete XXL cluster sample by using innovative machine learning techniques.
Inventive Conditions and Dimensions of Digital Design
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Starting date : 01-05-2021
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Laboratory link : http://iramis.cea.fr/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=748
More : https://www.octo.com/
A large part of digital innovation is structured by a few technological clusters anchored in specific geographic sites (Silicon Valley, Shenzhen, etc.). These places are ecosystems, that is to say natural, social and technical environments, which play the role of "technological terroirs".
The first objective of this thesis is to clarify the specificity and impact of these original local contexts regarding inventiveness in digital design. On the one hand, they welcome and generate the possibility of innovation; on the other hand, they modulate and organize a global space, made up of all the territories connected to information networks. The Paris-Saclay Campus will be one of the study sites. The activities of OCTO Technology will provide others.
The notion of design designates a recursive design process that produces and evolves a technical object by integrating the constraints and resources resulting from its social and cultural integration. The philosopher of technology Gilbert Simondon has developed a method to analyze the invention and evolution of technical lineages in relation to their "associated milieu". This thesis will measure the relevance of these concepts applied to digital objects, revise them and supplement them with the contribution of other thinkers of digital technologies.
The deployment of algorithms or artificial intelligences is the result of a complex process of dissemination operating at multiple scales. An analysis of the conditions for inventiveness in terms of design regimes and middle grounds is relevant. However, the property of "scalability" is specific to digital design (due to marginal cost replication) and transforms the dimensions of this process. The thesis will therefore have to take into account the scale relativity in order to objectify the different levels where the inventiveness of digital design operates.
This thesis requires a reflection that embraces the richness and diversity of technological dimensions, including its ethical dimension. It should lead to avenues, for the CEA as well as for OCTO technology, aimed at promoting the emergence of digital innovations from the eco-responsible perspective of "right technology".
The first objective of this thesis is to clarify the specificity and impact of these original local contexts regarding inventiveness in digital design. On the one hand, they welcome and generate the possibility of innovation; on the other hand, they modulate and organize a global space, made up of all the territories connected to information networks. The Paris-Saclay Campus will be one of the study sites. The activities of OCTO Technology will provide others.
The notion of design designates a recursive design process that produces and evolves a technical object by integrating the constraints and resources resulting from its social and cultural integration. The philosopher of technology Gilbert Simondon has developed a method to analyze the invention and evolution of technical lineages in relation to their "associated milieu". This thesis will measure the relevance of these concepts applied to digital objects, revise them and supplement them with the contribution of other thinkers of digital technologies.
The deployment of algorithms or artificial intelligences is the result of a complex process of dissemination operating at multiple scales. An analysis of the conditions for inventiveness in terms of design regimes and middle grounds is relevant. However, the property of "scalability" is specific to digital design (due to marginal cost replication) and transforms the dimensions of this process. The thesis will therefore have to take into account the scale relativity in order to objectify the different levels where the inventiveness of digital design operates.
This thesis requires a reflection that embraces the richness and diversity of technological dimensions, including its ethical dimension. It should lead to avenues, for the CEA as well as for OCTO technology, aimed at promoting the emergence of digital innovations from the eco-responsible perspective of "right technology".
Design of a novel Analog to Digital Converter with internal Machine Learning calibration
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/dedip/index.php
In current and future high energy physics experiments (as the LHC at CERN), the particle detector uses sub-micron integrated circuits. The signals from these circuits are digitized upstream of the processing chain and conveyed far from the experience by ultra-fast digital links. The development of new analog to digital converters (ADC) that perform well in potentially extreme environments, especially in radiation environments, is a challenge. Up to now, the trend has been to make these circuit responses stable and insensitive to variations in T°, dose or technology. Another possibility is to establish precise calibration tables that can be "downloaded" into the ASIC when conditions change or, even better, automatically generated by the ASIC itself.
This calibration parameter generation, in or outside of the ASIC, can be considered in the Machine Learning (ML) context.
The thesis approach is therefore to understand both the complexity of a real ADC and the software analysis of the errors correction, by carrying out the ML algorithms resulting in the ADC calibration. With an accurate ADC calibration, it is also foreseen to greatly enhanced the ADC performance by combining several ADC channels into one, leading to conversion rates or resolutions unreachable for a single core ADC.
This calibration parameter generation, in or outside of the ASIC, can be considered in the Machine Learning (ML) context.
The thesis approach is therefore to understand both the complexity of a real ADC and the software analysis of the errors correction, by carrying out the ML algorithms resulting in the ADC calibration. With an accurate ADC calibration, it is also foreseen to greatly enhanced the ADC performance by combining several ADC channels into one, leading to conversion rates or resolutions unreachable for a single core ADC.
Design of a new readout circuit for highly pixelated hybrid detectors for hard X-ray spectro-imaging and polarimetry space applications.
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Starting date : 01-10-2021
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This space instrumentation thesis consists in designing a microelectronic matrix circuit integrating numerous analog and digital functions in 250 µm pixels for the reading of CdTe or silicon semiconductor detectors.
Since 2011, our research team has been developing a new concept of hybrid detectors called MC2 (Mini CdTe on Chip) based on 3D WDoD(TM) (wireless die on die) technologies that should support the thermomechanical and radiative environment of a space mission. The ambition is to realize large focal planes with unequalled performances in time-resolved spectro-imaging and polarimetry, intended to serve the next discoveries in X and gamma astrophysics and solar flare physics.
The targeted microelectronics technology is the XFAB 180 nm technology, which is particularly attractive for space applications due to its perennial and affordable commercial availability and its good radiation resistance. It is a credible choice as an alternative to the AMS 0.35 µm technology, massively exploited until now, especially for the space projects SVOM (gamma camera ECLAIRs) and Solar Orbiter (X STIX telescope) in our group. Future generations of our detectors will be able to benefit from this advantageous technology in R&D as well as in production, even in cases where the dose resistance is important.
Two generations of matrix circuits realized in the XFAB 180 nm technology have shown very promising results to integrate ultra low noise and low power self-triggered spectroscopy chains in a 250 µm pixel side. These circuits have also shown the need to design, characterize and optimize several critical functions at the pixel level, common blocks and inter-pixel operators in order to obtain a better response uniformity and the desired ultimate noise level. The objective of the thesis is to provide innovative and high-performance solutions for a new circuit of 32 x 32 pixels with a 250 µm pitch, connectable on 2 sides, with an optimized interface and a modular architecture to be integrated in a spatially-integrated detection module.
Spinoffs from these developments are also envisaged in the medical field, notably for breast cancer tomography, as well as in the field of environmental monitoring in the nuclear field.
Since 2011, our research team has been developing a new concept of hybrid detectors called MC2 (Mini CdTe on Chip) based on 3D WDoD(TM) (wireless die on die) technologies that should support the thermomechanical and radiative environment of a space mission. The ambition is to realize large focal planes with unequalled performances in time-resolved spectro-imaging and polarimetry, intended to serve the next discoveries in X and gamma astrophysics and solar flare physics.
The targeted microelectronics technology is the XFAB 180 nm technology, which is particularly attractive for space applications due to its perennial and affordable commercial availability and its good radiation resistance. It is a credible choice as an alternative to the AMS 0.35 µm technology, massively exploited until now, especially for the space projects SVOM (gamma camera ECLAIRs) and Solar Orbiter (X STIX telescope) in our group. Future generations of our detectors will be able to benefit from this advantageous technology in R&D as well as in production, even in cases where the dose resistance is important.
Two generations of matrix circuits realized in the XFAB 180 nm technology have shown very promising results to integrate ultra low noise and low power self-triggered spectroscopy chains in a 250 µm pixel side. These circuits have also shown the need to design, characterize and optimize several critical functions at the pixel level, common blocks and inter-pixel operators in order to obtain a better response uniformity and the desired ultimate noise level. The objective of the thesis is to provide innovative and high-performance solutions for a new circuit of 32 x 32 pixels with a 250 µm pitch, connectable on 2 sides, with an optimized interface and a modular architecture to be integrated in a spatially-integrated detection module.
Spinoffs from these developments are also envisaged in the medical field, notably for breast cancer tomography, as well as in the field of environmental monitoring in the nuclear field.
Deep Learning and gamma spectroscopy: a new signal processing approach for CdTe detectors data analysis
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Starting date : 01-10-2021
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This thesis at the interface between nuclear instrumentation and applied mathematics consists in developing and implementing advanced methods for processing spectral data from CdTe Caliste detectors for high-energy photons. These sensors, resulting from fundamental research in space astrophysics, are the basic building block of the Spid-X gamma camera born from joint technological developments between the CEA and the company 3D PLUS. It aims at characterizing radiative environments in the framework of nuclear surveillance, for the safety of nuclear operations or research facilities, or for the dismantling of installations.
The methods studied will use Deep Learning tools with the objective of analyzing gamma spectra acquired in a complex environment inducing spectral distortions, potentially difficult to interpret with classical algorithms.
For this purpose, the PhD student will carry out the following lines of study:
- The identification of radioelements and the measurement of their proportion in the signal with one or several absorbing and scattering materials between the sources and the detector (methods: Monte-Carlo Geant4 simulations, Bayesian neural networks, confidence robust learning and experimentation).
- Determination of the nature of the material crossed and the thickness crossed (methods: adversarial neural networks (GANs), self-encoding, experimentation).
- The application to coded mask imaging methods. Depending on the results obtained in the two previous axes and the resulting discovery space, the methods may be applied to the theme of coded mask methods for gamma-ray imaging.
The methods studied will use Deep Learning tools with the objective of analyzing gamma spectra acquired in a complex environment inducing spectral distortions, potentially difficult to interpret with classical algorithms.
For this purpose, the PhD student will carry out the following lines of study:
- The identification of radioelements and the measurement of their proportion in the signal with one or several absorbing and scattering materials between the sources and the detector (methods: Monte-Carlo Geant4 simulations, Bayesian neural networks, confidence robust learning and experimentation).
- Determination of the nature of the material crossed and the thickness crossed (methods: adversarial neural networks (GANs), self-encoding, experimentation).
- The application to coded mask imaging methods. Depending on the results obtained in the two previous axes and the resulting discovery space, the methods may be applied to the theme of coded mask methods for gamma-ray imaging.
Moderne imagery techniques for neutronography
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Starting date : 01-10-2021
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Neutronography, or neutron radiography, consists of producing a 2D image of an object crossed by a neutron flux by measuring the differences in absorption and scattering of these particles as they pass through the materials. It is a non-destructive diagnostic and these images have extremely interesting characteristics, very different from those obtained by X-ray. Indeed, neutrons, which are essentially sensitive to the nuclear interaction, are affected by light chemical elements (hydrogen), present in particular in organic materials, whereas most heavier elements, such as metals, are transparent to them. Neutronography thus finds unique applications in materials science, engineering, archaeology or the study of works of art.
Until now, nuclear research reactors have been producing neutrons, but these facilities are at the end of their lives, such as the Orphée reactor in Saclay, which was shut down in 2019. Alternative sources are developed, based on neutrons emitted during nuclear reactions produced by a beam of accelerated particles (e.g. protons), such as the SONATE project. These new facilities are cheaper and more flexible than nuclear reactors, but provide lower neutron fluxes. To avoid excessively long measurement times, it is necessary to use imaging technologies that are more sensitive than traditional silver films. The aim of this thesis is to qualify different modern imaging technologies and to optimise them for industrial neutronography. Different detector technologies are possible: detectors based on microchannel wafers, or detectors based on scintillating films coupled with CCD cameras. The analysis of the signals from these detectors can also be optimised, and the "event by event" mode can be studied to improve the selectivity and resolution of the images. Finally, post-processing of the image, based on noise reduction and super-resolution algorithms, can also be used, which can make use of advanced machine learning methods for image reconstruction, potentially allowing a gain in reconstruction quality as well as rapid analysis.
Until now, nuclear research reactors have been producing neutrons, but these facilities are at the end of their lives, such as the Orphée reactor in Saclay, which was shut down in 2019. Alternative sources are developed, based on neutrons emitted during nuclear reactions produced by a beam of accelerated particles (e.g. protons), such as the SONATE project. These new facilities are cheaper and more flexible than nuclear reactors, but provide lower neutron fluxes. To avoid excessively long measurement times, it is necessary to use imaging technologies that are more sensitive than traditional silver films. The aim of this thesis is to qualify different modern imaging technologies and to optimise them for industrial neutronography. Different detector technologies are possible: detectors based on microchannel wafers, or detectors based on scintillating films coupled with CCD cameras. The analysis of the signals from these detectors can also be optimised, and the "event by event" mode can be studied to improve the selectivity and resolution of the images. Finally, post-processing of the image, based on noise reduction and super-resolution algorithms, can also be used, which can make use of advanced machine learning methods for image reconstruction, potentially allowing a gain in reconstruction quality as well as rapid analysis.
Neutron and beta imaging with Micromegas detectors with optical readout
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Starting date : 01-10-2021
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Personal web page : http://irfu.cea.fr/Pisp/esther.ferrer-ribas/
Laboratory link : http://irfu.cea.fr/dedip/index.php
Recent developments have shown that coupling a Micromegas gaseous detector on a glass substrate with a transparent anode and a CCD camera enable the optical readout of Micromegas detectors with an impressive spatial resolution showing that the glass Micromegas detector is well-suited for imaging. This feasibility test has been effectuated with low-X-ray photons permitting energy resolved imaging. This test opens the way to different applications. Here we will focus, on one hand, on neutron imaging for non-destructive examination of highly gamma-ray emitting objects, such as fresh irradiated nuclear fuel or radioactive waste and on the other hand, we would like to develop a beta imager at the cell level in the field of anticancerous drug studies.
Both applications require gas simulations to optimize light yields, optimization of the camera operation mode and design of the detectors in view of the specific constraints of reactor dismantling and medical applications: spatial resolution and strong gamma suppression for neutron imaging and precise rate and energy spectrum measurements for the beta. The image acquisition will be optimized for each case and dedicated processing algorithms will be developed.
Both applications require gas simulations to optimize light yields, optimization of the camera operation mode and design of the detectors in view of the specific constraints of reactor dismantling and medical applications: spatial resolution and strong gamma suppression for neutron imaging and precise rate and energy spectrum measurements for the beta. The image acquisition will be optimized for each case and dedicated processing algorithms will be developed.
Pushing ab initio calculations of atomic nuclei to higher precision
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=4070
Pushing ab initio calculations of atomic nuclei to higher precision
The theoretical description of atomic nuclei from first principles, or in a so-called ab initio fashion, has become possible only recently thanks to crucial advances in many-body theory and the availability of increasingly powerful high-performance computers. Such ab initio techniques are being successfully applied to study the structure of nuclei starting from the lighter isotopes. Still, extensions to heavy elements and nuclear reactions are posing considerable difficulties. The objective of the thesis is to contribute to this on-going progress in nuclear many-body theory. The project will focus on a developing ab initio technique (the so-called Gorkov-Green function approach, devised at CEA Saclay) designed to describe open-shell or superfluid systems (the majority of atomic nuclei). After the first promising applications to light and medium-mass nuclei, the method faces crucial upgrades to reach the precision and competitiveness of state-of-the-art approaches. The proposed work will aim to put in place the necessary tools towards this direction.
In particular, the Gorkov-Green function approach will be extended to the next level of precision. After some formal work, this will require a careful numerical implementation on top of the existing code. Given the increased cost of the corresponding numerical calculations, expected to go from moderately (100 proc.) to massively parallel (1000 proc.), special attention will have to be paid to the code optimisation and the use of pre-processing techniques like importance truncation or tensor factorisation.
Overall, the thesis work will exploit the latest advances in nuclear theory, including the use of nuclear interactions from chiral effective field theory and renormalisation group techniques, as well as high-performance computing codes and resources. The work will consist in formal developments, computational tasks and application of the new technology to cases of experimental interest. International collaborations are envisaged.
The theoretical description of atomic nuclei from first principles, or in a so-called ab initio fashion, has become possible only recently thanks to crucial advances in many-body theory and the availability of increasingly powerful high-performance computers. Such ab initio techniques are being successfully applied to study the structure of nuclei starting from the lighter isotopes. Still, extensions to heavy elements and nuclear reactions are posing considerable difficulties. The objective of the thesis is to contribute to this on-going progress in nuclear many-body theory. The project will focus on a developing ab initio technique (the so-called Gorkov-Green function approach, devised at CEA Saclay) designed to describe open-shell or superfluid systems (the majority of atomic nuclei). After the first promising applications to light and medium-mass nuclei, the method faces crucial upgrades to reach the precision and competitiveness of state-of-the-art approaches. The proposed work will aim to put in place the necessary tools towards this direction.
In particular, the Gorkov-Green function approach will be extended to the next level of precision. After some formal work, this will require a careful numerical implementation on top of the existing code. Given the increased cost of the corresponding numerical calculations, expected to go from moderately (100 proc.) to massively parallel (1000 proc.), special attention will have to be paid to the code optimisation and the use of pre-processing techniques like importance truncation or tensor factorisation.
Overall, the thesis work will exploit the latest advances in nuclear theory, including the use of nuclear interactions from chiral effective field theory and renormalisation group techniques, as well as high-performance computing codes and resources. The work will consist in formal developments, computational tasks and application of the new technology to cases of experimental interest. International collaborations are envisaged.
Study of reaction mechanisms for the synthesis of super-heavy elements
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Starting date : 01-10-2021
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Personal web page : https://www.ganil-spiral2.eu/wp-content/uploads/2020/09/SHEDYN-thesis2021.pdf
Laboratory link : https://www.ganil-spiral2.eu/fr/
One of the major research activities in nuclear physics is the study of nuclei at their limit of existence. These very exotic nuclei are expected to exhibit new properties, but are also very difficult to produce. The thesis deals with the study of nuclear reactions leading to the synthesis of super-heavy nuclei. The models are not accurate enough to guide experiments and there is little experimental data to constrain the models. The goal of this thesis is therefore to use innovative methods to constrain the models. It will consist in using state of the art statistical methods for low number data analysis as well as in designing experiments devoted to a better understanding of the reaction mechanisms involved.
Continuum QCD approaches and 3D structure of the nucleon
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=4189
Most of the visible mass of the universe is contained in nucleons. However, the origin of this mass remains mysterious, with the portion from the Higgs mechanism in standard renormalization schemes corresponding to only a few percent of the total mass. The answer is to be found in the dynamics of strong interaction, described by the theory of quantum chromodynamics (QCD) in terms of quarks and gluons. Thus, the interaction between quarks and gluons is responsible for the emergence of known and measured properties of hadrons such as their masses or spins.
There is now a strong theoretical and experimental dynamic to determine the 3D structure of hadrons in terms of quarks and gluons. From a theoretical point of view, the classical tools of quantum field theory, namely perturbative expansion, do not allow the study of the emerging properties of hadrons. The latter are inherently non- disruptive.
The aim of this thesis is to develop and use a non-perturbative formalism based on the Dyson-Schwinger and Bethe-Salpeter equations to determine the 3D structure of hadrons, in particular the nucleon. Different dynamic assumptions will be used to obtain a 3D mapping of the charge, mass and orbital angular momentum effects. To do so, a significant part of the Ph.D. will be dedicated to numerical development and analysis, in order to tackle different inverse problems. A comparison of the results obtained with the experimental data will be carried out in collaboration with the other LSN members.
There is now a strong theoretical and experimental dynamic to determine the 3D structure of hadrons in terms of quarks and gluons. From a theoretical point of view, the classical tools of quantum field theory, namely perturbative expansion, do not allow the study of the emerging properties of hadrons. The latter are inherently non- disruptive.
The aim of this thesis is to develop and use a non-perturbative formalism based on the Dyson-Schwinger and Bethe-Salpeter equations to determine the 3D structure of hadrons, in particular the nucleon. Different dynamic assumptions will be used to obtain a 3D mapping of the charge, mass and orbital angular momentum effects. To do so, a significant part of the Ph.D. will be dedicated to numerical development and analysis, in order to tackle different inverse problems. A comparison of the results obtained with the experimental data will be carried out in collaboration with the other LSN members.
3-dimensional scintillation dosimetry for small irradiation fields control in protontherapy
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Starting date : 01-10-2021
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Personal web page : https://www.ganil-spiral2.eu/wp-content/uploads/2020/09/SCICOPRO-thesis2021.pdf
Laboratory link : https://www.ganil-spiral2.eu/fr/
Radiotherapy is an important modality in treatment cancer. In this domain, proton beams have ballistic superiority against photon beams. Nevertheless, the use of protontherapy to treat small volume tumors (typically less than 27 cm3) is limited because of the lack of well adapted dosimetry tools for small irradiation fields quality assurance. To answer this issue, an innovative dosimetry system has been developed. It is based on a scintillating block of 10 × 10 × 10 cm3 and two ultra-fast cameras recording the scintillation from different points of view to reconstruct 3-dimensional dose maps. The current reconstruction method uses a library of preliminary beam measurements.
The objective of this PhD thesis will be to develop a new method directly converting scintillation maps into dose maps. This includes, in the first stage of the thesis, the study of the energy dependence of the scintillation yield with proton beams. The new reconstruction method will then be evaluated and compared to ionization chamber and dosimetry films measurements. Finally, the dosimetric system will be used to study dose uncertainties during treatment plan.
The objective of this PhD thesis will be to develop a new method directly converting scintillation maps into dose maps. This includes, in the first stage of the thesis, the study of the energy dependence of the scintillation yield with proton beams. The new reconstruction method will then be evaluated and compared to ionization chamber and dosimetry films measurements. Finally, the dosimetric system will be used to study dose uncertainties during treatment plan.
Short-range correlations in exotic nuclei
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Starting date : 01-10-2021
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Personal web page : http://irfu-i.cea.fr/Pisp/acorsi/
The atomic nucleus is a quantum system of correlated fermions, protons and neutrons. These can pair at very short distances (~1 fm, much less than their average distance), where the nuclear interaction becomes highly repulsive and is less well known. These configurations, called short-range correlations, give us a unique opportunity to study this regime in the laboratory. This regime is particularly critical since it is at the transition between a description of the nucleus in terms of protons/neutrons and quarks/gluons. Measurements to characterize short-range correlations have been performed in stable nuclei, but the measurement technique currently used does not allow us to study unstable nuclei, where the imbalance between neutrons and protons can affect these correlations. An experiment using a new technique which consists in sending the nucleus to be studied on a proton target is the subject of this thesis.
Prompt and non-prompt quarkonium production in the Pb-Pb collisions at 5 TeV of the LHC Run 3
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=500
More : https://alice-collaboration.web.cern.ch
A few micro-seconds after the Big Bang, the Universe was in a quark gluon plasma (QGP) state. Such state is predicted by Quantum Chromodynamics, which is the theory of strong interactions, and should be reached at very high temperature or energy density. Such conditions are reproduced in ultra-relativistic heavy ion collisions at the LHC at CERN.
Among the various QGP observables, the study of hadrons with heavy-flavour quarks (charm c or beauty b) and quarkonia (c-cbar or b-bbar bound states) is particularly important to understand the properties of the QGP.
Quarkonia are rare and heavy particles which are produced in the initial stages of the collision even before the QGP is formed, mainly through gluon-fusion processes, and are therefore ideal probes of the QGP. As they traverse the QGP, the quark/anti-quarks pair will get screened by the many free quarks and gluons of the QGP. Quarkonia will then be suppressed by a colour screening mechanism in the QGP. Since the various quarkonium states have different binding energies, each state will have a different probability of being dissociated. This results in a sequential suppression pattern of the quarkonium states. Additionally, if the initial number of produced quark/anti-quark pairs is large and if heavy quarks do thermalise in the QGP, then new quarkonia could be produced in the QGP by recombination of heavy quarks. This mechanism is known as regeneration. At the LHC, Upsilon (b-bbar) and J/psi (c-cbar) are complementary. The former are thought to be more suited than to address the sequential suppression, while the latter should allow to study possible regeneration mechanisms. In addition, non-prompt J/psi, i.e. from weak decays hadrons containing one valance b quark, give access to the transport properties of b quarks in the QGP. More recently, photoproduction of J/psi has been observed in peripheral Pb-Pb collisions; J/psi are produced from the photon flux of the moving Pb ions mostly at very low transverse momenta. The characterization of these photoproduced quarkonia would allow to better constrain the initial state of the collisions as well as the properties of the QGP.
We propose to study the production of prompt and non-prompt quarkonia Pb-Pb collisions at a center-of-mass energy per nucleon pair (sqrt(sNN)) of 5 TeV at the LHC with the first data of Run 3 (2022-2024). An upgrade of the ALICE apparatus is ongoing with, in particular, the addition of silicon pixel tracker that will complement the ALICE forward spectrometer as well as new readout electronics for the latter. These upgrades will allow us to: Profit from the planned increase in luminosity of the LHC, thus tripling in one year the data collected in the full LHC Run 2 (2015-2018); Separate the prompt and non-prompt contributions thanks to the precise measurement of the quarkonium decay vertex into two muons.
The student will first develop the procedures to separate prompt and non-prompt quarkonia. In doing so, the student will thus contribute to the development of the new software for data reconstructions, simulation, calibration and analysis that the ALICE Collaboration is developing for Runs 3 and 4 of the LHC. Secondly, the student will study the production of prompt and non-prompt quarkonia in terms of production yields and azimuthal anisotropy. These studies could be performed as a function of the centrality of the collision and transverse momentum and rapidity of the quarkonia, for various types of quarkonia. Depending on the progress of the thesis work, these studies, which are a priority for quarkonia produced by the hadronic collision, could be extended to photoproduced quarkonia.
Among the various QGP observables, the study of hadrons with heavy-flavour quarks (charm c or beauty b) and quarkonia (c-cbar or b-bbar bound states) is particularly important to understand the properties of the QGP.
Quarkonia are rare and heavy particles which are produced in the initial stages of the collision even before the QGP is formed, mainly through gluon-fusion processes, and are therefore ideal probes of the QGP. As they traverse the QGP, the quark/anti-quarks pair will get screened by the many free quarks and gluons of the QGP. Quarkonia will then be suppressed by a colour screening mechanism in the QGP. Since the various quarkonium states have different binding energies, each state will have a different probability of being dissociated. This results in a sequential suppression pattern of the quarkonium states. Additionally, if the initial number of produced quark/anti-quark pairs is large and if heavy quarks do thermalise in the QGP, then new quarkonia could be produced in the QGP by recombination of heavy quarks. This mechanism is known as regeneration. At the LHC, Upsilon (b-bbar) and J/psi (c-cbar) are complementary. The former are thought to be more suited than to address the sequential suppression, while the latter should allow to study possible regeneration mechanisms. In addition, non-prompt J/psi, i.e. from weak decays hadrons containing one valance b quark, give access to the transport properties of b quarks in the QGP. More recently, photoproduction of J/psi has been observed in peripheral Pb-Pb collisions; J/psi are produced from the photon flux of the moving Pb ions mostly at very low transverse momenta. The characterization of these photoproduced quarkonia would allow to better constrain the initial state of the collisions as well as the properties of the QGP.
We propose to study the production of prompt and non-prompt quarkonia Pb-Pb collisions at a center-of-mass energy per nucleon pair (sqrt(sNN)) of 5 TeV at the LHC with the first data of Run 3 (2022-2024). An upgrade of the ALICE apparatus is ongoing with, in particular, the addition of silicon pixel tracker that will complement the ALICE forward spectrometer as well as new readout electronics for the latter. These upgrades will allow us to: Profit from the planned increase in luminosity of the LHC, thus tripling in one year the data collected in the full LHC Run 2 (2015-2018); Separate the prompt and non-prompt contributions thanks to the precise measurement of the quarkonium decay vertex into two muons.
The student will first develop the procedures to separate prompt and non-prompt quarkonia. In doing so, the student will thus contribute to the development of the new software for data reconstructions, simulation, calibration and analysis that the ALICE Collaboration is developing for Runs 3 and 4 of the LHC. Secondly, the student will study the production of prompt and non-prompt quarkonia in terms of production yields and azimuthal anisotropy. These studies could be performed as a function of the centrality of the collision and transverse momentum and rapidity of the quarkonia, for various types of quarkonia. Depending on the progress of the thesis work, these studies, which are a priority for quarkonia produced by the hadronic collision, could be extended to photoproduced quarkonia.
Is there a dark decay of neutrons in 6He ?
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Starting date : 01-10-2021
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Personal web page : https://www.ganil-spiral2.eu/wp-content/uploads/2020/09/NDD-thesis2021.pdf
Recently, two theoretical physicists put forward a thrilling hypothesis: neutrons may undergo a dark matter decay mode. Such a decay could explain the existing discrepancy of 4 standard deviations between two different methods of neutron lifetime measurements. If such a neutron decay is possible, then it could also occur in nuclei with sufficiently low neutron binding energy, a quasifree neutron decay. In this work, we consider the case of 6He with a two-neutron separation energy lower than the one for a single neutron. The observation of a free neutron from 6He decay would, although difficult to do, be a unique signature for the dark neutron decay.
Towards super heavy elements: new paths for the study of heavy nuclei
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Starting date : 01-10-2021
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Hunting for super heavy elements one of the most exciting and active topics during the last few years and has already produced new elements such as 113, 115, 117 and 118 in accelerator experiments. All these nuclei can be produced through fusion-evaporation reactions. However their studies are greatly hampered by the extremely low production rates, hence experimental information in this region is very scarce. The high-intensity stable beams of the superconducting linear accelerator of the SPIRAL2 facility at GANIL coupled with the Super Separator Spectrometer (S3) and a high-performance focal-plane spectrometer (SIRIUS) will open new horizons for the research in the domains of such rare nuclei and low cross-section phenomena at the limit of nuclear stability. The student will take an active part in the tests of the whole SIRIUS detector.
Information on the heaviest elements have been obtained up to now via fusion evaporation reactions. It is however well known that the only nuclei one can reach using fusion-evaporation reactions are neutron deficient and moreover in a very limited number (because of the limited number of beam-target combinations). An alternative to fusion-evaporation could be a revolutionary method based on be deep-inelastic collisions. The student will take, therefore, an active part in the new scientific activities of the group having as primary aim the investigation of nuclear structure in the heavy elements employing the new alternative method using multi-nucleon transfer reactions.
Information on the heaviest elements have been obtained up to now via fusion evaporation reactions. It is however well known that the only nuclei one can reach using fusion-evaporation reactions are neutron deficient and moreover in a very limited number (because of the limited number of beam-target combinations). An alternative to fusion-evaporation could be a revolutionary method based on be deep-inelastic collisions. The student will take, therefore, an active part in the new scientific activities of the group having as primary aim the investigation of nuclear structure in the heavy elements employing the new alternative method using multi-nucleon transfer reactions.
Study and Modeling of an axisymmetric electron cyclotron resonance ion source
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Starting date : 01-10-2021
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Personal web page : https://www.ganil-spiral2.eu/wp-content/uploads/2020/09/EMIRA-thesis2021.pdf
Laboratory link : https://www.ganil-spiral2.eu/fr/
GANIL has a long tradition in the use and development of low-pressure off-balance ion sources based on the Electron Cyclotron Resonance (ECR) process feeding the GANIL accelerators with highly charged ions. One of the challenge of this type of sources used upstream of the accelerator is to deliver high charge state ions at high intensity specifically for the production of metal ions. An early simulation tool (PhD Thesis of Alexandre Leduc) has been developed to better understand how the ECR Phoenix V3 source operates. This work has already led to the understanding of some limitations of these sources, but a step forward must be done to obtain more realistic modelling of an ECR plasma: include electron dynamics and the creation of self-consistent electrostatic potentials essential for the production of multicharged ions. Before achieving that, an intermediate milestone will be done by developing the simulation tools on an axisymmetric ECR ion source before extending them to a standard ECR ion source.
Study of drip-line phenomena in neutron-rich nuclei
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Starting date : 01-10-2021
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Personal web page : https://www.ganil-spiral2.eu/wp-content/uploads/2020/09/SHARP-thesis2021.pdf
Laboratory link : https://www.ganil-spiral2.eu/fr/
The present project aims at better understanding the nuclear superfluidity of atomic nuclei, which manifests for instance in a smaller moment of inertia as compared to a rigid body, deduced from their rotational or vibrational spectra. Superfluidity is thought to be induced by the pairing of nucleons, but the size of the pairs, their evolution as a function of the atomic mass and of the binding energy, or with shell structure are not known. Moreover, superfluidity may be caused by a larger number of correlated nucleons, such as quartets. These properties of the atomic nucleus are almost impossible to study as nucleons are bound inside a nuclear potential. We have proposed an innovative route to suddenly promote neutron pairs or quartets out of the nuclear potential and study the correlations they had inside the nucleus from the observation of their many-body decay. The experimental strategy is to use the instrumentation of the R3B beam line at FAIR which offers the unique possibility to measure all relevant information, such as neutrons and residual nucleus momenta, to study nuclear superfluidity and its possible change of regime towards the neutron drip line.
Systematic studies of the continuum-coupling correlations in near-threshold states
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Starting date : 01-10-2021
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Personal web page : https://www.ganil-spiral2.eu/wp-content/uploads/2020/09/GSM21-thesis2021.pdf
Laboratory link : https://www.ganil-spiral2.eu/fr/
It is proposed to study the salient effects of coupling between discrete and continuous states near various particle emission thresholds using the shell model in the complex energy plane. This model provides the unitary formulation of a standard shell model within the framework of the open quantum system for the description of well bound, weakly bound and unbound nuclear states.
Recent studies have demonstrated the importance of the residual correlation energy of coupling to the states of the continuum for the understanding of eigenstates, their energy and decay modes, in the vicinity of the reaction channels. This residual energy has not yet been studied in detail. The studies of this thesis will deepen our understanding of the structural effects induced by coupling to the continuum and will support for experimental studies at GANIL and elsewhere. The student of this theoretical thesis will develop the numerical tools necessary for the evolution of the "Gamow Shell Model" (GSM), a tool par excellence for spectroscopic studies.
Recent studies have demonstrated the importance of the residual correlation energy of coupling to the states of the continuum for the understanding of eigenstates, their energy and decay modes, in the vicinity of the reaction channels. This residual energy has not yet been studied in detail. The studies of this thesis will deepen our understanding of the structural effects induced by coupling to the continuum and will support for experimental studies at GANIL and elsewhere. The student of this theoretical thesis will develop the numerical tools necessary for the evolution of the "Gamow Shell Model" (GSM), a tool par excellence for spectroscopic studies.
DETECTORS FOR TIME-OF-FLIGHT PET IMAGING WITH HIGH SPATIAL RESOLUTION
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Starting date : 01-10-2021
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Personal web page : http://irfu.cea.fr/Pisp/dominique.yvon/
Laboratory link : http://irfu.cea.fr/dedip/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3730
DESCRIPTION
Positron emission tomography (PET) is a nuclear imaging technique widely used in oncology and neurobiological research. Decay of the radioactive tracer emits positrons, which annihilate in the nearby tissue. Two gamma quanta of 511 keV energy are produced by positron annihilation and allow one to reconstruct the annihilation vertex and distribution of the tracer activity in the body of the patient.
The precise determination of the position of the positron annihilation vertex is important for an accurate image reconstruction with a good contrast. In particular, it is useful for neuroimaging studies of brain and for pre-clinical studies with animal models (rodents) as well as for full body PET imaging. In this thesis we propose to contribute to an ambitious detector based on Cherenkov/Scintillating crystals. We have selected technologies that are particularly effective for PET imaging. The principles of the detector are patented. They should allow one to produce PET scanner with highly improved performances. The device uses advanced particles detector technologies: a dense scintillator crystal, micro-channel plate photomultipliers, gigahertz bandwidth amplifiers and fast data acquisition modules (WaveCatcher, SAMPIC). Data processing will involve Monté-Carlo simulations and data analysis based on GATE/Geant4 and Root C++ software libraries.
SUPERVISION
The successful candidate will work in the Department of Particle Physics of IRFU in close collaboration with the Department of Electronics Detectors and Computer Science for Physics. The CaLIPSO group includes two physicists and two students. Two Postdoc will join the project next spring. We collaborate closely with CNRS- IJCLabs on fast readout electronic, with CPPM of Marseille and CEA-SHFJ, and CEA-DES for simulations of medical imaging devices and image reconstruction algorithms, and with the University of Munster (Germany).
THE PROPOSED WORK
You will calibrate and optimize the detector prototypes and analyze the measured data. Your work will be focussing on detector time and spatial resolution optimization. This will involve many skills of an instrument scientist : fast photo-detection, fast electronics read-out (analog and digital) with picosecond precision, hardware and detector simulations with GEANT4 and GATE software.
REQUIREMENTS
Knowledge in physics, particle interactions with matter, radioactivity and particle detector principles, a vocation for instrumental (hardware) work, data analysis are mandatory. Being comfortable in programming, having a background in Gate/Geant4 simulation and C++ will be an asset.
ACQUIRED SKILLS
You will acquire skills in particle detector instrumentation, simulation of ionizing radiation detectors, photo-detection, implementation, operation of fast digitizing electronics, and data analysis.
Positron emission tomography (PET) is a nuclear imaging technique widely used in oncology and neurobiological research. Decay of the radioactive tracer emits positrons, which annihilate in the nearby tissue. Two gamma quanta of 511 keV energy are produced by positron annihilation and allow one to reconstruct the annihilation vertex and distribution of the tracer activity in the body of the patient.
The precise determination of the position of the positron annihilation vertex is important for an accurate image reconstruction with a good contrast. In particular, it is useful for neuroimaging studies of brain and for pre-clinical studies with animal models (rodents) as well as for full body PET imaging. In this thesis we propose to contribute to an ambitious detector based on Cherenkov/Scintillating crystals. We have selected technologies that are particularly effective for PET imaging. The principles of the detector are patented. They should allow one to produce PET scanner with highly improved performances. The device uses advanced particles detector technologies: a dense scintillator crystal, micro-channel plate photomultipliers, gigahertz bandwidth amplifiers and fast data acquisition modules (WaveCatcher, SAMPIC). Data processing will involve Monté-Carlo simulations and data analysis based on GATE/Geant4 and Root C++ software libraries.
SUPERVISION
The successful candidate will work in the Department of Particle Physics of IRFU in close collaboration with the Department of Electronics Detectors and Computer Science for Physics. The CaLIPSO group includes two physicists and two students. Two Postdoc will join the project next spring. We collaborate closely with CNRS- IJCLabs on fast readout electronic, with CPPM of Marseille and CEA-SHFJ, and CEA-DES for simulations of medical imaging devices and image reconstruction algorithms, and with the University of Munster (Germany).
THE PROPOSED WORK
You will calibrate and optimize the detector prototypes and analyze the measured data. Your work will be focussing on detector time and spatial resolution optimization. This will involve many skills of an instrument scientist : fast photo-detection, fast electronics read-out (analog and digital) with picosecond precision, hardware and detector simulations with GEANT4 and GATE software.
REQUIREMENTS
Knowledge in physics, particle interactions with matter, radioactivity and particle detector principles, a vocation for instrumental (hardware) work, data analysis are mandatory. Being comfortable in programming, having a background in Gate/Geant4 simulation and C++ will be an asset.
ACQUIRED SKILLS
You will acquire skills in particle detector instrumentation, simulation of ionizing radiation detectors, photo-detection, implementation, operation of fast digitizing electronics, and data analysis.
Testing nuclear interaction at the dripline
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Starting date : 01-10-2021
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The exploration of nuclei close to the limit of their existence (called dripline) offers the unique opportunity to observe and study many phenomena not - or insufficiently - predicted by theory such as the appearance of neutron "halos" as well as the emergence of new magic numbers and the disappearance of those observed in nuclei close to stability.
The proposed thesis topic revolves around the study of these emerging phenomena in exotic nuclei (see beyond dripline) via the analysis of data from experiments carried out in RIKEN (Japan) and using the state-of-the-art experimental devices SAMURAI and MINOS which are key for the study of these phenomena.
The proposed thesis topic revolves around the study of these emerging phenomena in exotic nuclei (see beyond dripline) via the analysis of data from experiments carried out in RIKEN (Japan) and using the state-of-the-art experimental devices SAMURAI and MINOS which are key for the study of these phenomena.
Studies on neutron-induced reactions with MEDLEY at GANIL.
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Starting date : 01-10-2021
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Personal web page : https://www.ganil-spiral2.eu
This thesis is devoted to the study of nuclear reactions induced by neutrons between 15 and 40 MeV at the NFS facility using the Medley detector. The double differential cross sections of light charged particles emitted during reactions on carbon and chromium will be measured in order to enrich databases and improve certain reaction codes. The fission cross sections of uranium 235 and 238, which are standards, will also be measured relatively to the elastic diffusion cross section on hydrogen.
INVESTIGATION OF THE NUCLEAR TWO-PHOTON DECAY IN SWIFT FULLY STRIPPED HEAVY IONS
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Starting date : 01-10-2021
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Personal web page : https://www.researchgate.net/profile/Wolfram_Korten
Laboratory link : http://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_sstheme.php?id_ast=293
More : https://www.gsi.de/en/work/research/appamml/atomic_physics/experimental_facilities/esr.htm
The nuclear two-photon, or double-gamma decay is a rare decay mode in atomic nuclei whereby a nucleus in an excited state emits two gamma rays simultaneously. Even-even nuclei with a first excited 0+ state are favorable cases to search for a double-gamma decay branch, since the emission of a single gamma ray is strictly forbidden for 0+ ? 0+ transitions by angular momentum conservation. The double-gamma decay still remains a very small decay branch (<1E-4) competing with the dominant (first-order) decay modes of atomic internal-conversion electrons (ICE) or internal positron-electron (e+-e-) pair creation (IPC). Therefore we will make use of a new technique to search for the double-gamma decay in bare (fully-stripped) ions, which are available at the GSI facility in Darmstadt, Germany. The basic idea of our experiment is to produce, select and store exotic nuclei in their excited 0+ state in the GSI storage ring (ESR). For neutral atoms the excited 0+ state is a rather short-lived isomeric state with a lifetime of the order of a few tens to hundreds of nanoseconds. At relativistic energies available at GSI, however, all ions are fully stripped of their atomic electrons and decay by ICE emission is hence not possible. If the state of interest is located below the pair creation threshold the IPC process is not possible either. Consequently, bare nuclei are trapped in a long-lived isomeric state, which can only decay by double-gamma emission to the ground state. The decay of the isomers would be identified by so-called time-resolved Schottky Mass Spectroscopy. This method allows to distinguish the isomer and the ground state state by their (very slightly) different revolution time in the ESR, and to observe the disappearance of the isomer peak in the mass spectrum with a characteristic decay time. An experiment to search for the double-gamma decay in 72Ge and 70Se has already been accepted by the GSI Programme Committee and should be realised in 2021/22.
FIssion Studies at VAMOS in Inverse Kinematics (FISVIK)
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Starting date : 01-10-2021
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Personal web page : https://www.ganil-spiral2.eu/wp-content/uploads/2020/09/GSM21-thesis2021.pdf
The nuclear fission process is driven by a complex interplay between the dynamical evolution of a quantum system composed of a large number of nucleons and the intrinsic nuclear structure of the system at extreme deformations as well as heat flows. The balance between these various aspects decide the characteristics of the emerging fragments. Innovative experiments are conducted to widen
STUDY OF THE RARE DECAY OF THE HGGS BOSON TO A PAIR OF MUONS WITH THE ATLAS DETECTOR AT THE LHC
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Starting date : 01-09-2021
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In July 2012, the ATLAS and CMS collaborations announced the discovery of a new particle with a mass of about 125 GeV, at the Large Hadron Collider (LHC) at CERN. Since this discovery, the two collaborations have been actively studying the properties of this new particle, so far consistent with those of the Standard Model Higgs boson.
In the Standard Model, the Brout-Englert-Higgs mechanism predicts that the Higgs boson will interact with particles of matter (quarks and leptons, called fermions) with a force proportional to the mass of the particle. It also predicts the Higgs boson will interact with the force carrier particles (W and Z bosons) with a strength proportional to the square of the particle's mass. Therefore, by measuring the Higgs boson decay and production rates, which depend on the interaction strength to these other particles, one can perform a fundamental test of the Standard Model.
The ATLAS and CMS collaborations have already observed the decay of the Higgs boson into tau lepton, belonging to the third “generation” of fermions. Since muons are much lighter than tau leptons, the decay of the Higgs boson into a muon pair is expected to occur about 300 times less often than that of a lepton-tau pair. Despite this scarceness, the H ? µµ decay provides the best opportunity to measure the interaction of the Higgs boson with second generation fermions at the LHC, providing new information on the origin of mass for different generations of fermions. The ATLAS and CMS collaborations recently presented results on this decay using the dataset during the 2nd phase of the LHC (Run-2 from 2015 to 2018). Figure 1 shows the mass distribution of muon pairs while Figure 2 shows an example of a candidate event to be a Higgs boson decaying into two muons as recorded by the ATLAS detector. The study of this process is one of the main objectives of the third phase of the LHC (Run-3).
The aim of this thesis is the search for a Higgs boson decaying into two muons by analyzing the whole dataset from Run-3 and combining them with the previous data from the second phase (Run-2) in order to establish the discovery of the decay of the Higgs boson into two muons and constrain possible theories of physics beyond the Standard Model that would affect this decay mode of the Higgs boson. The thesis will also include work on the performance evaluation of the ATLAS muon spectrometer. Particular interest will be paid to the understanding, analysis and operation of MicroMegas type gas detectors. The purpose of phase-I of the ATLAS detector upgrade is to prepare for the high luminosities that will supply the LHC. In this context, the 2 large detection planes called NSW (New Small Wheel) will be equipped with new MicroMegas type detectors and will replace part of the ATLAS muon spectrometer and be operational for the restart of the LHC in 2022.
In the Standard Model, the Brout-Englert-Higgs mechanism predicts that the Higgs boson will interact with particles of matter (quarks and leptons, called fermions) with a force proportional to the mass of the particle. It also predicts the Higgs boson will interact with the force carrier particles (W and Z bosons) with a strength proportional to the square of the particle's mass. Therefore, by measuring the Higgs boson decay and production rates, which depend on the interaction strength to these other particles, one can perform a fundamental test of the Standard Model.
The ATLAS and CMS collaborations have already observed the decay of the Higgs boson into tau lepton, belonging to the third “generation” of fermions. Since muons are much lighter than tau leptons, the decay of the Higgs boson into a muon pair is expected to occur about 300 times less often than that of a lepton-tau pair. Despite this scarceness, the H ? µµ decay provides the best opportunity to measure the interaction of the Higgs boson with second generation fermions at the LHC, providing new information on the origin of mass for different generations of fermions. The ATLAS and CMS collaborations recently presented results on this decay using the dataset during the 2nd phase of the LHC (Run-2 from 2015 to 2018). Figure 1 shows the mass distribution of muon pairs while Figure 2 shows an example of a candidate event to be a Higgs boson decaying into two muons as recorded by the ATLAS detector. The study of this process is one of the main objectives of the third phase of the LHC (Run-3).
The aim of this thesis is the search for a Higgs boson decaying into two muons by analyzing the whole dataset from Run-3 and combining them with the previous data from the second phase (Run-2) in order to establish the discovery of the decay of the Higgs boson into two muons and constrain possible theories of physics beyond the Standard Model that would affect this decay mode of the Higgs boson. The thesis will also include work on the performance evaluation of the ATLAS muon spectrometer. Particular interest will be paid to the understanding, analysis and operation of MicroMegas type gas detectors. The purpose of phase-I of the ATLAS detector upgrade is to prepare for the high luminosities that will supply the LHC. In this context, the 2 large detection planes called NSW (New Small Wheel) will be equipped with new MicroMegas type detectors and will replace part of the ATLAS muon spectrometer and be operational for the restart of the LHC in 2022.
CALIBRATION OF BOLOMETERS AT THE KeV SCALE AND NEUTRINO COHERENT SCATTERING WITH THE NUCLEUS EXPERIMENT
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_sstheme.php?id_ast=31&voir=technique
The central topic of this thesis is the NUCLEUS experiment, whose motivation is to measure the coherent scattering of neutrinos emitted by the reactors of the EDF power plant at Chooz, in the Ardennes. Although, in the MeV energy range that concerns us, coherent scattering on nuclei is the most probable mode of interaction of neutrinos with matter, it is extremely difficult to detect because its only signature is the tiny recoil of the target nucleus. Thus the first observation of this process dates from 2017 only, with neutrinos of a few 10 MeV from the Oak Ridge spallation source. Measurements at the reactors have yet to be made, and NUCLEUS aims to carry out a precise study of this as yet unexplored neutrino-matter coupling, with a unique sensitivity to potential new physics in the electroweak sector of the standard model. Coherent scattering differs from the beta-inverse reaction used up to now by an interaction cross section several orders of magnitude higher allowing a miniaturization of the detectors: only 10g of target for the first phase of NUCLEUS. Finally, the absence of a reaction threshold (instead of 1.8 MeV for the beta-inverse reaction) could also allow direct monitoring of the accumulation of plutonium in the nuclear reactor cores.
NUCLEUS will use sapphire (Al2O3) and calcium tungstate (CaWO4) bolometers in the form of 5 mm edge cubic crystals. A detection threshold of 20 eV has already been reached with this technology. The thesis work proposed here will focus on two central aspects of the experiment: the calibration of the detectors and the rejection of cosmic rays, the main source of background. An accurate calibration is indeed crucial to study coherent scattering and to reach the best sensitivity on a potential new physics. Although the energy range of the expected nuclear recoils, of the order of 100 eV, is above the achieved detection thresholds, no absolute calibration method for bolometers currently exists for this new region of interest. The extrapolation of the available measurements from the keV scale is problematic due to a rapid and non-trivial evolution of the contribution of the different excitation modes: phonons, ionization and scintillation. A new method proposed by the Department of Nuclear Physics of CEA-Saclay (DPhN) would give access for the first time to calibrated nuclear recoils, in the 100 eV range and uniformly distributed in the volume of the bolometer. The validation of this method and a first measurement with a NUCLEUS bolometer will be developed during the thesis, in collaboration with the IJCLab d'Orsay, the University of Munich (TUM) and the University of Vienna (TU Wien). Applicable to different types of bolometers, this method has potentially a strong scientific impact towards coherent neutrino scattering programs, light dark matter research but also solid state physics.
DPhN is also heavily involved in the development of the NUCLEUS muon veto. This active shielding surrounds as hermetically as possible the central detectors with plastic scintillator panels whose light is extracted by optical fibers connected to Silicon-Photomultipliers (SiPM). Its purpose is to sign the passage of cosmic rays near the bolometers in order to reject any event (potentially background) during the next ~100 microseconds. Data from this detector is a natural input to the NUCLEUS analysis. The start of the data collection on EDF site is planned for the end of 2022 - beginning of 2023.
Finally, the DPhN is also at the origin of the STEREO experiment which is motivated by the search for sterile neutrinos and the precise measurement of the neutrino spectrum resulting from the fission of 235U. It is installed at the ILL research reactor and is completing its data collection this year. Part of the thesis work could be oriented towards combining the final results of STEREO with those of other neutrino experiments, an effort already started with the PROSPECT collaboration. Some of the techniques involved in spectrum unfolding and global fit could be transferable to NUCLEUS.
Organization of the work:
The priority at the beginning of the thesis will be put on the development of the calibration method for 100 eV bolometers with a first step of proof of concept at CEA and Orsay in 2021-22, then a measurement with the a NUCLEUS bolometer in Germany in 2022-23. This work should lead to several publications.
Involvement in the analysis of NUCLEUS data will be stepped up in the second part of the thesis. The entry point will be the exploitation of data from the muon veto, installed on the EDF site from the end of 2022. The first work will be the optimization of gains and thresholds for each SiPM in order to ensure a high rejection of ambient gamma rays, a high muon detection efficiency and a controlled acquisition dead time. An automatic monitoring of the evolution in time of the performances will be set up. Then further analysis will focus on a specific source of background generated by cosmic rays.
In connection with the work on the calibration of bolometers, sensitivity studies could be carried out within the framework of low energy tests of the standard model accessible by NUCLEUS: evolution of sin2_theta_W, magnetic moment of the neutrino ... A synergy with some developments of the final analysis of STEREO would then be exploitable.
Through this work the student will have a complete training as an experimental physicist with aspects of simulation, detector development and data analysis. The physics topics addressed, coherent neutrino scattering and bolometer calibration, are very active in the community and will offer many research perspectives at the end of the thesis. The student will evolve in international collaborations. Within the CEA he (she) will benefit from the "transverse" character of the neutrino and will be in regular interaction with the nuclear physics, particle physics and reactor physics communities.
NUCLEUS will use sapphire (Al2O3) and calcium tungstate (CaWO4) bolometers in the form of 5 mm edge cubic crystals. A detection threshold of 20 eV has already been reached with this technology. The thesis work proposed here will focus on two central aspects of the experiment: the calibration of the detectors and the rejection of cosmic rays, the main source of background. An accurate calibration is indeed crucial to study coherent scattering and to reach the best sensitivity on a potential new physics. Although the energy range of the expected nuclear recoils, of the order of 100 eV, is above the achieved detection thresholds, no absolute calibration method for bolometers currently exists for this new region of interest. The extrapolation of the available measurements from the keV scale is problematic due to a rapid and non-trivial evolution of the contribution of the different excitation modes: phonons, ionization and scintillation. A new method proposed by the Department of Nuclear Physics of CEA-Saclay (DPhN) would give access for the first time to calibrated nuclear recoils, in the 100 eV range and uniformly distributed in the volume of the bolometer. The validation of this method and a first measurement with a NUCLEUS bolometer will be developed during the thesis, in collaboration with the IJCLab d'Orsay, the University of Munich (TUM) and the University of Vienna (TU Wien). Applicable to different types of bolometers, this method has potentially a strong scientific impact towards coherent neutrino scattering programs, light dark matter research but also solid state physics.
DPhN is also heavily involved in the development of the NUCLEUS muon veto. This active shielding surrounds as hermetically as possible the central detectors with plastic scintillator panels whose light is extracted by optical fibers connected to Silicon-Photomultipliers (SiPM). Its purpose is to sign the passage of cosmic rays near the bolometers in order to reject any event (potentially background) during the next ~100 microseconds. Data from this detector is a natural input to the NUCLEUS analysis. The start of the data collection on EDF site is planned for the end of 2022 - beginning of 2023.
Finally, the DPhN is also at the origin of the STEREO experiment which is motivated by the search for sterile neutrinos and the precise measurement of the neutrino spectrum resulting from the fission of 235U. It is installed at the ILL research reactor and is completing its data collection this year. Part of the thesis work could be oriented towards combining the final results of STEREO with those of other neutrino experiments, an effort already started with the PROSPECT collaboration. Some of the techniques involved in spectrum unfolding and global fit could be transferable to NUCLEUS.
Organization of the work:
The priority at the beginning of the thesis will be put on the development of the calibration method for 100 eV bolometers with a first step of proof of concept at CEA and Orsay in 2021-22, then a measurement with the a NUCLEUS bolometer in Germany in 2022-23. This work should lead to several publications.
Involvement in the analysis of NUCLEUS data will be stepped up in the second part of the thesis. The entry point will be the exploitation of data from the muon veto, installed on the EDF site from the end of 2022. The first work will be the optimization of gains and thresholds for each SiPM in order to ensure a high rejection of ambient gamma rays, a high muon detection efficiency and a controlled acquisition dead time. An automatic monitoring of the evolution in time of the performances will be set up. Then further analysis will focus on a specific source of background generated by cosmic rays.
In connection with the work on the calibration of bolometers, sensitivity studies could be carried out within the framework of low energy tests of the standard model accessible by NUCLEUS: evolution of sin2_theta_W, magnetic moment of the neutrino ... A synergy with some developments of the final analysis of STEREO would then be exploitable.
Through this work the student will have a complete training as an experimental physicist with aspects of simulation, detector development and data analysis. The physics topics addressed, coherent neutrino scattering and bolometer calibration, are very active in the community and will offer many research perspectives at the end of the thesis. The student will evolve in international collaborations. Within the CEA he (she) will benefit from the "transverse" character of the neutrino and will be in regular interaction with the nuclear physics, particle physics and reactor physics communities.
MEASUREMENT OF VECTOR-BOSON SCATTERING WITH THE ATLAS DETECTOR AT THE LHC
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Starting date : 01-09-2021
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The vector-boson scattering process, pp?VV+jj+X, where V=W,Z, is characterized by the presence of
leptons from the W or Z decay, and high-energy forward jets in the final state. WW, WZ and ZZ scattering all have
been observed during the LHC Run2, with partial
datasets. The next step for the community in this field, using improved event selections and event classification, and larger data samples, is to enhance the visibility of the signal and confront the SM predictions with more precise analysis results.
This measurement constitutes a fundamental test of the coupling between the Higgs and the vector bosons, and of the Standard Model as whole.
leptons from the W or Z decay, and high-energy forward jets in the final state. WW, WZ and ZZ scattering all have
been observed during the LHC Run2, with partial
datasets. The next step for the community in this field, using improved event selections and event classification, and larger data samples, is to enhance the visibility of the signal and confront the SM predictions with more precise analysis results.
This measurement constitutes a fundamental test of the coupling between the Higgs and the vector bosons, and of the Standard Model as whole.
Z boson precision physics with the Atlas detector at LHC
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Starting date : 01-09-2021
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Laboratory link : http://irfu.cea.fr/Spp/index.php
The thesis will start in Autumn 2021. ATLAS, one of the major experiment at the LHC, is preparing for the expected increase of luminosity for Run3 and HL-LHC. The first part of the thesis is dedicated to a qualification task that could either consist in participating to the commissioning of the new muon detectors which are integrating the experiment, or taking part in the muon momentum calibration effort in view of Run3, that will start in 2022. Both options are closely related to the main thesis subject. The thesis will be followed by a measurement of precision physics in the field of the Z boson with ATLAS data.
The subject is focused on electroweak precision physics in ATLAS. The aim is to measure with the best possible precision the electroweak mixing angle, as well as the mass of the Z boson, using Run2 and Run3 data. The explored channel is that of the Z boson decaying into a muon-antimuon lepton pair. The student will work on muon momentum calibration using the J/Psi resonance as a standard candle, and will also reduce, through advanced fitting methods, the uncertainties related to the parton distributions functions (PDFs). These measurements should lead to a high improvement in the electroweak fit and thus significantly constrain the Standard Model, as well as Beyond Standard Model physics.
The CEA ATLAS group is part of the Department of Particle Physics (DPhP) of the Institute of Research into the Fundamental Laws of the Universe (IRFU) at CEA Paris-Saclay.
DPhP comprises about 110 physicists. DPhP scientific themes include elementary components of matter at the highest energies at the CERN LHC collider, R&D for future accelerators, study of antimatter, neutrino physics, gamma ray astronomy, study of gravitational waves, observational cosmology and instrumentation for medical applications. The group has a world-leading expertise in electroweak physics, namely with measurements of Z, W and Higgs boson cross sections and measurement of the W boson mass, achieved for the first time at the LHC. It builds on competences in muon reconstruction and muon spectrometer alignment and electron/photon identification.
The subject is focused on electroweak precision physics in ATLAS. The aim is to measure with the best possible precision the electroweak mixing angle, as well as the mass of the Z boson, using Run2 and Run3 data. The explored channel is that of the Z boson decaying into a muon-antimuon lepton pair. The student will work on muon momentum calibration using the J/Psi resonance as a standard candle, and will also reduce, through advanced fitting methods, the uncertainties related to the parton distributions functions (PDFs). These measurements should lead to a high improvement in the electroweak fit and thus significantly constrain the Standard Model, as well as Beyond Standard Model physics.
The CEA ATLAS group is part of the Department of Particle Physics (DPhP) of the Institute of Research into the Fundamental Laws of the Universe (IRFU) at CEA Paris-Saclay.
DPhP comprises about 110 physicists. DPhP scientific themes include elementary components of matter at the highest energies at the CERN LHC collider, R&D for future accelerators, study of antimatter, neutrino physics, gamma ray astronomy, study of gravitational waves, observational cosmology and instrumentation for medical applications. The group has a world-leading expertise in electroweak physics, namely with measurements of Z, W and Higgs boson cross sections and measurement of the W boson mass, achieved for the first time at the LHC. It builds on competences in muon reconstruction and muon spectrometer alignment and electron/photon identification.
Gluon tomography with exclusive vector meson production
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_service.php?id_unit=7
Thesis: Gluon tomography with exclusive vector meson production
The understanding of the origin of the mass, the spin and the structure of the nucleons (i.e. protons and neutrons) from their elementary constituents (quarks and gluons, collectively called partons) is among the unanswered questions in particle physics. The theoretical framework of the Generalized Parton Distributions (GPDs) encodes the 3-dimensional structure of a nucleon and its study will provide insights on the origin of the fundamental properties of protons and neutrons.
Experimentally, the cleanest method to study the internal structure of nucleons is to collide them with electrons at high energies. CEA/Irfu staff members are among the principal investigators of ongoing experiments at the Jefferson Lab (JLab) in USA, where a high current electron beam up to 11 GeV in energy collides with fixed targets of several types, and of the future experiments at the Electron Ion Collider (EIC), where electrons and protons will collide at energies in the center of mass up to 140 GeV. The high luminosities available at the JLab and at the future EIC allow the study of the properties of the nucleons with high statistical accuracy also via rare processes.
Contrary to the naive expectations, it has been shown that not the valence quarks, but rather the gluons carry the major contribution to the mass and the spin of the nucleons. Therefore, it is crucial to precisely characterize gluons distributions in order to fully understand the properties of the nucleons. In particular, the current knowledge of the GPDs of gluons is rather limited. GPDs are accessible through the study of exclusive processes where all the final state particles are detected, and specifically, gluon GPDs can be accessed via the study of the exclusive electo-production of vector mesons such as the rho, phi et omega mesons.
The goal of this thesis will be to analyze the data taken with the CLAS12 experiment at the Jefferson Lab focusing on measurements of exclusive meson production. Given the large size of the datasets, the student will have the opportunity to develop and apply machine learning algorithms to improve the reconstruction and the selection of event candidates. Extensive studies on simulated data will be necessary to fully understand the data, to train and optimize the candidate selection algorithms, to adapt ML models the real data and to tame possible systematic uncertainties. From the experience gained through the analysis of CLAS12 data, the candidate will also participate in the simulation studies for feasibility and optimization of the future detectors for the EIC for exclusive vector meson electro-production at high energies.
The thesis will be carried out within the Laboratory of Nucleon Structure of the Department of Nuclear Physics of CEA/Irfu. The laboratory is composed by both experimentalists and theorists: the frequent interactions make the work environment very enriching.
Knowledge of particle physics and computer science would help the candidate to quickly actively participate to the data analysis effort. Basics knowledge of particle detectors would be also an advantage to efficiently understand the experimental setup used for data collection.
The student will also have the opportunity to collaborate with several researchers both locally (like IJCLab in Orsay and CPHT at Ecole Polytechnique) and internationally. The student will be part of the CLAS collaboration and will also join the EIC user group that will also require trips to United States for data taking and workshops. The student will have the opportunity to present the result of these research topics to international conferences.
Contact: Francesco Bossù, CEA Saclay – IRFU/DPhN/LSN, (francesco.bossu@cea.fr)
The understanding of the origin of the mass, the spin and the structure of the nucleons (i.e. protons and neutrons) from their elementary constituents (quarks and gluons, collectively called partons) is among the unanswered questions in particle physics. The theoretical framework of the Generalized Parton Distributions (GPDs) encodes the 3-dimensional structure of a nucleon and its study will provide insights on the origin of the fundamental properties of protons and neutrons.
Experimentally, the cleanest method to study the internal structure of nucleons is to collide them with electrons at high energies. CEA/Irfu staff members are among the principal investigators of ongoing experiments at the Jefferson Lab (JLab) in USA, where a high current electron beam up to 11 GeV in energy collides with fixed targets of several types, and of the future experiments at the Electron Ion Collider (EIC), where electrons and protons will collide at energies in the center of mass up to 140 GeV. The high luminosities available at the JLab and at the future EIC allow the study of the properties of the nucleons with high statistical accuracy also via rare processes.
Contrary to the naive expectations, it has been shown that not the valence quarks, but rather the gluons carry the major contribution to the mass and the spin of the nucleons. Therefore, it is crucial to precisely characterize gluons distributions in order to fully understand the properties of the nucleons. In particular, the current knowledge of the GPDs of gluons is rather limited. GPDs are accessible through the study of exclusive processes where all the final state particles are detected, and specifically, gluon GPDs can be accessed via the study of the exclusive electo-production of vector mesons such as the rho, phi et omega mesons.
The goal of this thesis will be to analyze the data taken with the CLAS12 experiment at the Jefferson Lab focusing on measurements of exclusive meson production. Given the large size of the datasets, the student will have the opportunity to develop and apply machine learning algorithms to improve the reconstruction and the selection of event candidates. Extensive studies on simulated data will be necessary to fully understand the data, to train and optimize the candidate selection algorithms, to adapt ML models the real data and to tame possible systematic uncertainties. From the experience gained through the analysis of CLAS12 data, the candidate will also participate in the simulation studies for feasibility and optimization of the future detectors for the EIC for exclusive vector meson electro-production at high energies.
The thesis will be carried out within the Laboratory of Nucleon Structure of the Department of Nuclear Physics of CEA/Irfu. The laboratory is composed by both experimentalists and theorists: the frequent interactions make the work environment very enriching.
Knowledge of particle physics and computer science would help the candidate to quickly actively participate to the data analysis effort. Basics knowledge of particle detectors would be also an advantage to efficiently understand the experimental setup used for data collection.
The student will also have the opportunity to collaborate with several researchers both locally (like IJCLab in Orsay and CPHT at Ecole Polytechnique) and internationally. The student will be part of the CLAS collaboration and will also join the EIC user group that will also require trips to United States for data taking and workshops. The student will have the opportunity to present the result of these research topics to international conferences.
Contact: Francesco Bossù, CEA Saclay – IRFU/DPhN/LSN, (francesco.bossu@cea.fr)
LHC luminosity measurement with the ATLAS Liquid Argon Calorimeter and search for long lived massive particles
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Starting date : 01-10-2021
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Since the discovery of the Higgs boson efforts are focused on the search for new phenomena, beyond the Standard Model.
One of the important aspects of the comparison between experimental measurements and theory is the need to normalize as
precisely as possible experimental results to theory. This means in practice being able to measure as precisely as
possible the luminosity of the LHC. The goal is to reach a precision better than 1% within the next few years,
a factor two or three better than the precision that has been reached up to now.
After the LHC restart, foreseen in 2022, it is planned to increase the luminosity by a factor of about two. To make
the best out of this luminosity increase, the calorimeter trigger system is being significantly modified and upgraded.
The upgraded trigger system is based on real time analysis by FPGAs of the digitized detector signals.
An essential feature of the upgraded trigger system is its ability to measure the energy deposited in the calorimeter
bunch crossing by bunch crossing. Combined with the stability, excellent linearity and response uniformity of the ATLAS
Liquid Argon calorimeter, the upgraded trigger system offers the potential to measure the luminosity with excellent
linearity and stability performances. A very promising analysis technique would be to use a neural net, that
could be implemented in the core of the FPGA that processes the data.
An other feature of the upgraded trigger system is its ability to keep track of all the interactions taken place in the
detector over a much longer period of time than the main readout. The main readout system is able to keep in memory only
up to four or five consecutive interactions. The trigger system has the capability to keep track of each individual bunch
crossing over a period of time corresponding to several tens of consecutive bunch crossings.
This long term memory feature gives the possibility to compensate real time the effect of charge space accumulation,
which will be crucial for data taken after 2025, at very high luminosity. More importantly, this also opens up the
possibility to detect particles reaching the detector long (several tens or even hundreds of ns, to be compared to the
25 ns between two consecutive bunch crossings) after their production. Such particles are slow and very heavy, and can be
detected almost up to the kinematic limit of 7 TeV. This is significantly higher than the limits reachable by more
classic techniques. Such particles typically appear in many classes of supersymmetric models.
One of the important aspects of the comparison between experimental measurements and theory is the need to normalize as
precisely as possible experimental results to theory. This means in practice being able to measure as precisely as
possible the luminosity of the LHC. The goal is to reach a precision better than 1% within the next few years,
a factor two or three better than the precision that has been reached up to now.
After the LHC restart, foreseen in 2022, it is planned to increase the luminosity by a factor of about two. To make
the best out of this luminosity increase, the calorimeter trigger system is being significantly modified and upgraded.
The upgraded trigger system is based on real time analysis by FPGAs of the digitized detector signals.
An essential feature of the upgraded trigger system is its ability to measure the energy deposited in the calorimeter
bunch crossing by bunch crossing. Combined with the stability, excellent linearity and response uniformity of the ATLAS
Liquid Argon calorimeter, the upgraded trigger system offers the potential to measure the luminosity with excellent
linearity and stability performances. A very promising analysis technique would be to use a neural net, that
could be implemented in the core of the FPGA that processes the data.
An other feature of the upgraded trigger system is its ability to keep track of all the interactions taken place in the
detector over a much longer period of time than the main readout. The main readout system is able to keep in memory only
up to four or five consecutive interactions. The trigger system has the capability to keep track of each individual bunch
crossing over a period of time corresponding to several tens of consecutive bunch crossings.
This long term memory feature gives the possibility to compensate real time the effect of charge space accumulation,
which will be crucial for data taken after 2025, at very high luminosity. More importantly, this also opens up the
possibility to detect particles reaching the detector long (several tens or even hundreds of ns, to be compared to the
25 ns between two consecutive bunch crossings) after their production. Such particles are slow and very heavy, and can be
detected almost up to the kinematic limit of 7 TeV. This is significantly higher than the limits reachable by more
classic techniques. Such particles typically appear in many classes of supersymmetric models.
Charged particle tracking in heavy-ion collisions in LHCb and data analysis in fixed-target collisions at the LHC
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=500
Created in heavy-ion collisions at the LHC (CERN), the quark gluon plasma (QGP) is an extreme state of matter in which the constituents of nucleons are 'deconfined' sufficiently long in order to be studied.
Among the CERN LHC collaborations, LHCb studies the QGP both in collider mode, but also thanks to a fixed-target programme unique at the LHC.
The current performance of the tracking detectors is limited in the most violent collisions, but several upgrades are foreseen at the horizon of 2030.
The first goal of this thesis is the tracking development in order to assure optimal performances in future heavy-ion data takings. These studies will allow to define the performance parameters necessary to be achieved for the different subdetectors. Furthermore, alternative algorithms based on artificial intelligence will be explored in order to achieve the maximal detector performance. In parallel, an analysis component is proposed based on the fixed-target data. In particular, we propose to measure charm particle production. Unique in this kinematics and its energy range, these fixed-target collision measurements with the LHCb detector at the LHC will allow to establish better the role of charm quarks as observables sensitive of deconfinement.
Among the CERN LHC collaborations, LHCb studies the QGP both in collider mode, but also thanks to a fixed-target programme unique at the LHC.
The current performance of the tracking detectors is limited in the most violent collisions, but several upgrades are foreseen at the horizon of 2030.
The first goal of this thesis is the tracking development in order to assure optimal performances in future heavy-ion data takings. These studies will allow to define the performance parameters necessary to be achieved for the different subdetectors. Furthermore, alternative algorithms based on artificial intelligence will be explored in order to achieve the maximal detector performance. In parallel, an analysis component is proposed based on the fixed-target data. In particular, we propose to measure charm particle production. Unique in this kinematics and its energy range, these fixed-target collision measurements with the LHCb detector at the LHC will allow to establish better the role of charm quarks as observables sensitive of deconfinement.
Design, characterisation and exploitation of resistive MICROMEGAS for the near detector of DUNE
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Starting date : 01-10-2021
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Description and context
The Micro-pattern gaseous detectors (MPGD) community develops an ever stronger interest for resistive material. An international effort is ongoing to develop and exploit this bleeding edge technology. The main advantages lie with the stability against sparks and more recently with the improvement of the spatial resolution for the charge readout of time projection chambers (TPC). These breakthroughs will lead to the production of cutting-edge detectors. In particular for Micromegas detectors, invented at IRFU, this technology will be a crucial aspect for the physics program aiming at studying neutrino oscillations, a very promising field for the search for new physics.
The T2K and NOvA experiments currently study neutrino oscillations using a muon-neutrino beam produced at particle accelerators. The concept of DUNE is very similar to existing experiments. Neutrinos are produced in the interaction of a beam with a target and detected at two locations: the near detector site at ~ 540 m and the far detector site at ~ 1300 km. The synergy between the detectors on both sites allows the parameters governing neutrino oscillations to be measured and enables the reduction of the uncertainties coming from the flux or the neutrino interaction cross-sections. This will allow a very precise measurement of the CP violating phase and of the neutrino mass hierarchy. The measurement of CP violation in the leptonic sector would be a major discovery.
The beam monitoring for DUNE will be performed by the near detector SAND, using resistive Micromegas detectors in the TPCs used as inner tracker. The construction of the detector should be finished by 2026, making the future years crucial for the development of the required technologies. This physics program will require the stable and reliable operation of TPCs for over 10 years. Studies on the characterisation of the properties of the resistive materials or their ageing after long periods of operation time, in the presence of radiations or in extreme conditions (high currents, sudden increase and/or drops of temperature) will be necessary.
Description of the group, institute and supervision:
The Micromegas technology was invented at IRFU and the accelerator neutrino group at IRFU/DPhP has been at the heart of the developments on resistive Micromegas for the ILC. This participation continues with the current deployment of the technology for the near detector of T2K and the developments for DUNE/SAND. The accelerator neutrino group is constituted of 6 permanent scientists and 2 students involved in the resistive Micromegas activities. The physicists directly involved in SAND constitute a young and dynamic team which will benefit from the expertise of the group while developing its own on an experiment that should operate for many years to come.
The student will also benefit from the collaboration with the detector and technical services at IRFU/DEDIP, one of the international leaders in the development of micro-pattern gaseous detectors. Very advanced tools on detectors, DAQ, slow-control and electronics will therefore be available. Partnerships with other research institutes (e.g. CERN) and industrial exist and will be reinforce in the context of this work.
Proposed activities:
The student will focus on the understanding and the detailed characterization of the resistive foil used for the resistive Micromegas. The performances of these detectors, crucial for the sensitivity of the experiment, largely rely on the resistivity and the stability of these foils and dedicated studies are required before the production of the detectors by the end of 2025. A number of infrastructures are available at CEA (e.g. microscopy, ion beams) leading to the development of internal partnerships. CERN will also be a key partner in these studies, thanks to the upcoming acquisition of the installations necessary to the production of the resistive material in-house.
The student will also take part in the optimisation on test bench data and with simulations of the design of the resistive Micromegas detectors for the TPCs of SAND. Cosmic rays tests and beam tests will be necessary to characterise the detectors in real conditions. These tests will be performed at the beam lines of CERN and/or DESY and on the equipment at IRFU. The analysis of the data acquired during these tests, which will be done in collaboration with a post-doctoral researcher, will be one of the main activities and could result in a publication. The construction of the near detector of T2K is also supposed to be completed by Summer 2022. This will give the opportunity to the student, already during the internship, to take part in the testing of the resistive detectors in the context of the production of a final detector.
Another possible activity using simulations from the whole SAND detector will allow the theoretical systematic uncertainties to be reevaluated using new neutrino-nucleon interaction models, an important contribution to the sensitivity of SAND for the oscillation measurements with DUNE.
Education and skills required:
A Master's degree in particle physics with knowledge of the Standard Model or linked to the characterisation of thin foils is a requirement for this thesis. A strong interest for instrumental activities is expected and a motivation for neutrino physics is a very positive point. Experience of C++ and ROOT will also be very useful. Knowledge of the characterisation methods for thin foils and the interest in working at the interface with academic and industrial partners will be a major asset.
Acquired skills:
The student will have by the end of his/her PhD a good understanding of detectors and computing tools used in a particle physics collaboration thanks to his/her involvement in their developments. He/she will be able to promote his/her technical skills on detectors and on data analysis methods in other contexts.
Collaboration/Partnerships:
The student will work within the international collaboration DUNE strong of more than 1000 members. This will provide a very good experience in particle physics and an important visibility through the participation to physics schools, workshops and conferences where he/she will present his/her results. Collaborations with industrial partners will also be created and developed, partially under the impulse of the student.
The Micro-pattern gaseous detectors (MPGD) community develops an ever stronger interest for resistive material. An international effort is ongoing to develop and exploit this bleeding edge technology. The main advantages lie with the stability against sparks and more recently with the improvement of the spatial resolution for the charge readout of time projection chambers (TPC). These breakthroughs will lead to the production of cutting-edge detectors. In particular for Micromegas detectors, invented at IRFU, this technology will be a crucial aspect for the physics program aiming at studying neutrino oscillations, a very promising field for the search for new physics.
The T2K and NOvA experiments currently study neutrino oscillations using a muon-neutrino beam produced at particle accelerators. The concept of DUNE is very similar to existing experiments. Neutrinos are produced in the interaction of a beam with a target and detected at two locations: the near detector site at ~ 540 m and the far detector site at ~ 1300 km. The synergy between the detectors on both sites allows the parameters governing neutrino oscillations to be measured and enables the reduction of the uncertainties coming from the flux or the neutrino interaction cross-sections. This will allow a very precise measurement of the CP violating phase and of the neutrino mass hierarchy. The measurement of CP violation in the leptonic sector would be a major discovery.
The beam monitoring for DUNE will be performed by the near detector SAND, using resistive Micromegas detectors in the TPCs used as inner tracker. The construction of the detector should be finished by 2026, making the future years crucial for the development of the required technologies. This physics program will require the stable and reliable operation of TPCs for over 10 years. Studies on the characterisation of the properties of the resistive materials or their ageing after long periods of operation time, in the presence of radiations or in extreme conditions (high currents, sudden increase and/or drops of temperature) will be necessary.
Description of the group, institute and supervision:
The Micromegas technology was invented at IRFU and the accelerator neutrino group at IRFU/DPhP has been at the heart of the developments on resistive Micromegas for the ILC. This participation continues with the current deployment of the technology for the near detector of T2K and the developments for DUNE/SAND. The accelerator neutrino group is constituted of 6 permanent scientists and 2 students involved in the resistive Micromegas activities. The physicists directly involved in SAND constitute a young and dynamic team which will benefit from the expertise of the group while developing its own on an experiment that should operate for many years to come.
The student will also benefit from the collaboration with the detector and technical services at IRFU/DEDIP, one of the international leaders in the development of micro-pattern gaseous detectors. Very advanced tools on detectors, DAQ, slow-control and electronics will therefore be available. Partnerships with other research institutes (e.g. CERN) and industrial exist and will be reinforce in the context of this work.
Proposed activities:
The student will focus on the understanding and the detailed characterization of the resistive foil used for the resistive Micromegas. The performances of these detectors, crucial for the sensitivity of the experiment, largely rely on the resistivity and the stability of these foils and dedicated studies are required before the production of the detectors by the end of 2025. A number of infrastructures are available at CEA (e.g. microscopy, ion beams) leading to the development of internal partnerships. CERN will also be a key partner in these studies, thanks to the upcoming acquisition of the installations necessary to the production of the resistive material in-house.
The student will also take part in the optimisation on test bench data and with simulations of the design of the resistive Micromegas detectors for the TPCs of SAND. Cosmic rays tests and beam tests will be necessary to characterise the detectors in real conditions. These tests will be performed at the beam lines of CERN and/or DESY and on the equipment at IRFU. The analysis of the data acquired during these tests, which will be done in collaboration with a post-doctoral researcher, will be one of the main activities and could result in a publication. The construction of the near detector of T2K is also supposed to be completed by Summer 2022. This will give the opportunity to the student, already during the internship, to take part in the testing of the resistive detectors in the context of the production of a final detector.
Another possible activity using simulations from the whole SAND detector will allow the theoretical systematic uncertainties to be reevaluated using new neutrino-nucleon interaction models, an important contribution to the sensitivity of SAND for the oscillation measurements with DUNE.
Education and skills required:
A Master's degree in particle physics with knowledge of the Standard Model or linked to the characterisation of thin foils is a requirement for this thesis. A strong interest for instrumental activities is expected and a motivation for neutrino physics is a very positive point. Experience of C++ and ROOT will also be very useful. Knowledge of the characterisation methods for thin foils and the interest in working at the interface with academic and industrial partners will be a major asset.
Acquired skills:
The student will have by the end of his/her PhD a good understanding of detectors and computing tools used in a particle physics collaboration thanks to his/her involvement in their developments. He/she will be able to promote his/her technical skills on detectors and on data analysis methods in other contexts.
Collaboration/Partnerships:
The student will work within the international collaboration DUNE strong of more than 1000 members. This will provide a very good experience in particle physics and an important visibility through the participation to physics schools, workshops and conferences where he/she will present his/her results. Collaborations with industrial partners will also be created and developed, partially under the impulse of the student.
First seach for resonances with a mass below 70 GeV in the two-photons final state with the CMS detector
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Starting date : 01-10-2021
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The Standard Model (SM) of particle physics has been intensively tested experimentally over the past few decades and accurately fits the measurements. The latest major success of the SM is the discovery of the Higgs boson at the LHC in 2012. However, in the SM all is not clear. Many of the properties of the interactions and particles cannot be explained by the SM, such as the number of particle families or the differences in scale of their masses. Moreover, the SM has many free parameters to be determined experimentally, indicating that it is a theory that is only effective at low energy. More importantly, the SM can explain neither dark matter nor dark energy. While theorists are building new models to fill in these gaps, the experimentalists are trying to highlight physics beyond the SM, or ”new physics”, on the one hand by carrying out high-precision measurements to detect inconsistencies in the SM, and on the other by directly looking for new particles.
In 2012, both the ATLAS and CMS collaborations observed a new boson with a mass of approximately 125 GeV whose properties are at present compatible with those of the SM Higgs boson. The analyses of data in the diphoton final state (one of the two most sensitives modes) leading to this discovery probed an invariant mass range extending from 110 to 150 GeV. However, physics beyond the SM (BSM) can also provide a Higgs boson that is compatible with the observed 125 GeV boson. The extended parameter space of several BSM models, for example generalized models containing two Higgs doublets (2HDM) and the next-to-minimal supersymmetric model (NMSSM) gives rise to a rich and interesting phenomenology, including the presence of additional Higgs bosons, some of which could have masses below 125 GeV. Such models provide good motivation for extending searches for Higgs bosons to masses as far below mH = 110 GeV as possible.
Another mystery in the SM is the strong CP problem: why does the quantum chromodynamic (QCD) Lagrangian conserve CP symmetry, to within extraordinarily strict experimental limits, in absence of a correspondent fundamental symmetry? A possible way to make it natural, as introduced by Peccei and Quinn in 1977, is to add an extra global symmetry into the theory, the U(1) symmetry, that is spontaneously broken at some high energy fa. Such a symmetry leads in turn to the prediction of a new light pseudo-scalar particle: the axion, coupling to photons and gluons. A light axion (with a mass ma below the eV) could solve the strong CP problem. More generally, ”axion-like particles” (ALP) appear in any theory with a spontaneously broken global symmetry and can be searched for at particle colliders.
It is thus of primary importance to look for light resonances at the LHC and it is encouraged by many theorists. The X -> gamma gamma decay channel provides a clean final-state topology that allows the mass of a potential new resonance to be reconstructed with high precision. Present published direct searches at LHC in the diphoton decay channel cover a mass range down to about 65 to 70 GeV. Interesting limits could also be achieved in the lower mass range down to about 10 to 20 GeV. For example in ref [1], a conservative re-interpretation of inclusive diphoton cross section at LHC allows to put limits in this still unexplored region. Extending the mass range in the diphoton decay channel down to as lower masses as possible is what proposed in this thesis. Such a search is specially ambitious because of the difficulty to trigger on the signal. There is already a thesis about this on ATLAS, although the result is still not yet public.
This is the right moment to perform this search at LHC. Run 3 should start in the first half of 2022 and there should be about 133 fb-1 of new data available for the thesis. This very low mass analysis (below 70 GeV) has never been pursued in CMS. The triggers in run 2 were not optimised for this search, their pT thresholds were too high to have a good efficiency. In run 3, there is a possibility to adapt the trigger to gain in efficiency. Also, the run 2 data could still be used to set limits using the available boosted events. Since no limit at all is available at the moment in this mass region, even a mild one would be of interest. The thesis will be divided into 4 parts:
- During the 6 first months and before the start of run 3, the student will work on optimising a trigger for run 3 to gain in efficiency for this very low mass search. This means lowering the photons pT thresholds without taking too much bandwidth.
- Then, during the following year, the student will carry out and optimise the analysis of run 2 data.
- During the next 6 months, once the data in run 3 are recorded with a better suited trigger, the analysis of run 3 data will be carried out as well end eventually combined with the results from run 2.
- Finally, the last six months will be used to write the thesis.
The IRFU CMS group has a great expertise in photon energy measurement, as it has been involved in the ECAL construction and design and has a leading role in its calibration. There were recently several important responsibilities in the group relating to ECAL calibration (ECAL detector performance group conveners, electron/photon physics object group convener, ...). The IRFU CMS group did play an important role in H -> gamma gamma nalysis at 13 TeV. Two members of the saclay group were conveners of the H -> gamma gamma group during run 2. The group is also in close contact with the main authors of the current low mass analysis, based in Lyon (IP2I, IN2P3). The student will greatly benefit from group’s knowledge to lead these studies.
In 2012, both the ATLAS and CMS collaborations observed a new boson with a mass of approximately 125 GeV whose properties are at present compatible with those of the SM Higgs boson. The analyses of data in the diphoton final state (one of the two most sensitives modes) leading to this discovery probed an invariant mass range extending from 110 to 150 GeV. However, physics beyond the SM (BSM) can also provide a Higgs boson that is compatible with the observed 125 GeV boson. The extended parameter space of several BSM models, for example generalized models containing two Higgs doublets (2HDM) and the next-to-minimal supersymmetric model (NMSSM) gives rise to a rich and interesting phenomenology, including the presence of additional Higgs bosons, some of which could have masses below 125 GeV. Such models provide good motivation for extending searches for Higgs bosons to masses as far below mH = 110 GeV as possible.
Another mystery in the SM is the strong CP problem: why does the quantum chromodynamic (QCD) Lagrangian conserve CP symmetry, to within extraordinarily strict experimental limits, in absence of a correspondent fundamental symmetry? A possible way to make it natural, as introduced by Peccei and Quinn in 1977, is to add an extra global symmetry into the theory, the U(1) symmetry, that is spontaneously broken at some high energy fa. Such a symmetry leads in turn to the prediction of a new light pseudo-scalar particle: the axion, coupling to photons and gluons. A light axion (with a mass ma below the eV) could solve the strong CP problem. More generally, ”axion-like particles” (ALP) appear in any theory with a spontaneously broken global symmetry and can be searched for at particle colliders.
It is thus of primary importance to look for light resonances at the LHC and it is encouraged by many theorists. The X -> gamma gamma decay channel provides a clean final-state topology that allows the mass of a potential new resonance to be reconstructed with high precision. Present published direct searches at LHC in the diphoton decay channel cover a mass range down to about 65 to 70 GeV. Interesting limits could also be achieved in the lower mass range down to about 10 to 20 GeV. For example in ref [1], a conservative re-interpretation of inclusive diphoton cross section at LHC allows to put limits in this still unexplored region. Extending the mass range in the diphoton decay channel down to as lower masses as possible is what proposed in this thesis. Such a search is specially ambitious because of the difficulty to trigger on the signal. There is already a thesis about this on ATLAS, although the result is still not yet public.
This is the right moment to perform this search at LHC. Run 3 should start in the first half of 2022 and there should be about 133 fb-1 of new data available for the thesis. This very low mass analysis (below 70 GeV) has never been pursued in CMS. The triggers in run 2 were not optimised for this search, their pT thresholds were too high to have a good efficiency. In run 3, there is a possibility to adapt the trigger to gain in efficiency. Also, the run 2 data could still be used to set limits using the available boosted events. Since no limit at all is available at the moment in this mass region, even a mild one would be of interest. The thesis will be divided into 4 parts:
- During the 6 first months and before the start of run 3, the student will work on optimising a trigger for run 3 to gain in efficiency for this very low mass search. This means lowering the photons pT thresholds without taking too much bandwidth.
- Then, during the following year, the student will carry out and optimise the analysis of run 2 data.
- During the next 6 months, once the data in run 3 are recorded with a better suited trigger, the analysis of run 3 data will be carried out as well end eventually combined with the results from run 2.
- Finally, the last six months will be used to write the thesis.
The IRFU CMS group has a great expertise in photon energy measurement, as it has been involved in the ECAL construction and design and has a leading role in its calibration. There were recently several important responsibilities in the group relating to ECAL calibration (ECAL detector performance group conveners, electron/photon physics object group convener, ...). The IRFU CMS group did play an important role in H -> gamma gamma nalysis at 13 TeV. Two members of the saclay group were conveners of the H -> gamma gamma group during run 2. The group is also in close contact with the main authors of the current low mass analysis, based in Lyon (IP2I, IN2P3). The student will greatly benefit from group’s knowledge to lead these studies.
Towards a high spatial resolution pixel detector for particle identification: new detectors contribution to physics
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Starting date : 01-09-2021
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More : https://doi.org/10.1109/TED.2017.2670681
Future experiments on linear colliders (e+e-) with low hadronic background require improvements in the spatial resolution of pixel vertex detectors to the micron range, in order to determine precisely the primary and secondary vertices for particles with a high transverse momentum. This kind of detector is set closest to the interaction point. This will provide the opportunity to make precision lifetime measurements of short-lived charged particles. We need to develop pixels arrays with a pixel dimension below the micron squared. The proposed technologies (DOTPIX: Quantum Dot Pixels) should give a significant advance in particle tracking and vertexing. Although the principle of these new devices has been already been studied in IRFU (see reference), this doctoral work should focus on the study of real devices which should then be fabricated using nanotechnologies in collaboration with other Institutes. This should require the use of simulation codes and the fabrication of test structures. Applications outside basics physics are X ray imaging and optimum resolution sensors for visible light holographic cameras.
Coherent Elastic Neutrino-Nucleus scattering and search for new physics with the NUCLEUS experiment
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Starting date : 01-10-2021
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Laboratory link : http://irfu-i.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=424
More : http://irfu-i.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=4248
This PhD topic is about the NUCLEUS experiment, which aims at precisely measuring coherent elastic neutrino-nucleus scattering (CEvNS) at the Chooz nuclear power plant (France). Although at ~MeV energies, CEvNS is the predominant interaction process of neutrinos with matter, it has remained unobserved for a very long time because of the difficulty to measure the very low energy nuclear recoils it induces. It was only 40 years after its first prediction that this process was observed in 2017 with neutrinos of a few tens of MeV at the Oak Ridge laboratory (Tennessee). The first detection of CEvNS at a nuclear reactor remains to be achieved, especially because the corresponding nuclear recoils lie in an energy regime (~100 eV) which is difficult to measure with conventional detection technologies, and also because of the unfavorable background conditions nuclear power plant environments generally offer. The NUCLEUS collaboration is therefore working on the design of an innovative detection system using two cryogenic calorimeter arrays capable of reaching ~10 eV energy thresholds, and surrounded by a twofold system of instrumented cryogenic vetoes. This set of cryogenic detectors will be protected by an external passive shielding and by a muon veto to improve the identification and discrimination of backgrounds. With this system, NUCLEUS aims at a precise measurement of CEvNS in order to push the study of the fundamental properties of the neutrino as well as the search for beyond standard model physics towards the low energy frontier. Interestingly, CEvNS also exhibits a cross-section 10 to 1000 times larger than the usual ~MeV neutrino detection channels (inverse beta decay reaction, neutrino-electron scattering process), making it possible to miniaturize future long-range neutrino detection setups. The first phase of the NUCLEUS experiment will for instance deploy an array of cryogenic calorimeters made of sapphire (Al2O3) and calcium tungstate (CaWO4) crystals, totaling 10 g of detector.
In addition to the characterization and preparation of the experimental site at Chooz, our team at Irfu is taking a leading role in the project through several hardware and software developments. In particular, the DPhP is strongly involved in the realization of one of the instrumented cryogenic shielding of the experiment, here called the cryogenic outer veto. This detector consists of an arrangement of high-purity Germanium crystals, erected around the two cryogenic calorimeter arrays, and operated in ionization mode. This detection system will play a central role in the identification and discrimination of external backgrounds, such as ambient gamma radioactivity or atmospheric muons resulting from the interaction of primary cosmic rays in the atmosphere. The exploitation of the data delivered by this detector is then a natural entry in the global analysis effort to extract a first CEvNS signal at a reactor, with first background data collected in 2021/2022 during the blank assembly phase at the Technical University of Munich, and with data collected during the first physics run planned in 2023 at Chooz.
The work proposed in this PhD thesis is focused on the external cryogenic veto of the experiment, with the ultimate goal of achieving a comprehensive understanding of the backgrounds in the CEvNS region of interest, between 0.01 and 1 keV. The priority at the beginning will be given to the realization and commissioning of the external cryogenic veto system during the blank assembly phase in Munich. This work includes the assembly of the different detector elements (crystals, support mechanics, readout electronics, etc.) in the cryostat of the experiment, and includes all the necessary tests to validate and quantify the performances of this detector. In a second step, the student will ramp up in the collaboration analysis effort by contributing to the development of analysis and simulation tools. These tools will be used to interpret the background and detector calibration data acquired during the blank assembly phase and during the first physics run. He (she) will focus on the study of a specific source of external background, and quantify its impact on the physics potential of the experiment. This work will require a good understanding of the processes governing radiation interactions in matter and of the solid-state physics driving the behavior of cryogenic detectors (e.g. phonon propagation). Finally, the student will use the first data from the physics run at Chooz to conduct a search for new physics beyond the standard model (measurement of the weak mixing angle at low energies, search for new neutrino couplings, constraints on the electromagnetic properties of the neutrino, etc.). This work will require the implementation of advanced statistical methods for interpreting the data, in order on the one hand to understand the impact of the various sources of uncertainty on the constraints obtained, and on the other hand to guarantee the reliability of the results.
In addition to the characterization and preparation of the experimental site at Chooz, our team at Irfu is taking a leading role in the project through several hardware and software developments. In particular, the DPhP is strongly involved in the realization of one of the instrumented cryogenic shielding of the experiment, here called the cryogenic outer veto. This detector consists of an arrangement of high-purity Germanium crystals, erected around the two cryogenic calorimeter arrays, and operated in ionization mode. This detection system will play a central role in the identification and discrimination of external backgrounds, such as ambient gamma radioactivity or atmospheric muons resulting from the interaction of primary cosmic rays in the atmosphere. The exploitation of the data delivered by this detector is then a natural entry in the global analysis effort to extract a first CEvNS signal at a reactor, with first background data collected in 2021/2022 during the blank assembly phase at the Technical University of Munich, and with data collected during the first physics run planned in 2023 at Chooz.
The work proposed in this PhD thesis is focused on the external cryogenic veto of the experiment, with the ultimate goal of achieving a comprehensive understanding of the backgrounds in the CEvNS region of interest, between 0.01 and 1 keV. The priority at the beginning will be given to the realization and commissioning of the external cryogenic veto system during the blank assembly phase in Munich. This work includes the assembly of the different detector elements (crystals, support mechanics, readout electronics, etc.) in the cryostat of the experiment, and includes all the necessary tests to validate and quantify the performances of this detector. In a second step, the student will ramp up in the collaboration analysis effort by contributing to the development of analysis and simulation tools. These tools will be used to interpret the background and detector calibration data acquired during the blank assembly phase and during the first physics run. He (she) will focus on the study of a specific source of external background, and quantify its impact on the physics potential of the experiment. This work will require a good understanding of the processes governing radiation interactions in matter and of the solid-state physics driving the behavior of cryogenic detectors (e.g. phonon propagation). Finally, the student will use the first data from the physics run at Chooz to conduct a search for new physics beyond the standard model (measurement of the weak mixing angle at low energies, search for new neutrino couplings, constraints on the electromagnetic properties of the neutrino, etc.). This work will require the implementation of advanced statistical methods for interpreting the data, in order on the one hand to understand the impact of the various sources of uncertainty on the constraints obtained, and on the other hand to guarantee the reliability of the results.
Deep learning to discover rare complex signals with the Atlas experiment at the LHC
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Starting date : 01-10-2021
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This PhD proposes to apply artificial intelligence algorithms to big data in two innovative ways by exploiting the large proton-proton collision dataset collected by the ATLAS experiment at the Large Hadron Collider (LHC). The challenge is to extract processes that are both rare and complex from the huge amount of LHC data. Cutting edge deep learning techniques will be explored first to reconstruct complex final states with underconstrained kinematics. This would allow reconstructing final state particle energies and momenta knowing some conservation laws. Second deep learning will be implemented to extract rare signals. These new developments will be applied to two very rare and complex processes (ttH and 4-top). These two processes combined will allow testing the true nature of the coupling between the cornerstone of the Standard Model, the Higgs boson, and the heaviest elementary particle, the top quark, and could reveal new sources of asymmetry between matter and anti-matter. First unsupervised training will be tested for the first time for final state reconstruction. Observables based on the fully or partially reconstructed final state particles should then improve the ability to extract rare signals using for instance Graph Neural Network classifiers newly in high energy physics.
Exploring these new strategies for event reconstruction and classification will pave the way to understanding how the increased amount of data expected in the next phase of the LHC can be exploited in an optimal way.
Exploring these new strategies for event reconstruction and classification will pave the way to understanding how the increased amount of data expected in the next phase of the LHC can be exploited in an optimal way.
3D imaging of a nuclear reactor during its decommissioning using muon tomography
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast.php?t=fait_marquant&id_ast=4827
The final goal of this PhD thesis is to obtain the very first 3D image of a nuclear reactor with a non-invasive method, namely the muography. This penetrating imaging technique has shown a rapid development during the last years, with major technological improvements including several innovative contributions from the CEA. Muon telescopes of unprecedented resolution thus unveiled the 2D structures of very large objects like Khufu’s Pyramid or a nuclear reactor. Recently, an algorithm was developed to combine these 2D images in a 3D tomography, despite the small number of available projections and the huge size of the corresponding matrix system. This PhD will then be dedicated to the use of this algorithm to ongoing muography measurements on a nuclear reactor in decommissioning phase. The PhD student will actively participate to the data taking, data analysis and to the corresponding simulations. He/She will first apply the algorithm to smaller objects, in particular nuclear waste containers in various environments, in order to understand and optimize its performance. These intermediate steps, beyond their own interest, will help to better tune the algorithm parameters but also to determine the future measurements (positions, orientations, acquisition times, etc.). The overall goal of this work is thus the development of a 3D, generic, innovative imaging tool in the field of decontamination & decommissioning, with certainly many more applications in the societal and academic domains.
ARTIFICIAL INTELLIGENCE TO SIMULATE BIG DATA AND SEARCH FOR THE HIGGS BOSON DECAY TO A PAIR OF MUONS WITH THE ATLAS EXPERIMENT AT THE LARGE HADRON COLLIDER
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Starting date : 01-09-2021
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New artificial intelligence techniques are attracting growing interest in handling the massive volume of data collected by particle physics experiments, particularly at the LHC collider. This thesis proposes to study these new techniques for the simulation of the background noise of rare events originating from the decay into two muons of the Higgs boson as well as to set up a new artificial intelligence method to extract these rare events from the gigantic dimuon background noise.
In 2012, the Higgs boson, a fundamental part of the Standard Model of particle physics, was discovered at the LHC. The demonstration of its decay in dimuon is now at the heart of the LHC program to measure the coupling of the Higgs boson to 2nd generation particles.
Simulating the dimuon background with sufficient statistics is the first challenge of this analysis. The thesis proposes to test, for the first time, the use of very promising artificial intelligence models as a simulation method using "Generative Adversarial Networks (GANs)" with an architecture of two competing networks. In addition, the thesis also foresees a complete redesign of the analysis in order to implement new data processing methods (Deep Neural Networks) to optimize the extraction of the weak signal.
In 2012, the Higgs boson, a fundamental part of the Standard Model of particle physics, was discovered at the LHC. The demonstration of its decay in dimuon is now at the heart of the LHC program to measure the coupling of the Higgs boson to 2nd generation particles.
Simulating the dimuon background with sufficient statistics is the first challenge of this analysis. The thesis proposes to test, for the first time, the use of very promising artificial intelligence models as a simulation method using "Generative Adversarial Networks (GANs)" with an architecture of two competing networks. In addition, the thesis also foresees a complete redesign of the analysis in order to implement new data processing methods (Deep Neural Networks) to optimize the extraction of the weak signal.
Axion searches with the International Axion Observatory with ultra low background Micromegas detectors
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Starting date : 01-10-2021
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Personal web page : http://irfu.cea.fr/Pisp/esther.ferrer-ribas/
Laboratory link : http://irfu.cea.fr/dedip/index.php
More : https://iaxo.web.cern.ch/content/home-international-axion-observatory
Axions were introduced as the most promising solution in explaining the absence of Charge-Parity symmetry violation in the strong interaction. These neutral, very light particles, interact so weakly with ordinary matter that they could contribute to the Dark Matter. Axion search techniques rely on their interaction with photons. Helioscopes search for axions produced in the solar core by the conversion of plasma photons into axions giving rise to a solar axion flux at the Earth surface, with energy spectrum at the region 1-10 keV.
The International Axion Observatory (IAXO) will achieve a signal-to-background ratio of about 4-5 orders of magnitude better than most sensitive experiments today. BabyIAXO, an intermediate experimental stage of IAXO, will be hosted at DESY (Germany). BabyIAXO is conceived to test all IAXO subsystems (magnet, optics and detectors) at a relevant scale for the final system and thus serve as prototype for IAXO, but at the same time as a fully-fledged helioscope with relevant physics reach in itself, and with potential for discovery. IAXO and BabyIAXO will be equipped with X-ray optics coupled to low background X-ray detectors. The required levels of background are extremely challenging, a factor 10 better than current levels.
The PhD will work on the X-ray detector development in particular of the new generation of Micromegas detectors. The development will be focused on the optimization of the background level by a multi-approach strategy coming from ground measurements, screening campaigns of components of the detector, underground measurements, background models, in-situ background measurements as well as refinement of rejection algorithms. Physics analysis of BabyIAXO data is expected in the last year of the PhD.
The International Axion Observatory (IAXO) will achieve a signal-to-background ratio of about 4-5 orders of magnitude better than most sensitive experiments today. BabyIAXO, an intermediate experimental stage of IAXO, will be hosted at DESY (Germany). BabyIAXO is conceived to test all IAXO subsystems (magnet, optics and detectors) at a relevant scale for the final system and thus serve as prototype for IAXO, but at the same time as a fully-fledged helioscope with relevant physics reach in itself, and with potential for discovery. IAXO and BabyIAXO will be equipped with X-ray optics coupled to low background X-ray detectors. The required levels of background are extremely challenging, a factor 10 better than current levels.
The PhD will work on the X-ray detector development in particular of the new generation of Micromegas detectors. The development will be focused on the optimization of the background level by a multi-approach strategy coming from ground measurements, screening campaigns of components of the detector, underground measurements, background models, in-situ background measurements as well as refinement of rejection algorithms. Physics analysis of BabyIAXO data is expected in the last year of the PhD.
MEASUREMENT OF THE W-BOSON MASS WITH THE ATLAS DETECTOR AT THE LHC
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Starting date : 01-09-2021
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The goal of the thesis is a measurement of a fundamental parameter in the Standard Model of particle physics, the W boson mass, with the ATLAS detector at the LHC, using leptonic W boson decays. The analysis will be based on dedicated low-pile-up data samples, which have limited integrated luminosity but optimal experimental resolution in the reconstruction of missing transverse energy, which is a requirement in the analysis of final states with neutrinos.
The candidate will participate in the installation and the commissioning of the New Small Wheel, an upgraded muon detector for the ATLAS endcaps. IRFU has played a leading role in its construction and will get strongly involved in its scientific exploitation. In addition, the candidate will calibrate the muon momentum with sufficient precision for the measurement. The second phase of the project consists in improving the QCD aspects of the modelling of W-boson production and decay, and optimizing the analysis to minimize the resulting measurement uncertainty. After completion, the measurement will be interpreted in terms of compatibility with the Standard Model or as a hint of New Physics.
The candidate will participate in the installation and the commissioning of the New Small Wheel, an upgraded muon detector for the ATLAS endcaps. IRFU has played a leading role in its construction and will get strongly involved in its scientific exploitation. In addition, the candidate will calibrate the muon momentum with sufficient precision for the measurement. The second phase of the project consists in improving the QCD aspects of the modelling of W-boson production and decay, and optimizing the analysis to minimize the resulting measurement uncertainty. After completion, the measurement will be interpreted in terms of compatibility with the Standard Model or as a hint of New Physics.
Measuring four and three top-quark production in the multilepton channel at the ATLAS experiment
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Starting date : 01-10-2021
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The proposed PhD is aiming at observing for the first time the production of four top quark (tttt) at the LHC using the multilepton signature in data collected with the ATLAS experiment. The production of four top quarks is one of the most spectacular final states which became accessible at the LHC. While expected to be small in the Standard Model, the tttt cross section is predicted to be strongly enhanced in many new physics scenarios. The tttt process is also sensitive to the detailed properties of the Yukawa-like interaction between the top quark and the Higgs boson. Probing further this class of events over the next years will therefore be crucial to understand better the true nature of the Higgs-top-quark interaction and potentially to pinpoint subtle deviations from the Standard Model.
Several innovative ways will be pursued to reach the observation of this tttt process. First a better separation between the signal and the different background processes will be studied by designing various multivariate discriminants and by a better understanding of the modeling of the ttW process. Another path towards observation will be to study the possibility to reconstruct the different top quarks in the final state, which is particularly challenging in this channel.
Achieving a measurement of the tttt production will allow to probe a key property of the top-Higgs interaction, i.e. the CP nature of the top-Higgs coupling. Ultimately, the tttt process should also be measured separately from the production of three top quarks, which is currently totally unexplored experimentally.
Several innovative ways will be pursued to reach the observation of this tttt process. First a better separation between the signal and the different background processes will be studied by designing various multivariate discriminants and by a better understanding of the modeling of the ttW process. Another path towards observation will be to study the possibility to reconstruct the different top quarks in the final state, which is particularly challenging in this channel.
Achieving a measurement of the tttt production will allow to probe a key property of the top-Higgs interaction, i.e. the CP nature of the top-Higgs coupling. Ultimately, the tttt process should also be measured separately from the production of three top quarks, which is currently totally unexplored experimentally.
Discovering the nature of the Higgs-top coupling using deep learning with the Atlas experiment at the LHC
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Starting date : 01-09-2021
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This PhD proposes to shed light on the nature of the coupling between the Higgs boson and the top quark using artificial intelligence algorithms by exploiting the large proton-proton collision dataset collected by the ATLAS experiment at the Large Hadron Collider (LHC). The challenge is to extract processes that are both rare and complex from the huge amount of LHC data. The two rare processes that will be studied are the production of a Higgs boson with a pair of top quarks and the production of four top quarks. These two processes combined can allow to test the nature of the coupling between the cornerstone of the Standard Model, the Higgs boson, and the heaviest elementary particle, the top quark, and could reveal new sources of asymmetry between matter and antimatter. Discovering such new sources is one of the crucial questions in physics today in order to explain why our Universe is mainly composed of matter. Two innovative aspects will be pursued to study these processes both based on cutting edge deep learning techniques. First unsupervised training will be tested for the first time for complex final state reconstruction with underconstrained kinematics due to the presence of neutrinos. Then observables based on the fully or partially reconstructed final state particles will be used to improve the ability to extract these rare signals and then to enlighten the nature of the Higgs-top coupling. Exploring these new strategies for event reconstruction and classification will pave the way to understanding how the increased amount of data expected in the next ‘high luminosity’ phase of the LHC can be exploited in an optimal way.
A simultaneous determination of parton-distribution and fragmentation functions using artificial neural networks
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Starting date : 01-10-2021
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Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=4189
Quantum chromodynamics (QCD) is the most fundamental expression of the nuclear interaction known. It is a theory strongly coupled to energies of the order of the mass of the proton, or more generally of light nuclei. In general, the buildings made of quarks and gluons, called hadrons, are specified by two types of distributions: the parton distribution functions (PDFs) and the fragmentation functions (FFs). In a collision involving protons as at the LHC, the PDFs characterise the initial state of the collision while the FFs describe the production of hadrons in the final state. A better knowledge of these objects is therefore absolutely essential to allow for an optimal exploitation of experimental data, in nuclear physics but also in Standard Model physics and beyond. Moreover, these distributions provide valuable information on the transition between observed (hadrons) and fundamental (quarks and gluons, confined in hadrons) degrees of freedom.
Until now, most determinations of PDFs and FFs have been independent and based on parameterisations of these distributions fitted to a large amount of diverse experimental data. The goal of this thesis project is to simultaneously determine PDFs and FFs by describing them with artificial neural networks (ANNs). The simultaneous analysis is still unprecedented at the international level and will achieve an optimal exploitation of the experimental data. Finally, the use of ANNs will reduce the parametric bias. Previous works of the thesis host team have already shown the major interest of ANNs for the determination of PDFs. By developing the same technologies, the extension to FFs will also be a world first. These two elements will allow for a more accurate determination of PDFs and FFs.
Until now, most determinations of PDFs and FFs have been independent and based on parameterisations of these distributions fitted to a large amount of diverse experimental data. The goal of this thesis project is to simultaneously determine PDFs and FFs by describing them with artificial neural networks (ANNs). The simultaneous analysis is still unprecedented at the international level and will achieve an optimal exploitation of the experimental data. Finally, the use of ANNs will reduce the parametric bias. Previous works of the thesis host team have already shown the major interest of ANNs for the determination of PDFs. By developing the same technologies, the extension to FFs will also be a world first. These two elements will allow for a more accurate determination of PDFs and FFs.
