PhD subjects

56 sujets IRFU

Dernière mise à jour : 23-06-2018


• Accelerators physics

• Astroparticles

• Astrophysics

• Electromagnetism - Electrical engineering

• Mathematics - Numerical analysis - Simulation

• Medical imaging

• Nuclear Physics

• Nuclear physics

• Particle physics

• Solid state physics, surfaces and interfaces

 

JWST: from data analysis software and techniques to the quest for hidden mergers in high redshift galaxies

SL-DRF-18-0255

Location :

Service d'Astrophysique (DAP)

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

Emanuele DADDI

Starting date : 01-10-2018

Contact :

Emanuele DADDI

CEA - DRF/IRFU/SAp

Thesis supervisor :

Emanuele DADDI

CEA - DRF/IRFU/SAp

WST will be launched early in 2019, with an important participation from ESA, CNES and CEA for the mid-infrared instrument MIRI. JWST capabilities are revolutionary, compared to the existing state of the art, in terms of resolution and sensitivity over the 1- 30?m wavelength range, where stars and (warm) dust emit their light from galaxies at high redshift. For the first time JWST will provide spatially resolved photometry up to the mid-IR (at least 10?m, with NIRCAM and MIRI) with sub-arcsec resolution. The competitive exploitation of the data for scientific endeavors will require the mastering of the data, deeply understanding the reduction, treatment and developing tools to foster the analysis. I propose a PhD thesis in Saclay as a collaborative effort between experts from 'MICE, the Centre of Expertise for MIRI', developed at CEA/Irfu/DAp, and with researchers in galaxy formation and evolution. The student will be responsible for developing new high level software for the analysis of resolved imaging data from MIRI and NIRCAM, modeling and understand the resolution, 'pixelization' and PSF convolution effects. This will include high-level software to create spatially resolved maps of physical parameters (stellar mass, dust attenuation, stellar age, star formation rate) and pixel-by-pixel spectral energy distributions. The student will work on testing and improving the existing MIRI simulator, adapting it to the case of resolved observations of distant galaxies. The results of the efforts will be shared with several of the CEA Saclay groups in the spirit of fostering our expertise and efficiency in the early use of the groundbreaking JWST data. This work will be based on data from our recently approved Early Release Science (ERS) project observing with a suite of JWST instruments (NIRCAM, NIRSPEC, and MIRI) on well-studied cosmological fields. This ERS project is lead by S. Finkelstein at the University of Texas and includes E. Daddi and D. Elbaz from CEA-Saclay among the international teams of proposers. These observations will be among the first delivered by JWST, in parallel with those from GTO teams.

The student will ultimately use the Early Release Science data on cosmological fields to search for ongoing hidden merger events and AGN components resolved inside galaxies, by distinguishing them from the whole galaxy (e.g., nuclear events, or similar). These are lower luminosities and therefore much more frequent events, which affect only a subset of the galaxy, while the rest behaves as a normal disk, similar to M82 that could be a local proto-type of this situation. This research is based on recent discoveries from our team at the peak of galaxy formation z=1-4, including ALMA high resolution observations of distant star forming galaxies showing compact dust embedded cores (Cibinel, Daddi, Bournaud et al 2017), near-IR rest frame line spectroscopy of distant starbursts showing optically thick cores with growing AGNs (Calabro, Daddi et al in preparation), and other ongoing works. Eventually this research will lead to the first realistic estimate of the impact of mergers on star formation in the distant Universe, a widely discussed and hot topic. Also, we could shed new lights on the issues of black hole growth duty cycle and the role of feedback in terminating star formation at high redshifts.

Spin effects at high dimuon mass spectrum in the CMS experiment at LHC

SL-DRF-18-0305

Location :

Service de Physique des Particules (DPHP)

Groupe CMS

Saclay

Contact :

elizabeth Locci

Starting date : 01-10-2018

Contact :

elizabeth Locci

CEA - DSM/IRFU/SPP

0041227673965

Thesis supervisor :

elizabeth Locci

CEA - DSM/IRFU/SPP

0041227673965

The Standard Model Higgs boson has been searched for in the µ+µ- decay channel in pp collisions at 7 and 8

TeV (center-of-mass energy) . At the Higgs boson mass of 125 GeV/c2 the observed 95% C.L. upper limit on

the production rate is found to be 7.4 times the standard model prediction rate.

At 13 TeV the statistics is expected to be multiplied by a factor 8 to 10. Not only the Higgs branching ratio will

be measured more precisely but it will be possible to identify spin discriminating variables for the Higgs boson

(spin 0) with respect to the Z boson (spin 1) that could be used in the search for additional spin 0 or spin 2

resonances at higher mass.

Studies of the Higgs boson selfcoupling with the HH -> bbgg reconstruction in the CMS experiment at the LHC

SL-DRF-18-0304

Location :

Service de Physique des Particules (DPHP)

Groupe CMS

Saclay

Contact :

Serguei GANJOUR

Starting date : 01-10-2018

Contact :

Serguei GANJOUR

CEA - DSM/IRFU/SPP/CMS

Thesis supervisor :

Serguei GANJOUR

CEA - DSM/IRFU/SPP/CMS

The limits for the observation of the production of resonant and non resonant Higgs pair reconstructed into two b-jets and two photons(HH->bbgg) have been published(Phys. Rev. D 94, 052012 (2016)) by CMS for the LHC RUN-1 data, at 8 TeV. The HH->bbgg reconstruction using the RUN-2 data at 13 TeV with the CMS detector will allow the study of the Higgs self coupling and its coupling to the top quark.

Reaching non-linear scales in theories of Dark Energy and Modified Gravity

SL-DRF-18-0436

Location :

Service d'Astrophysique (DAP)

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Valeria Pettorino

Starting date : 01-04-2018

Contact :

Valeria Pettorino

CEA - DRF/IRFU/SAp/LCS

Thesis supervisor :

Valeria Pettorino

CEA - DRF/IRFU/SAp/LCS

Personal web page : http://www.cosmostat.org/people/valeria-pettorino

Laboratory link : http://www.cosmostat.org/

The nature of Dark Energy (DE), responsible for the accelerated expansion of the Universe, is the

main puzzle of nowadays cosmology. Whether it is a constant or a fluid or a hint that gravity and

Einstein’s theory of General Relativity have to be modified (Modified Gravity, MG) at very large

scales, remains unknown. To solve this fundamental problem, the community has run many

observational projects and a large amount of data will become available in the next few years

from a variety of probes.

The PhD hired within this project will be at the interface between theory and observations to get

the best scientific return out of the big investment done, in particular in Europe.

Objectives include: i) developing a module for MG that allows to include non-linear scales, so far

mainly excluded from the analysis ii) comparing new available data to general theoretical

approaches to understand the nature of DE and MG iii) combining different probes to detect,

constrain or exclude classes of models.

Ultimately, this will allow confirming or disproving the standard theory of Einstein, leading to

new insights in fundamental physics.

Light Ion Source Optimisation for High Intensity production

SL-DRF-18-0418

Research field : Accelerators physics
Location :

Service des Accélérateurs, de Cryogénie et de Magnétisme (DACM)

Laboratoire d'Etudes et de Développements pour les Accélérateurs (LEDA)

Saclay

Contact :

Olivier TUSKE

Starting date :

Contact :

Olivier TUSKE

CEA - DRF/IRFU/SACM/LEDA

+33 1 69 08 68 20

Thesis supervisor :

Olivier TUSKE

CEA - DRF/IRFU/SACM/LEDA

+33 1 69 08 68 20

Since more than 20 years, CEA Saclay developed and built high intensity ion sources for accelerators, mainly heated by the electronic cyclotronic resonnant mechanism (ECR). The experience of the CEA is well recognize worldwide, our group was chosen to built ion sources for different facilities: IFMIF/LIPAc (Japan), SPIRAL2 facility (France) and FAIR in Germany.

High performances, in particular the high reliability of our ions sources made them essential for futur high intensity neutron source for fusion reactor material research, or experiences in neutron diffraction or cancer cure with the boron neutron capture therapy (BNCT).

The aim of this thesis is to provide us to a better understanding of the physical phenomena inside the ion sources, as the microwave-plasma interaction/coupling, or the plasma confinement. The primary goal is to optimize beam quality for ions sources, in term of stability in time, in homogeneity and purity but also to increase the extracted current far beyond actual performances. Compact ion sources with a better efficiency are also expected.

This ambitious program could be only validated with various experimental measurements at Saclay on a plasma reactor or on an extracted intense light ion beam with dedicated diagnostics.

Mastering high intensity beam production is the key of the future. Those innovative ion sources will play a large part in maintaining CEA leadership in the field of light ion sources and also in particles accelerators.

Innovative bolometers for neutrino physics

SL-DRF-18-0329

Research field : Astroparticles
Location :

Service de Physique des Particules (DPHP)

Groupe Edelweiss

Saclay

Contact :

Claudia Nones

Starting date : 01-10-2018

Contact :

Claudia Nones

CEA - DRF/IRFU/SPP/Edelweiss

0169083520

Thesis supervisor :

Claudia Nones

CEA - DRF/IRFU/SPP/Edelweiss

0169083520

Personal web page : http://irfu.cea.fr/Pisp/claudia.nones/

Laboratory link : http://irfu.cea.fr/Spp/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3900

High-energy multi-messenger astrophysics with H.E.S.S./CTA and HAWC

SL-DRF-18-0256

Research field : Astroparticles
Location :

Service de Physique des Particules (DPHP)

Groupe HESS 2

Saclay

Contact :

Fabian Schussler

Starting date : 01-09-2017

Contact :

Fabian Schussler

CEA - DRF/IRFU/SPP/HESS 2

+33169083020

Thesis supervisor :

Fabian Schussler

CEA - DRF/IRFU/SPP/HESS 2

+33169083020

Personal web page : http://irfu.cea.fr/Pisp/fabian.schussler/index.html

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 system will be H.E.S.S., the world’s most sensitive gamma-ray observatory, and HAWC, the world’s largest water Cherenkov detector recording the highest-energy gamma rays. 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.



In summary, the proposed thesis project will implement the real-time search for transient high-energy gamma-ray sources directly after the detection of a gravitational wave or an astrophysical neutrino. If found, the combined observations will (for the first time ever) unequivocally prove the existence of a high-energy cosmic ray accelerator related these violent multi-messenger phenomena.



During the proposed thesis project several out of these items can be explored

- Searches for gamma-ray counterparts of Gravitational Waves (GW)

o Optimization of the H.E.S.S. response to GW alerts

o Dedicated data analysis combining H.E.S.S. and HAWC data

- Searches for gamma-ray counterparts of High-Energy Neutrinos

o Analysis of H.E.S.S. and HAWC data obtained in coincidence with neutrino telescopes

- Searches for gamma-ray counterparts of Fast Radio Bursts (FRBs)

o Extension of the H.E.S.S. FRB program towards SKA

- Preparation and implementation of multi-messenger analyses using CTA data

o Optimization of the CTA response to multi-messenger alerts

o Analysis of the first CTA data



The PhD student will become a member of the H.E.S.S., HAWC and CTA collaborations. He/she will participate and later lead the preparation of observation proposals in close collaboration with external partners and will be in charge of the subsequent data analysis. Participation in the onsite operation of the experiments in Namibia and Mexico as well as the data calibration is foreseen. The student will have an extensive set of data analysis tools at his disposal but will also have the opportunity to develop novel methods and techniques taking full advantage of the information provided by multiple messengers. These novel techniques will be applied and tested to H.E.S.S. and HAWC data before being transferred to CTA. Analysis of the first CTA physics data will conclude the thesis project opening multiple possibilities for further studies and employments.

The PhD student will evolve within the astroparticle physics group at Irfu/CEA-Saclay, which is one of the major groups within H.E.S.S. and CTA. Interaction with external partners and members of other collaborations (Desy-Zeuthen/Berlin, MPIK/Heidelberg, PennState/US, Univ. Alberta/Canada, etc.) will allow the student to enlarge his horizon and become a key member of the new and rapidly growing multi-messenger community.

The thesis director (fabian.schussler@cea.fr) is member of the H.E.S.S., HAWC, CTA and ANTARES collaborations. He is the official H.E.S.S. contact for multi-messenger studies, leads several working groups on neutrino/GW-gamma ray correlations involving various observatories and participates in the definition of the science case and the real-time analysis framework for CTA.

Search for primordial black holes with the H.E.S.S. array of Cherenkov telescopes

SL-DRF-18-0261

Research field : Astroparticles
Location :

Service de Physique des Particules (DPHP)

Groupe HESS 2

Saclay

Contact :

Jean-François Glicenstein

Starting date : 01-10-2018

Contact :

Jean-François Glicenstein

CEA - DRF/IRFU/SPP/HESS 2

0169089814

Thesis supervisor :

Jean-François Glicenstein

CEA - DRF/IRFU/SPP/HESS 2

0169089814

H.E.S.S. (High Energy Stereoscopic System) is an Array of Imaging Cherenkov Telescopes located in Namibia and running since a decade. H.E.S.S. is dedicated to the observation of very high energy gamma rays (above 50 GeV). These photons allow identifying and mapping high energy charged cosmic ray sources, among which black holes. The aim of this thesis is to search for primordial black holes. The first results from the VIRGO and LIGO collaborations show that the black hole mass distribution is far from understood. In particular, some exotic black holes could have masses much smaller than ordinary stellar of supermassive black holes and could have been produced in large quantities in the early universe. In some mass range, primordial black holes could account for the dark matter of the Universe. Promirdial black holes with small enough mass evaporate on time scales comparable to the age of the Universe (by emitting Hawking radiation) and give a very short (a few second) burst of high energy photons which can be detected by instruments such as the H.E.S.S. array of Cherenkov telescopes. Primordial black holes with larger masses can also be searched for with other methods, e.g. gravitational lensing.





Searching for double beta decay with scintillating bolometers

SL-DRF-18-0328

Research field : Astroparticles
Location :

Service de Physique des Particules (DPHP)

Groupe Edelweiss

Saclay

Contact :

Claudia Nones

Starting date : 01-10-2018

Contact :

Claudia Nones

CEA - DRF/IRFU/SPP/Edelweiss

0169083520

Thesis supervisor :

Claudia Nones

CEA - DRF/IRFU/SPP/Edelweiss

0169083520

Personal web page : http://irfu.cea.fr/Pisp/claudia.nones/

Laboratory link : http://irfu.cea.fr/Spp/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3900

Exoplanets, planetary system evolution, interaction host star-planets, Tides, Magnetism, MHD

SL-DRF-18-0776

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire Dynamique des Etoiles et de leur Environnement

Saclay

Contact :

Stéphane MATHIS

Allan Sacha BRUN

Starting date : 01-10-2018

Contact :

Stéphane MATHIS

CEA - DRF/IRFU/DAp/LDE3

0169084930

Thesis supervisor :

Allan Sacha BRUN

CEA - DSM/IRFU/DAp/LDE3

+33 1 69 08 76 60

Laboratory link : http://irfu.cea.fr/dap/LDEE/index.php

Since 1995, we have detected planets around about 2800 stars. At least 20% of these stars actually host more than one planet (http://exoplanet.eu/). The architecture of the observed compact systems today – essential for the habitability of exoplanets, and the rotational state of the planets is the outcome of a joint complex evolution of the host star and its orbiting planets.

The aim of this PhD is 1) to model the dynamics of the atmosphere in interaction with its environment by using ab-initio models for the tidal interactions and magnetic interactions and derive prescriptions for the atmospheric mass loss and the tidal torque applied on the planet; and 2) to use the derived prescriptions to improve the physics taken into account in models of the orbital and rotational evolution of planets in multi-planet systems.

Cosmological analysis of the XXL cluster survey

SL-DRF-18-0565

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

Marguerite PIERRE

Starting date : 01-09-2018

Contact :

Marguerite PIERRE

CEA - DRF/IRFU/SAp/LCEG

0169083492

Thesis supervisor :

Marguerite PIERRE

CEA - DRF/IRFU/SAp/LCEG

0169083492

Personal web page : htt://irfu.cea.fr/xxl

Laboratory link : http://irfu.cea.fr/Sap/

Clusters of galaxies are – along with supernovae, CMB and baryonic acoustic oscillations – are a major probe for the various cosmological scenarios. In particular, cluster number counts are very sensitive to the Dark Energy equation of state that depends on the volume (geometrical effects) and on the growth rate of the structures (gravitational effect). Currently, several cluster studies show a puzzling tension with the cosmological parameters derived from the CMB.



The thesis will take place within the framework of the XXL project, which is the largest extragalactic survey performed by XMM (50 deg2), the X-ray satellite of the European Space Agency. The ultimate goal is toe constrain the dark energy equation of state using the some 500 clusters of galaxies newly discovered in the survey. In addition to the X-ray band, numerous observations are available in other wavebands (infrared, optical, millimetre, radio) as well as high-resolution numerical simulations. The XMM observations were performed from 2011 to 2013 and the first series of 14 publications involving limited bright samples was published in 2016.

The proposed thesis is particularly timely because cluster counts from two different surveys, with very different detection methods and mass ranges (Planck S-Z 2015 article XXIV ; XXL 2016 article II) appear to be incompatible with CMB cosmology. The work will take place during the final phase of the project and consists in a detailed study of the parameters impacting on the cosmological analysis. This regards especially the evolution of the cluster physical properties that influence their detection as well as their mass estimates. The final goal will be to adequately model these factors in the global cosmological analysis, extending the current results with 100 clusters to the complete sample of some 500 clusters.



Tools that will be used during the thesis work:

Cluster evolutionary models; X-ray pipeline; multi-wavelength observations of clusters; results from numerical simulations.

Cosmological analysis package; it follows an original method developed at Saclay, based on the forward modelling of the X-ray observable parameters.



All is available and the student will have to get rapidly acquainted to them.



Working context: worldwide consortium gathering some 100 scientists and organised in well-defined sub-projects.

http://irfu.cea.fr/xxl

See page ‘publications’ for detailed presentations of the XXL early results at international conferences.

References for the cosmological code :

https://arxiv.org/abs/1609.07762

https://arxiv.org/abs/1710.01569



We are seeking excellent candidates and having a good practice of English.

From data to theoretical cosmology: likelihood development for future surveys like Euclid.

SL-DRF-18-0670

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Valeria Pettorino

Starting date : 01-10-2018

Contact :

Valeria Pettorino

CEA - DRF/IRFU/SAp/LCS

Thesis supervisor :

Valeria Pettorino

CEA - DRF/IRFU/SAp/LCS

Personal web page : http://www.cosmostat.org/people/valeria-pettorino

Laboratory link : http://www.cosmostat.org/

The nature of Dark Energy (DE), responsible for the accelerated expansion of the Universe, is the

main puzzle of nowadays cosmology. Whether it is a constant or a fluid or a hint that gravity and

Einstein’s theory of General Relativity have to be modified (Modified Gravity, MG) at very large

scales, remains unknown. To solve this fundamental problem, the community has run many

observational projects and a large amount of data will become available in the next few years

from a variety of probes.

The PhD hired within this project will be at the interface between theory and observations to get

the best scientific return out of the big investment done, in particular in Europe.

Objectives include: i) developing the likelihood to analyze data from missions like CFIS, Euclid,

participating to both missions ii) comparing new available data to general theoretical approaches

to understand the nature of DE and MG iii) combining different probes to detect, constrain or

exclude classes of models.

Ultimately, this will allow confirming or disproving the standard theory of Einstein, leading to

new insights in fundamental physics.

Influence of protostellar jets on the formation of stellar clusters

SL-DRF-18-0737

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire de Théorie et de Modélisation

Saclay

Contact :

Patrick Hennebelle

Starting date : 01-09-2018

Contact :

Patrick Hennebelle

CEA - DSM/IRFU/SAp

0169089987

Thesis supervisor :

Patrick Hennebelle

CEA - DSM/IRFU/SAp

0169089987

The gravitational universe: searching for progenitors of gravitational waves

SL-DRF-18-0717

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Sylvain CHATY

Starting date : 01-10-2018

Contact :

Sylvain CHATY

Université Paris Diderot et Institut Universitaire de France - LEPCHE/Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie

01 57 27 53 04

Thesis supervisor :

Sylvain CHATY

Université Paris Diderot et Institut Universitaire de France - LEPCHE/Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie

01 57 27 53 04

Personal web page : www.linkedin.com/in/sylvainchaty

Laboratory link : irfu.cea.fr/Sap

More : www.apc.univ-paris7.fr/APC_CS

The discovery, by the LIGO-Virgo collaboration on Sept. 14th 2015, of gravitational waves (GW) from the merger of two stellar-mass black holes, applauded by the whole scientific community, was unexpected in terms of astrophysical sources: two such heavy stellar-mass black holes (~30 solar masses) had never been seen before, although they likely constitute the tip of the iceberg. From this detection, several questions immediately arose: how can such black holes form, and how many are there in our local Universe and beyond? The second breakthrough came with the detection of a kilonova associated with the merger of two neutron stars, on Aug. 17th 2017. Further questions arose, such as the nature of the outcome of such a merger. More generally, one of the most fundamental questions in terms both of astrophysics and physics, concerns the nature of the progenitors for this type of system. Finally, we now know that many such mergers will be detected by current and future GW observatories, but we do not know the exact rate.



Stellar binaries hosting compact objects (especially neutron stars and black holes) constitute the best progenitors, evolving until eventually merging in binary black holes (BBH), binary neutron stars (BNS) or black hole/neutron star binaries (BH/NS), and emitting GW. The overall evolution of such binaries is still subject to many uncertainties about some parameters of binary evolution, such as: the natal kick received during each supernova event, metallicity effect on stellar wind, common envelope phase, conditioning the survival of the system, spin of each component, etc…

Sparse semi-parametric recovery of astronomical radio-images

SL-DRF-18-0561

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Jean-Luc STARCK

Starting date : 01-10-2018

Contact :

Jean-Luc STARCK

CEA - DSM/IRFU/SAp/LCS

01 69 08 57 64

Thesis supervisor :

Jean-Luc STARCK

CEA - DSM/IRFU/SAp/LCS

01 69 08 57 64

Personal web page : http://jstarck.cosmostat.org

Laboratory link : http://www.cosmostat.org

Radio-astronomy is entering the golden age, with new very sensitive instruments such as LOFAR, LWA and SKA). This allows us to reinvestigate the radio emission from ground. At these frequencies, both the close and distant universe can be studied. Radio instruments require however to reconstruct first images from a subset of Fourier components. Very nice progress have been made in the recent years in this domain, thanks to recent breakthrough in applied mathematics such sparse theory and compressed sensing theories [1,2]. Once the images are restored, the second phase can start, consisting generally in detecting sources and deriving their electromagnetic spectrum. The challenge is also to be able to process very large images of 10k x 10k pixels and to take at the same time into account Direction Dependent Effects (DDE).

The goal of this PhD thesis is to propose a new framework for analysing radio data set, where restoration and interpretation steps are done jointly. This involves a semi-parametric approach where regularisation is performed in the parameters space.





References:

H. Garsden, J. Girard, J.-L. Starck, S. Corbel, C. Tasse et al, "LOFAR Sparse Image Reconstruction", Astronomy and Astrophysics, 575, A90, 2015.

M. Jiang, J. Bobin and J.-L. Starck, "Joint Multichannel Deconvolution and Blind Source Separation", SIAM Journal on Imaging Sciences, 10, 4, pp. 1997-2021, 2017.

Study and use of the SPICA polarimetric bolometers for submillimeter astrophysics from ground and stratospheric balloons.

SL-DRF-18-0428

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire de Détection Spatiale

Saclay

Contact :

Vincent REVERET

Louis RODRIGUEZ

Starting date : 01-10-2018

Contact :

Vincent REVERET

CEA - DSM/IRFU/SAp/LSIS

01 69 08 74 02

Thesis supervisor :

Louis RODRIGUEZ

CEA -

More : http://irfu.cea.fr/Sap/

The Herschel submillimeter space observatory has revolutionized some areas of astrophysics, such as star formation, showing that stars are formed mainly in filaments of gas and dust. This rises an important question on the role of the magnetic field within these structures that cannot be solved by the current astrophysical instruments. The Safari-Pol instrument, installed on the future SPICA international space observatory and proposed by CEA Saclay, will be able to detect a wide variety of far-infrared filaments, as well as their possible associated magnetic field (through the polarization of the light coming from these regions).

Safari-Pol will contain 3 focal planes of cryogenic silicon bolometers currently developed by CEA (LETI and Saclay). These are innovative detectors, operating at 50 mK, with a very high sensitivity. Each pixel is intrinsically sensitive to the polarization of incident radiation.

For this thesis, the first step will be to model, and test the bolometers of Safari-Pol (measurement of sensitivity, time constant, cross-polarization, etc ...). Then, the candidate will propose and test one or more technological solutions to match the conditions of observation on a stratospheric balloon and on a ground-based telescope which are perfectly complementary to the space-based observations. This work will be accompanied by a study of the possible observation modes (ground-based and balloon-borne) and their expected performances.

Physico-chemical properties in protostellar cores: characterization of the coupling between magnetic field and circumstellar matter

SL-DRF-18-1026

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire d’études de la formation des étoiles et du milieu interstellaire

Saclay

Contact :

Anaëlle MAURY

Starting date : 01-10-2018

Contact :

Anaëlle MAURY

CEA - DRF/IRFU/SAp/LFEMI

0169089570

Thesis supervisor :

Anaëlle MAURY

CEA - DRF/IRFU/SAp/LFEMI

0169089570

Personal web page : http://irfu.cea.fr/Pisp/anaelle.maury/

Laboratory link : http://irfu.cea.fr/dap/

The PhD project main goal is to test the physicochemical conditions in the inner parts of the protostellar cores, where young stars are forming.

Knowing the physical conditions in these regions is of uttermost importance if one wants to understand the coupling between the magnetic field in the core and the infalling material feeding the protostar, and ultimately constrain the role of magnetic field during the formation of solar-type stars.



We have a large ALMA dataset, including observations of several molecular species, in a closeby protostar. The PhD project will aim at analyzing these data, interpret them together with the magnetic field map we have obtained, and finally compare the local conditions and magnetic braking efficiency to predictions from MHD numerical models with radiative transfer.

The physics of giant star-forming regions in primordial galaxies from a synergy of observations and simulations.

SL-DRF-18-0323

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

Frédéric BOURNAUD

Starting date : 01-10-2018

Contact :

Frédéric BOURNAUD

CEA - DRF/IRFU/SAp/LCEG

01 69 08 55 08

Thesis supervisor :

Frédéric BOURNAUD

CEA - DRF/IRFU/SAp/LCEG

01 69 08 55 08

The physics of giant star-forming regions in primordial galaxies from a synergy of observations and simulations --





The morphology of star forming galaxies in the distant Universe at redshift z=1-3, is remarkably different from that of nearby spirals. They have irregular morphologies, often dominated by giant star forming regions dubbed « giant clumps ». This is thought to be driven by their very large gas fractions and strong turbulence: gas-rich galaxies can become violently unstable and fragment in such giant clumps.



However, a quantitative understanding of the nature and physical properties of these clumps is still lacking Hotly debated topics of contending remain, regarding the distribution of clumps masses, star formation rates, sizes, clumps formation rates and lifetime. It also remains unknown whether they survive stellar feedback processes, in which case they can drive the growth of galactic bulges and the fueling of supermassive black holes at the center of galaxies.



We propose a PhD project to explore a state of the art approach to this topic, tracking 3 complementary lines of research on:

1) the physical characterization of clumps properties from observations,

2) systematic and quantitative comparison of observations to simulations,

3) running suites of very high resolution numerical simulations with an improved modeling of star formation and feedback.



These complementary lines will bring a robust understanding of the nature of the giant clumps and their role in shaping disks, bulges and central black holes. They will also provide a new way to constrain the gas fraction in galaxies at various epochs, which is another highly debated issue in galaxy formation. The proposed work will ideally prepare future developments with the use of JWST, and comparison to forthcoming ALMA data. The proposed thesis will also employ numerical simulations performed on the largest supercomputers in France and Europe.

Study of interstellar grains in the JWST era

SL-DRF-18-0283

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire d’études de la formation des étoiles et du milieu interstellaire

Saclay

Contact :

Frédéric Galliano

Starting date : 01-10-2018

Contact :

Frédéric Galliano

CNRS - DSM/IRFU/SAp/LCEG

01 69 08 18 21

Thesis supervisor :

Frédéric Galliano

CNRS - DSM/IRFU/SAp/LCEG

01 69 08 18 21

The interstellar medium, filling the volume between the stars of a galaxy, is constituted of two main components: gas and dust. Dust grains are small solid particles, mainly composed of silicate and carbonaceous materials. They play a major role in the physics of the interstellar medium, although accounting for only one percent of its mass. Indeed, they absorb, and reemit in the infrared, an important fraction of the power radiated by stars and accretion disks. In particular, star forming regions are completely opaque in visible light. Only the infrared radiation, emitted at 99% by dust, allows us to study them. Grains are also responsible for the gas heating by photoelectric effect, in photodissociation regions (PDR). Finally, grains are catalysts of numerous chemical reactions, including the formation of dihydrogen, the most abundant molecule in the universe.



The properties of these dust grains (abundance, chemical composition, size distribution, etc.), as well as their evolution, are, however, still poorly known. This is the direct consequence of the complexity of this component and of the lack of observations discriminating different models. These uncertainties are affecting numerous aspects of our knowledge in astrophysics: mass measurements, unreddening (i.e. correction of the extinction along the line of sight), detailed PDR models, etc. Refining our understanding of dust is also crucial to understand the interstellar lifecycle, as grains regulate several processes controlling this cycle. An accurate understanding of grain

physics is thus necessary to understand galaxy evolution.



An approach, to tackle these open questions, consists in studying the way observed grain properties vary with the physical conditions they experience. Such empirical relations, if they are precise enough, allow us to remove some degeneracies on different models. The thesis that we are proposing focuses on the detailed study of the smallest grains (radius < 10 nm) and polycyclic aromatic hydrocarbons (PAH). These components of the interstellar medium radiates out-of-equilibrium in the mid-infrared (5–40 microns). This is the wavelength domain that contains most of the solid state resonance features.



This study will focus on several nearby galaxies, including the Magellanic clouds. The interest of nearby galaxies compared to the interstellar medium of our galaxy resides in the diversity of physical conditions (metallicity, radiation field intensity, etc.)



Several studies have already been published on this topics, especially with the Spitzer space telescope. However, most have been somehow superficial. Numerous aspects remain to be studied: (i) the correlation of the main aromatic bands with the physical conditions; (ii) constraining the evolution of their size distribution; (iii) identifying and modelling several bands of solids in star forming regions. One of the originalities of this thesis will consist in developing a sophisticated method to model the data. Indeed, most previous studies have performed simple linear decompositions. We propose that the student develop a hierarchical Bayesian decomposition code to analyze infrared spectra, with constraints provided by atomic, molecular and solid-state databases. This type of code allows to physically model the sample and to statistically model the distribution of parameters, simultaneously. It allows us to remove several degeneracies and to

extract the maximum information from the data, taking into account the various sources of uncertainties, without overinterpreting the observations. We have recently developed such a code to model spectral energy distributions, and the results are convincing. This new tool and its meticulous application to the data are the warranty of a precise and original interpretation of the physical processes taking place in the studied regions.



The James Webb Space Telescope (JWST), which will be launched in 2019, will observe the mid-infrared domain with

unprecedented sensitivity and saptial resolution. The methods developed during the thesis could be applied to these new data.

The Univers with MeerKAT: searching for explosive and exotic high energy transients.

SL-DRF-18-0657

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Stéphane CORBEL

Starting date : 01-09-2018

Contact :

Stéphane CORBEL

Université Paris 7 - DRF/IRFU/SAP/LEPCHE

01 69 08 45 62

Thesis supervisor :

Stéphane CORBEL

Université Paris 7 - DRF/IRFU/SAP/LEPCHE

01 69 08 45 62

Laboratory link : http://www.thunderkat.uct.ac.za/

More : https://arxiv.org/abs/1711.04132

The role of gas and star formation inside the first forming galaxy structures

SL-DRF-18-0910

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)

Saclay

Contact :

Emanuele DADDI

Starting date : 01-10-2018

Contact :

Emanuele DADDI

CEA - DRF/IRFU/SAp

Thesis supervisor :

Emanuele DADDI

CEA - DRF/IRFU/SAp

At redshifts of z=2 to 3, the epoch of the peak star formation and black hole activity in the Universe, the first giant dark matter halos were also growing very rapidly, and baryons falling into their deep potential wells induced prodigiously vigorous activity leading to the major phases of galaxy and black hole assembly, often hidden by dust. These early phases for the evolution of galaxies are expected to be crucial to lead to the formation of their dominant early type galaxy population (via quenching mechanisms still poorly understood) and well relaxed hot gas atmospheres, as observed in local massive galaxy clusters (via some sort of yet unknown feedback between galaxies and the hot gas, leading to energy and entropy injection affecting its thermodynamic evolution). The overall physical processes relevant for galaxies and structures evolution in the first forming clusters are still largely poorly mapped, and yet not well understood. But increasing interest and efforts in the community coupled with emerging observational results and prospects for future mission (e.g., JWST, Euclid and Athena) make this research field one of the most hot and promising in the current domain of galaxies and structure formation. I propose a PhD thesis in Saclay in this research field, based on new observations with ALMA, NOEMA, Herschel, HST and Keck of two dense structures discovered by our research groups at z=2 and 2.5 (Gobat et al 2011; 2013; Wang et al 2016) and a new forming cluster found at z=2.91. The student will be responsible of the final reduction, analysis and interpretation of a substantial amount of data we obtained

with the new and revolutionary Keck Cosmic Web Imager, allowing for the first time 3D spectroscopy in the blue over large fields, down to wavelengths not accessible to the MUSE instrument at the VLT. These Keck data have revealed giant clouds of cold gas extending over 100kpc or more at the cluster cores, detected from their Lya emission. The high level goal of the thesis will be to observationally characterise and understand the nature, origin and fate of these giant reservoirs of cold gas. This will be done in particular in connection with galaxy activity present in the clusters, that will be probed by HST multicolour imaging (to reveal morphologies, stellar populations and merging rates possibly connected to galaxy stripping and production of inter cluster material) and with NOEMA, ALMA and Herschel (to study gas reservoirs, star formation hidden by dust and the state of the interstellar medium). The cold gas might eventually result to be a first convincing smoking gun of cold flow accretion to massive dark matter halos required by theory to justify the vigorous galaxy activity present at high redshift. Such smoking gun has long been sought observationally at high redshifts but never convincingly detected yet. Possible evidences leading to this could be connected with the morphology of the Lya gas, large kinematics and metal enrichment, that we will be able to investigate with existing data and with future observations. The student will be, in fact, involved during the PhD in a vigorous effort of proposing for Keck, VLT and ALMA/NOEMA time, to foster this science, with a resulting expertise in all aspects of observational astronomy, including experience with dealing with truly multi-wavelength datasets.

Central engine of extreme explosions: magnetic field amplification in proto-neutron stars

SL-DRF-18-0298

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire de Théorie et de Modélisation

Saclay

Contact :

Jérôme Guilet

Thierry FOGLIZZO

Starting date : 01-10-2018

Contact :

Jérôme Guilet

CEA - DRF/IRFU/SAp/LTM

01 69 08 04 37

Thesis supervisor :

Thierry FOGLIZZO

CEA - DRF/IRFU/SAp/LTM

01 69 08 87 20

Personal web page : http://wwwmpa.mpa-garching.mpg.de/~jguilet/

Laboratory link : http://irfu.cea.fr/Sap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=1250

More : http://irfu.cea.fr/Sap/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=4201

The collapse of the iron core of massive stars gives rise to some of the most violent explosions of the universe. The physical mechanism driving these explosions is, however, not well understood and its theoretical description is one of the big challenges of modern astrophysics. The most extreme of these explosions - in terms of kinetic energy or luminosity - suggest the likely presence of a rapid rotation as well as a strong magnetic field which can efficiently extract this large kinetic energy reservoir. They could indeed correspond to the birth of the most magnetised neutron stars, called magnetars, which dipolar magnetic field of the order of 10^15 G is the most intense known in the present universe. This PhD project will endeavour to answer one major open question: the origin of this extreme magnetic field. The process widely considered as the most probable source of this magnetic field is the development of a magnetohydrodynamic instability called the magnetorotational instability (MRI). Numerical simulations of a small patch of a forming neutron star have demonstrated an efficient amplification of the magnetic field (e.g. Guilet & Müller 2015). This PhD project aims at determining for the first time the efficiency at generating a large-scale magnetic field coherent over the whole neutron star. This is crucial both for the launch of the explosion and to explain the properties of galactic magnetars. The project will consist primarily in developing numerical simulations of a global model of a proto-neutron star with the code MagIC. These simulations will allow to study the development of the magnetorotational instability with a focus on the generation of a large-scale magnetic field. These results will then be used to develop an analytical prescription of the magnetic field amplification that can be used in a model of the full explosion.

Cosmological constraints from the large scale quasar surveys of eBOSS and DESI

SL-DRF-18-0294

Research field : Astrophysics
Location :

Service de Physique des Particules (DPHP)

Groupe Bao

Saclay

Contact :

Etienne Burtin

Starting date : 01-10-2018

Contact :

Etienne Burtin

CEA - DRF/IRFU/SPP

0169085358

Thesis supervisor :

Etienne Burtin

CEA - DRF/IRFU/SPP

0169085358

Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=3428

The observation of the acceleration of the expansion of the Universe has triggered a wide research program in order to identify and understand the phenomenon of 'dark energy'.



For the last ten years, the imprint of baryonic acoustic oscillations (BAO) on the galaxy spatial distribution has been used as a 'standard ruler' to probe the geometry of the Universe and to constrain the cosmological parameters. At present, the community os converging towards the use of the full anisotropic clustering of tracers of matter to fully constrain the expansion rate of the Universe and to test possible modifications of gravity through the measurement of the growth rate of cosmic structures.



To perform these measurements, we use the data from the large spectroscopic surveys eBOSS (2014-2019) and DESI (2019-2025). These surveys allow for the measurement of the redshift (z) of millions of astrophysical objects for which we can build a 3D map of the matter distribution in the Universe. In the proposed subject, we will use the quasars, the brightest sources of light, to probe the Universe in an almost unexplored redshift domain 0.8


Furthermore, the correlation between quasars and other cosmological probes such as the lensing of the cosmic microwave background is a way to access new observables. This is a promising technique to test potential modifications of general relativity.

SL-DRF-18-0550

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire d’études de la formation des étoiles et du milieu interstellaire

Saclay

Contact :

Philippe ANDRE

Philippe ANDRÉ

Starting date : 01-10-2018

Contact :

Philippe ANDRE

CEA - DRF/IRFU/SAp/LFEMI

Thesis supervisor :

Philippe ANDRÉ

CEA - DRF/IRFU/SAp/LFEMI

0169089265

A search for gamma ray bursts with CTA

SL-DRF-18-0269

Research field : Astrophysics
Location :

Service d'Astrophysique (DAP)

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Thierry STOLARCZYK

Starting date : 01-09-2018

Contact :

Thierry STOLARCZYK

CEA - DRF/IRFU/DAp/LEPCHE

+33 1 69 08 78 12

Thesis supervisor :

Thierry STOLARCZYK

CEA - DRF/IRFU/DAp/LEPCHE

+33 1 69 08 78 12

More : http://neutrini.free.fr

The CTA observatory is a next-generation ground-based instrument for exploring the sky in gamma rays at very high energies, with a sensitivity ten times better than the existing and an amazing new capacity for the search of transient source counterparts. The thesis work is a contribution to the performance optimisation of the real-time search strategy for transient sources, in particular gamma ray bursts and gravitational wave counterparts.

Participation in the development of a 30 T REBCO high-field magnet

SL-DRF-18-0437

Research field : Electromagnetism - Electrical engineering
Location :

Service des Accélérateurs, de Cryogénie et de Magnétisme (DACM)

Laboratoire d'Etudes des Aimants Supraconducteurs (LEAS)

Saclay

Contact :

Philippe FAZILLEAU

Véronique AUBIN

Starting date : 01-12-2018

Contact :

Philippe FAZILLEAU

CEA - DRF/IRFU/SACM/LEAS

0169086762

Thesis supervisor :

Véronique AUBIN

CentraleSupelec - MSSMat UMR CNRS 8579

+33 1 75 31 65 20

The work proposed is to design, within the DACM HTS team, a HTS superconducting high-field magnet with a central field of 30 T.

The design part integrates all the usual aspects (conductor, magnetism, mechanics, thermal, stability, protection, detection) by focusing on the specific problems related to HTS tapes (conductor dynamics) and the constraints raised for the insert 10 T NOUGAT (magnetic, detection and mechanics) currently in progress.

Prototypes in REBaCuO will be realised to guide the design of the magnet. They will be tested in a background field at the National Laboratory of Magnetic Fields in Grenoble.

Fundings is foreseen from the National Agency for Research (ANR). This is the natural continuation of the ANR NOUGAT (design and production of an HTS 10 T insert operating in 20 T resisitive) which will end in 2018.

Detection of weak signals in video streams with active reinforcement learning

SL-DRF-18-0761

Research field : Mathematics - Numerical analysis - Simulation
Location :

Service d'Astrophysique (DAP)

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Jean-Luc STARCK

Starting date : 01-10-2018

Contact :

Jean-Luc STARCK

CEA - DSM/IRFU/SAp/LCS

01 69 08 57 64

Thesis supervisor :

Jean-Luc STARCK

CEA - DSM/IRFU/SAp/LCS

01 69 08 57 64

Personal web page : http://jstarck.cosmostat.org

Laboratory link : http://www.cosmostat.org

Video digitizes images and audio streams. It is a cost-effective media for remote vision and for

capturing physical events occurring around us. In recent applications, such as video surveillance,

data streams are processed for finding patterns in order to aid human vision with machine

learning. In other domains, such as Astrophysics, observational tools record phenomena appearing

beyond the visual and audio spectrum, producing data that we could compare to video streams. In

both cases, some people need to spend time observing data streams so as to find special events,

which might be physical risks in sensible places or neutrinos before a red giant star collapses in a

supernova somewhere in the Universe [3]. As Big Data and uninterrupted data flows easily escape

from human attention and understanding, computer vision can massively process these data flows

without interruption.

For identified events, such as fire and flames, computer vision is reliable and efficient as it can

distinguish between flames and fire-colored moving objects, thanks to the use of spatial and

temporal wavelet transforms [4]. Computer vision systems also enable the early detection of

identified events and features, for autonomous vehicles and robots [2]. With unidentified events,

the best way to efficiently detect and identify them remains human observation and analysis. As a

result, detecting and recognizing unidentified events in data streams requires man-machine

collaboration, instead of man-machine competition.

D R F / I R F U

Direction de la Recherche Fondamentale– Institut de Recherche sur les lois Fondamentales de l’Univers

on

Active learning strives towards the collaboration of human intelligence and artificial intelligence.

With supervised models in machine learning and deep learning, items must be previously labelled

by experts and/or people answering to labelling queries – e.g. captcha. Active learning from

relative queries, instead of absolute ones, makes it possible to train machine-learning algorithms

from weak predictors, such as side information or non-experts answers, then to get comparable or

better performance than with the experts’ answers to labelling queries [1]. With such a model,

item recognition relies on human information processing-based inputs, more than on human

knowledge-based inputs.

The IoT and smart cities are going to produce huge and heterogenous datasets, to be compared

with astronomical observations and collected in data lakes. Therefore, the detection of unexpected

and/or unidentified events in data streams should become a significant task, depending on active

learning for the future of society, science, and economy. Finally, detecting weak signals in videos

streams thanks to active learning or other approaches could represent an important stake, while

there currently appears no or few works published on this topic, to our knowledge. It might allow

us to catch unusual phenomenon in video surveillance before specific events occur, so as to

prevent risks. It might also allow cosmologists to be notified of unobserved phenomena that could

require attention, in order to identify and classify them for an active reinforcement learning

process.

The thesis we propose concerns the research and experimentation of both sparse representations

[5] and online models of active learning for the detection of weak signals in data streams. It is

focused on application in video surveillance and astronomical data surveillance. It will be

experimented thanks to Big Data systems and Lambda architecture, allowing to run offline and

online analysis tasks in parallel processes. The candidate should be interested in computer vision,

online analysis and research applications. Candidate preferring a permanent position in private

research after the thesis are welcome (Lead Researcher for online analysis @DATA2B).

References

[1] Qian B., Wang X., Wang F., Li H., Ye J., and Davidson I. Active learning from relative

queries. In Proceedings of the Twenty-Third International Joint Conference on Artificial

Intelligence, IJCAI ’13, pages 1614–1620. AAAI Press, 2013.

[2] Donadio F., Frejaville J., Larnier S., and Vetault S. Human-robot collaboration to perform

aircraft inspection in working environment. In Proceedings of 5th International conference on

Machine Control and Guidance,, 2016.

[3] Antonioli P., Tresch Fienberg R., Fleurot F., Fukuda Y., Fulgione W., Habig A., Heise J.,

McDonald A.B., Mills C., Namba T., Robinson L.J., Scholberg K., Schwendener M., Sinnott

R.W., Stacey B., Suzuki Y., Tafirout B., Vigorito C., Viren B., Virtue C., and Zichichi A. Snews:

the supernova early warning system. New Journal of Physics, 6(1):114, 2004.

[4] Dedeoglu Y. Güdükbay U. & Cetin A. E Töreyin, B. U. Computer vision based method

for real-time fire and flame detection. 1(27):49–58, 2006.

[5] Starck J.-L., Murtagh F, and Fadili J, Sparse Image and Signal Processing: Wavelets and

Related Geometric Multiscale Analysis, Cambridge University Press, Cambridge (GB), 2015

(428-pp).

Simulation and image reconstruction of time-of-flight PET scanners with high spatial resolution

SL-DRF-18-0237

Research field : Medical imaging
Location :

Service de Physique des Particules (DPHP)

Groupe DO

Saclay

Contact :

Viatcheslav SHARYY

Starting date : 01-10-2018

Contact :

Viatcheslav SHARYY

CEA - DSM/IRFU/SPP/CaLIPSO

0169086129

Thesis supervisor :

Viatcheslav SHARYY

CEA - DSM/IRFU/SPP/CaLIPSO

0169086129

Personal web page : http://irfu.cea.fr/Spp/Phocea/Pisp/index.php?nom=viatcheslav.sharyy

Laboratory link : http://irfu.cea.fr/Spp/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3730

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 with the energy 511 keV 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). The time-of-flight (TOF) technique is used to improve the signal-to-noise ratio in full body scans and therefore the image quality. This technique measures the difference in time between the two annihilation photons in addition to their position. Currently the new type of scanner is under development at IRFU, CEA Saclay. This scanner will combine the possibility acquire images with a high spatial precision of 1 mm³ using the TOF capability (time resolution better than 150 ps) thanks to photons produced by the Cherenkov effect.

In this thesis we propose to develop a simulation of the foreseen detector, to measure the main detector performances, to work on the development of the image reconstruction algorithms and adapt them to scanners with the high precision.

Detectors for time-of-flight PET imaging with high spatial resolution

SL-DRF-18-0238

Research field : Medical imaging
Location :

Service de Physique des Particules (DPHP)

Groupe DO

Saclay

Contact :

Viatcheslav SHARYY

Dominique YVON

Starting date : 01-10-2018

Contact :

Viatcheslav SHARYY

CEA - DSM/IRFU/SPP/CaLIPSO

0169086129

Thesis supervisor :

Dominique YVON

CEA - DSM/IRFU/SPP/CaLIPSO

01 6908 3625

Personal web page : http://irfu.cea.fr/Spp/Phocea/Pisp/index.php?nom=dominique.yvon

Laboratory link : http://irfu.cea.fr/Spp/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3730

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). In this thesis we propose to develop a detector based on crystalline Cherenkov radiators. We have selected technologies that are particularly effective for PET imaging. The thesis will consist in measuring the properties of scintillating crystals, in the assembly and characterization of complete detector modules. This involves commissioning of the measuring equipment, data processing and the development of Monté-Carlo simulations using GATE software and the comparison of obtained results with experimental measurements.

The principles of the detector are patented. They will allow one to produce neurological PET with highly improved performances.

Bridging ab initio and energy density functional methods for atomic nuclei

SL-DRF-18-0212

Research field : Nuclear Physics
Location :

Service de Physique Nucléaire (DPHN)

Groupe Structure Noyau

Saclay

Contact :

Vittorio SOMA

Thomas DUGUET

Starting date : 01-10-2018

Contact :

Vittorio SOMA

CEA - DRF/IRFU/SPhN/Structure Noyau

0169083236

Thesis supervisor :

Thomas DUGUET

CEA - DRF/IRFU/SPhN/Structure Noyau

0169082338

Laboratory link : http://irfu.cea.fr/Sphn/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=4070

Phenomena involving atomic nuclei, from nuclear reactors to neutron star coalescence, involve various properties of nuclei, many of which remain inaccessible to experiments. Theoretical models are therefore needed to extrapolate and predict in a robust way their behaviors. However, the atomic nucleus, a many-body quantum system governed by the strong interaction, is one of the most complex objects to model in physics: Today there is no unified theory of atomic nuclei. Their description is carried out either by ab initio methods or by more effective approaches, such as the energy functional Method (EDF). The former provide an elementary description rooted in the underlying theory of the strong interaction and their predictions are more robust by construction, with better controlled errors. The latter are applicable to a much larger number of nuclei due to a lower numerical cost, but the current implementations of the EDF method are highly phenomenological and do not have the reliability of ab initio methods. Taking place within the frame of a long-term research program between CEA Saclay and CEA Bruyères-le-Chatel, the project consists of developing an "ab initio-driven energy density functional method" that is meant to be eventually reliable and systematically improvable. This is of interest both for fundamental nuclear structure studies of next generation and to render ingredients of reaction models, e.g. for neutron-nucleus inelastic scattering, more consistent and reliable on the long run. Building on a first step that was restricted to semi-magic nuclei, the goal is to extend the approach to doubly open-shell nuclei that constitute the vast majority of (known or yet unknown) systems over the nuclear chart. The work will consist in formal developments, computational tasks and application of the new technology to cases of experimental interest. International collaborations are foreseen. A preparatory 3-month internship is envisaged.

Shape evolution in exotic neutron-rich nuclei

SL-DRF-18-0285

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPHN)

Groupe Structure Noyau

Saclay

Contact :

Wolfram KORTEN

Starting date : 01-10-2018

Contact :

Wolfram KORTEN

CEA - DSM/IRFU/SPhN/Structure Noyau

+33169084272

Thesis supervisor :

Wolfram KORTEN

CEA - DSM/IRFU/SPhN/Structure Noyau

+33169084272

Personal web page : https://www.researchgate.net/profile/Wolfram_Korten

Laboratory link : http://irfu.cea.fr/Sphn/Phocea/Vie_des_labos/Ast/ast_sstheme.php?id_ast=293

More : https://www.phy.anl.gov/atlas/

One of the most fundamental properties of the atomic nucleus is its shape, which is governed by the interplay of macroscopic, liquid-drop like properties of the nuclear matter and microscopic shell effects, which reflect the underlying nuclear interaction. In some cases, configurations corresponding to different shapes may coexist at similar excitation energies, which results in the wave functions of these states mixing. Experimental observables such as quadrupole moments and the electromagnetic transition rates between states are closely related to the nuclear shape. The experimental determination of these observables, therefore, represents a stringent test for theoretical models.

This thesis is integrated in our ongoing programme to study nuclear shapes by means of Coulomb excitation and more specifically such an experiment is planned on 100Zr. This method allows to extract the excitation probability for each excited state and to extract a set of electro magnetic matrix elements, and in particular the quadrupole moment which determines the shape of the nucleus. The radioactive 100Zr beam is provided by the ATLAS-CARIBU facility at Argonne National Laboratory (ANL), which is currently the only facility world-wide able to deliver beams of such refractory elements. The programme advisory committee has already accepted the experiment with high priority and we expect it to be scheduled in 2018 or (early) 2019. The PhD student will participate in the preparation and setting-up of the experiment. It would be advantageous if he/she started already working on the subject already during the stage M2. He/she will be responsible for the data analysis, the presentation of the scientific results (at conferences or workshops) and their publication in a scientific journal. During the thesis work the PhD student may also participate in other experiments of the research group. All experiment(s) take place in international collaborations and may require prolonged stays at foreign laboratories (e.g. 4-6 weeks at ANL, USA).

Quarkonium production in lead-lead at the LHC with ALICE

SL-DRF-18-0407

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPHN)

Groupe ALICE

Saclay

Contact :

Javier CASTILLO

Starting date : 01-10-2018

Contact :

Javier CASTILLO

CEA - DRF/IRFU/SPhN/ALICE

+33 169087255

Thesis supervisor :

Javier CASTILLO

CEA - DRF/IRFU/SPhN/ALICE

+33 169087255

Laboratory link : http://irfu.cea.fr/Sphn/Alice/

More : http://alice-collaboration.web.cern.ch

A few microseconds after the Big Bang, the Universe was in a Quark-Gluon Plasma (QGP) state. This state, predicted by the Quantum Chromodynamics, the theory of the strong interaction, is reached for very high temperatures or energy densities. This conditions are obtained in ultrarelativistic heavy-ion collisions at the CERN LHC. The study of the quarkonia production, bound states of heavy quarks (charm c-cbar or beauty b-bbar), is particularly relevant to understand the QGP properties. Quarkonia are rare and heavy particles which are produced in the initial stages of the collision, even before the QGP is formed 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. At the LHC, Upsilons (b-bar) and the J/psis (c-cbar) are complementary, the former are best suited to study the sequential suppression and the latter should allow the study of an eventual regeneration mechanism (formation of quarkonia by quark recombination in the QGP).

Our team is composed of 6 full time physicist, one PhD student, as well as about ten engineers and technicians. The Saclay group has important responsibilities within the ALICE Collaboration, among which is the coordination of all quarkonium analyses and is well recognised for its many contributions in hardware and software development, data analyses, etc …

We propose to study the production of quarkonia in Pb-Pb collisions at the highest LHC energies. Quarkonia will be measured via their dimuon decay channel with the muons being reconstructed in the ALICE muon spectrometer.

Since 2015 the LHC is running at almost a factor of two higher energy than during run 1. In 2015 ALICE accumulated three times more Pb-Pb collisions than during run 1 and at the end of 2018 a new Pb-Pb data taking period will at least double the available data set. This data will allow the student to carry a detailed analysis of the production of the various quarkonium states. The student will also participate to the efforts of our laboratory on the upgrade program of the muon spectrometer during the long shutdown 2 in view of the runs 3 and 4 off the LHC

DEVELOPMENT OF THE ALICE MUON FORWARD TRACKER (MFT) DETECTOR

SL-DRF-18-0342

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPHN)

Groupe ALICE

Saclay

Contact :

Stefano PANEBIANCO

Alberto Baldisseri

Starting date : 01-10-2018

Contact :

Stefano PANEBIANCO

CEA - DRF/IRFU/SPhN/ALICE

0169087357

Thesis supervisor :

Alberto Baldisseri

CEA - DRF/IRFU/SPhN/ALICE

+33 169089333

The ALICE experiment at LHC, which is fully devoted to the study of the Quark Gluon Plasma, is pursuing an ambitious program of upgrades for the futur Runs 3 and 4. In particular, a new forward tracker, the MFT (Muon Forward Tracker), will be installed to detect charged particles close to the point where LHC beams interact, just in front of the present muon spectrometer. The MFT consists of 5 disks equipped with silicon chips, developed with CMOS technology, the most advanced microelectronics technique in the framework of vertex detectors for HEP. The high granularity and extreme position resolution of the detector will open unexplored physics cases for the ALICE experiment.

The PhD student will participate to all phases of the production, qualifications and validation of the MFT elements. In particular, he/she will contribute actively to the study of the MFT ladders which constitues the disks. In addition, he/she is expected to take a leader role in the commissioning of the full detector and in the analysis of its first data.

The understanding of the detector response will be fundamental to improve the geometry description in the MFT Montecarlo and to assess a deep comparison of the simulated performances with the commissioning data.

Depending on the MFT commissioning planning, he/she will study in more detail one physics channel and to perform a data analysis on Run 2 data, in relation with the improvements brought by the presence of MFT in the future

The discovery of the new superheavy elements: development and implementation of new tools

SL-DRF-18-0262

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPHN)

Groupe Structure Noyau

Saclay

Contact :

Barbara Sulignano

Starting date :

Contact :

Barbara Sulignano

CEA - DSM/IRFU/SPhN/LENA

0169 08 42 27

Thesis supervisor :

Barbara Sulignano

CEA - DSM/IRFU/SPhN/LENA

0169 08 42 27

Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=3404

Hunting for super heavy elements is 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)(Figure below) 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 candidate will work on the complete test of the whole focal plane detector, more specifically with the testing and characterization of the double-sided silicon strip detector (DSSD) along with the associated front-end electronics (FPCSA). The student will take an active part in the final tests of the whole SIRIUS detector to be carried out at GANIL under in-beam condition.

The student will also take part in the scientific activities of the group having as primary aim the investigation of nuclear structure in the heavy elements at VAMOS GAS FILLED at GANIL. Indeed, in the next future we will propose a large physics campaign aiming to study, via prompt and decay gamma ray spectroscopy, very heavy elements from Uranium to Rf (Z=104).

Nuclear shape and fission fragment population

SL-DRF-18-0167

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPHN)

Groupe MNM

Saclay

Contact :

Thomas MATERNA

Frank GUNSING

Starting date : 01-10-2018

Contact :

Thomas MATERNA

CEA - DSM/IRFU/SPhN/MNM

0169084091

Thesis supervisor :

Frank GUNSING

CEA - DRF/IRFU/SPhN

01 69 08 75 23

Laboratory link : http://irfu.cea.fr/Sphn/Phocea/Vie_des_labos/Ast/ast_sstheme.php?id_ast=186&id_unit=7&id_groupe=498

More : https://www.ill.eu/fr/instruments-support/instruments-groups/instruments/fipps/description/a-view-of-the-instrument-housing/

Nuclear fission produces in some cases the same nuclei with different shapes (spherical or deformed). This shape coexistence at low excitation energy is maybe linked to different fission modes. The subject of the PhD is to study the production of these nuclei and their shapes in the neutron-induced fission of 233U using the brand new gamma-ray spectrometer FIPPS of the high-flux reactor of Grenoble. The experimental campaign should take place at the beginning of the PhD. The work will consist at first in preparing the experiment with eventually some final tests of the detection system, and in the experiment itself. A large part of the thesis will then be devoted to the analysis of experimental data with existing software developed at our lab or the Institut Laue Langevin (ILL). The main goal is to better understand the influence of nuclear structure and deformation on the fission process. Experimental results will be interpreted using the de-excitation code developed at CEA Cadarache and recent models of the fission process. This project is part of a larger study of the fission process using the prompt gamma-ray emitted by the fission fragments and carried out together by our lab at IRFU, the ILL and the SPRC at CEA Cadarache. Part of the PhD thesis will be done at the research reactor of Grenoble.





Short-range correlations in exotic nuclei

SL-DRF-18-0339

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPHN)

Groupe Structure Noyau

Saclay

Contact :

Anna CORSI

Starting date : 01-10-2018

Contact :

Anna CORSI

CEA - DRF/IRFU/SPhN/Structure Noyau

01 69 08 7554

Thesis supervisor :

Anna CORSI

CEA - DRF/IRFU/SPhN/Structure Noyau

01 69 08 7554

Personal web page : http://irfu.cea.fr/Pisp/acorsi/

Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=487

The atomic nucleus is a quantum system of interacting fermions, protons and neutrons, which can be paired at short range (1 fm, much smaller than their average distance) where the nuclear interaction is poorly known and strongly repulsive. These configurations, called short-range correlations, offer us a unique opportunity to study this regime which is particularly interesting as it corresponds to the transition from a proton/neutron to quark/gluon description of the nucleus. Experiments to characterize short-range correlations have been done on stable nuclei, but the experimental technique used up to now does not allow access to unstable nuclei, where the imbalance between protons and neutrons may affect these correlations. A new technique consisting in studying short-range correlations in exotic nuclei with a proton target is under development.

The candidate will analyze data from the first test experiment that will be performed in 2018 using stable beams from the JINR accelerator in Dubna (Russia). He/she will be then strongly involved in the program proposed by the group with the radioactive beams produced by the GSI accelerator (Germany) and a liquid hydrogen target that we are currently developing thanks to a grant from the National Research Agency.

In parallel to the experimental program, he/she will perform simulations to design a new detection system based on tracking of charged particles in a magnetic field. This system will allow increased acceptance for particle identification and momentum measurement of charged particles in future experiments at GSI.

Data analysis and simulations will be performed using the C++-based ROOT and GEANT4 software, respectively, routinely employed in nuclear and subnuclear physics. The thesis will be done at CEA in close collaboration with MIT (USA) and TU Darmstadt (Germany) teams. A long stay in Darmstadt is envisaged.

From the Z boson to the Higgs boson, constraining the nunber of associated jets in the production of a boson at the LHC

SL-DRF-18-0672

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe CMS

Saclay

Contact :

Philippe Gras

Starting date : 01-10-2018

Contact :

Philippe Gras

CEA - DRF/IRFU/DEDIP

+33 1 69 08 62 81

Thesis supervisor :

Philippe Gras

CEA - DRF/IRFU/DEDIP

+33 1 69 08 62 81

Laboratory link : http://irfu.cea.fr/en

More : https://cms.cern/

We propose to distinguish the two productions mode without reconstructing jets, in the goal of reducing the measurement uncertainties coming from cross section calculation and with an expected gain of 30% on the precision of the coupling measurement. An innovative variable, N-jetiness, defined directly from the momenta of the observed particles, will be used. First, this variable will be measured in events with a Z boson and jets, produced in numbers at the LHC, and the measurement will be confronted to the cross section theoretical calculation in order to validate the incertitude reduction. This variable will then be exploited for the measurement of the Higgs boson production and of its coupling to fermions and vector bosons.

Search for beyond standard model physics in the neutrino sector at low energies

SL-DRF-18-0246

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Double Chooz

Saclay

Contact :

Matthieu Vivier

Thierry Lasserre

Starting date : 01-10-2018

Contact :

Matthieu Vivier

CEA - DRF/IRFU/SPP/

0169086626

Thesis supervisor :

Thierry Lasserre

CEA - DSM/IRFU/SPP

0169083649

Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3554

The standard model of particle physics, describing elementary particles and their interactions, is one of the most tested and successful theory of modern physics. Within this model, neutrinos are neutral and massless elementary particles, and can be of three flavors. However, the 3-flavour neutrino oscillation phenomenon, which was successfully confirmed in 1998 and 2003 by the Super Kamiokande and SNO experiments, is indisputable evidence that neutrinos are massive and hence that the standard model is incomplete. Specifically, new physics is necessary to explain how neutrinos acquire their mass, and why they are so much lighter than any other elementary particles. Many extensions of the standard model, which add massive sterile partners to the known active neutrinos, have been proposed in this sense and they can also predict the existence of new couplings for the neutrinos (namely non-standard neutrino interactions). Further to the three-flavour neutrino oscillation phenomenon, another possible evidence for physics beyond the standard model comes from the reactor antineutrino anomaly, which is a systematic deficit in the observed neutrino rate compared to expectations at various antineutrino detectors placed less than 100 m away from a nuclear reactor. This deficit could be explained by a new oscillation mode of active neutrinos toward a fourth sterile state with a mass at the eV scale.

The proposed work here consists in searching for new physics beyond the standard model in the neutrino sector at low energies. Firstly, the data collected by the CeSOX experiment will be analyzed and used to search for light sterile neutrinos. The CeSOX experiment is an international collaboration of physicists and engineers and consists in deploying an intense 144Ce radioactive source in the vicinity of the Borexino detector located at the Gran Sasso National Laboratory in Italy. The experiment will start collecting data in spring 2018, and the PhD student will be expected to participate to the data analysis effort in order to search for energy and spatial modulations of the antineutrino count rate in the detector. Such a modulation would be a smoking gun signature for the existence of a fourth neutrino state. Secondly, the PhD student will participate to evaluating the potential of a new experiment located in the vicinity of the Chooz nuclear power plant and based on the detection of coherent elastic scattering of neutrinos off nuclei, in order to probe the existence of sterile neutrinos and non-standard neutrino couplings.

Search for Dark Matter particles in finals states with two jets and a large missing transverse energy with the ATLAS detector at the LHC

SL-DRF-18-0576

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Atlas

Saclay

Contact :

Samira Hassani

Claude GUYOT

Starting date : 01-10-2018

Contact :

Samira Hassani

CEA - DRF/IRFU/SPP/Atlas

0169087226

Thesis supervisor :

Claude GUYOT

CEA - DRF/IRFU/SPP/Atlas

01 69 08 55 74

Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=1213

After the discovery of the Higgs boson at the LHC run I, one of the major forthcoming goals is the precise measurement of its couplings with the Standard Model particles in order to possibly find a hint on the existence of new particles beyond the Standard Model. This thesis will deal with the case where the Higgs boson of mass mH=125GeV decays into a pair of “invisible” particles (without interaction with the matter of the detector). Various theoretical models predict that such a particle, which couples only to the Higgs boson, could be a good candidate to form the dark matter of the Universe. At the LHC, the search for such a decay mode can be carried out, for example, through the study of the associated production VH with V (= Z or W) being a vector boson of the weak interactions or in the Higgs boson production mode called "Vector Boson Fusion" (VBF). The VH modes, with the V vector boson decaying into a quark-antiquark pair, and the VBF mode lead to final states with two energetic jets and a large missing transverse energy. We will also consider the case V = Z with the Z decaying into two charged leptons which leads to a very pure final state even in the presence of a large pile-up of proton-proton collisions per bunch crossing.

The thesis work will focus on the improvement of the analysis of these channels, which have already been performed in run1 and with the first run 2 data by the ATLAS collaboration. These improvements will proceed through the use of multivariate analysis techniques and machine learning methods (with supervised or unsupervised learning) to optimize the measurement of the missing transverse energy and the rejection of the background in the presence of a large amount of pile-up collisions and by using all the run 2 data collected at 13 TeV between 2015 and 2018.

This thesis will also include a "detector development" component with the participation in the development and testing of fast silicon sensors to equip a forward muon identification detector which should be installed in ATLAS around 2025 for the luminosity increase of the LHC.

Development of Picosec Micromegas for fast timing in high rate environments

SL-DRF-18-0579

Research field : Particle physics
Location :

Service d'Electronique, des Détecteurs et d'Informatique (DEDIP)

DÉtecteurs: PHYsique et Simulation

Saclay

Contact :

Thomas PAPAEVANGELOU

Esther FERRER RIBAS

Starting date : 01-03-2018

Contact :

Thomas PAPAEVANGELOU

CEA - DRF/IRFU/SEDI/DEPHYS

01 69 08 2648

Thesis supervisor :

Esther FERRER RIBAS

CEA - DRF/IRFU/SEDI/DEPHYS

0169083852

Personal web page : http://irfu.cea.fr/Pisp/esther.ferrer-ribas/

Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_service.php?id_unit=5

Our R&D activity on fast timing with Micromegas detectors started as an RD51 Common Fund project in

2015. The performance achieved during the first tests (see attached publication) has resulted to a grown

interest on the field within the RD51 institutes but also beyond them. Already there are teams from Greece

(Athens, Thessaloniki) and China (Hefei University) that have joined the initial collaborating groups from CEA,

CERN and Princeton. New Micromegas prototypes have been built at CERN, to add improved characteristics

to the initial CEA prototype. Furthermore, teams from Portugal and Russia are starting R&D on carbon based

photocathodes (Diamond or DLC) and secondary emitters. We plan to address numerous topics in view of the

use of the proposed concept in experiments: lifetime (of the photocathodes in particular), robustness (spark

protection), scaling to multichannel readout, large area coverage, front end electronics, high rate and so on so

forth. R&D on solid converter (photocathodes, secondary emitter) will represent clearly one of the most

important subjects of this R&D and it will necessarily involve various expertize from different fields. The PhD

student will actively participate in many of those developments. He/She will:

a) work on the development of a multi-channel prototype (few tens of strips or pads).

One of the tasks proposed in this thesis is to build such a multichannel detector, (about 5x5cm2), and have it

tested for mid-2018 before the writing of the Technical Design Report by the ATLAS collaboration foreseen for

end 2018. The first step on this R&D will be to study the effect of the fragmentation of the anode and the

implied charge sharing on the performance of the detector. In the first stage the anode will be non-resistive in

order to directly compare with the existing data and isolate the effect of the fragmentation. The first prototype

will have pads arranged in a honeycomb geometry and its size will be limited to ~5 cm. The number of the

readout channels will be ~10. The fabrication is planned for June 2018, in collaboration with CERN. A

new chamber and PCB board with strips will be designed and built during the 2nd half of 2018 at SEDI. A

version with resistive strips is also planned, having active area of ~5x5 cm2.

b) participate in the development of diamond based photocathodes with sufficient photoelectron yield and

investigate diamond based secondary emitter as an alternative.

The development will be carried out at the CEA/DRT/List/DM2I/LCD laboratory, under the supervision of

Michal Pomorski. The Diamond Sensors Laboratory counts 20 researchers and holds ten years of expertise in

diamond materials: from thin diamond films synthesis to modifications of diamond nanoparticles. The team is

one of the largest and best known groups in France in diamond research.

We plan to develop: i) Boron-doped Nanocrystalline Thin Diamond Films (BNCD) as Photocathode. Ii)

Diamond Nanoparticles (ND) Decorated Surfaces as Photocathode. iii) Thick Diamond Films as Secondary

Emitter investigating also commercially available diamond films. The PhD student will have to get familiar with

the use of some of the facilities and will follow the sample production. His main task however will be the study

of the performance of the samples, as it is described in the item c) bellow.

c) establish a platform to measure the photocathode quantum efficiency (QE)and study the timing

performance of the prototype at the IRAMIS fs UV laser and at the RD51 test beam facilities at CERN.

The QE of a photocathode under study can be estimated relatively to a known photocathode using a cosmic

ray telescope and two identical detectors, operating under the same conditions. Absolute measurements can

be performed with the use of a UV spectrometer. The student will be responsible for the establishment of the

setup and will use it to characterize the photocathodes. Another setup using a powerful continuous UV lamp

will be needed to study the aging properties of the photocathode. The most performing photocathodes will be

used for the measurements with charged particle test beams at CERN and at the IRAMIS femtosecond UV

laser.





Modeling of reactor antineutrino spectra

SL-DRF-18-0251

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Double Chooz

Saclay

Contact :

Matthieu Vivier

Starting date : 01-10-2018

Contact :

Matthieu Vivier

CEA - DRF/IRFU/SPP/

0169086626

Thesis supervisor :

Matthieu Vivier

CEA - DRF/IRFU/SPP/

0169086626

Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=424

Since their discovery in 1956, reactor antineutrinos played an important role in unveiling and understanding the fundamental properties of the neutrino. Neutrinos are elementary particles which come in three flavors, each associated to the electron, muon, and tau particles. When propagating, neutrinos can especially change from one flavor to another, a phenomenon known as neutrino flavor oscillation. Nuclear power plants are copious sources of antineutrinos, and are therefore interesting to precisely measure the neutrino oscillation probability with one or several dedicated detectors placed nearby.

Reactor antineutrinos originate from minus beta decay of the products initiated by the fission of nuclear fuel (U235, U238, Pu239, Pu241). The resulting antineutrino spectrum is therefore a superposition of thousands of beta branches. In 2011, the reactor neutrino group at CEA/Irfu reassessed the state of the art predictions of reactor antineutrino flux calculations for the Double Chooz experiment, located at the Chooz nuclear power plant in northern France. Since then, this new reactor antineutrino flux modeling has been extensively used by experiments using reactor antineutrinos, such as Double Chooz. However, the latest experimental reactor antineutrinos spectra, as for example measured by the Daya Bay and Double Chooz experiments, turned out to be surprisingly different from the current predictions. To explain the disagreement between theory and experimental results, the scientific community agrees on the fact that several assumptions made for predicting antineutrino reactor fluxes are imprecise or incorrect, especially those made for the modeling of a single beta branch neutrino spectrum.

The goal of the following PhD thesis is to revise and refine the calculations of the reactor antineutrino spectra with regards to the modeling of the single beta branch spectra making a reactor antineutrino spectrum. This work will be carried out within the team of the NENuFAR (New Evaluation of Neutrino Fluxes At Reactors) project, which is supported and funded by the transversal program direction of the CEA. To do so, the successful candidate will have to develop optimized calculation tools to precisely model any single beta branch spectrum, by including all known electromagnetic and atomic corrections to the V-A theory of beta decay and a correct treatment of the forbidden transitions. The impact of such refinements to the reactor antineutrino spectrum modeling will then be studied to address the current disagreement between experience and theory. Also, these new calculations should be extended to the low energy domain (E<1.8 MeV) for which no reliable calculations yet exist.

Search for the Higgs boson decaying in 2 photons and produced in association with top quarks in the CMS experiment.

SL-DRF-18-0279

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe CMS

Saclay

Contact :

Julie Malcles

Starting date : 01-10-2018

Contact :

Julie Malcles

CEA - DRF/IRFU/SPP/CMS

+33 1 69 08 86 83

Thesis supervisor :

Julie Malcles

CEA - DRF/IRFU/SPP/CMS

+33 1 69 08 86 83

Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=1424

More : https://cms.cern/

The ATLAS and CMS experiments at the LHC at CERN discovered in 2012 a new boson compatible with the Higgs boson predicted by the Standard Model of particle physics. The determination of its properties is now one of the main goals in experimental particle physics at LHC. A measurement of the Higgs production in association with a pair of top quarks (ttH) would allow to access to the Higgs Yukawa coupling to the top quark, a fundamental parameter of the Standard Model (SM) of particle physics. The top quark being the most massive particle, this coupling could play a special role in the electroweak symmetry breaking mecanism. This is thus one of the most interesting measurement to be conducted at LHC nowadays. The ttH production is a very rare process, two orders of magnitude smaller than the dominant Higgs boson production by gluon fusion, its measurement is thus challenging. A sensitivity of about 3 standard deviations could be obtained in the diphoton channel with the 150 inverse femtobarn expected to be available by the end of 2018. A very first observation of the ttH production could also be obtained during this thesis by combining several Higgs boson decay channels. This is thus the perfect moment to work on this production mode. The IRFU CMS group has a great expertise in photon energy measurement and was one of the leading groups in all CMS Higgs to two photons analysis at 13 TeV, specifically for the study of the ttH production in this channel. The student will greatly benefit from group’s knowledge to lead these studies.

Study of Deeply Virtual Compton Scattering at COMPASS at CERN

SL-DRF-18-0282

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPHN)

Groupe COMPASS

Saclay

Contact :

Nicole d'Hose

Starting date : 01-10-2018

Contact :

Nicole d'Hose

CEA - DRF/IRFU/SPhN

01 69 08 72 72

Thesis supervisor :

Nicole d'Hose

CEA - DRF/IRFU/SPhN

01 69 08 72 72

Laboratory link : http://irfu.cea.fr/Sphn/Phocea/Vie_des_labos/Ast/ast_sstheme.php?id_ast=32

More : http://wwwcompass.cern.ch/compass/gpd/index.html

For the last few years hadronic physicists have been measuring exclusive reactions such as Deeply Virtual Compton Scattering to determine the Generalized Parton Distributions of the nucleon. This will give the best description of the internal structure of the nucleon to further understand the collective organization of its partonic constituents, quarks and gluons, governed by the strong interaction. In particular, Parton Distribution Functions (PDFs) studied in Deeply Inelastic Scattering describe the structure of the nucleon as a function of the nucleon momentum fraction carried by a parton. PDFs have been investigated independently from nucleon electromagnetic form factors that are related to ratios of the observed elastic electron–nucleon scattering cross section to that predicted for a point-like particle. The theoretical framework of Generalized Parton Distributions (GPDs) developed at the end of the 1990s embodies both form factors and PDFs, such that GPDs can be considered as momentum-dependent form factors, which provide information on the transverse position of a parton as a function of its longitudinal momentum. Obtaining such a “3-dimensional picture” of the nucleon is sometimes referred to as “nucleon tomography”. GPDs describe the structure of the nucleon independently of the specific reaction by which the nucleon is probed, i.e. they are universal quantities. The mapping of nucleon GPDs, which is one of the key objectives of high-energy nuclear physics, requires a comprehensive program of measurements in a broad kinematic range, and various hard exclusive processes such as Deeply Virtual Compton Scattering (DVCS).

Since the late 1990s French physicists have been involved in the theoretical development and have been the principal investigators of such experiments. DVCS is the reaction lepton proton -> lepton proton photon where the lepton scattering on a proton, exchanges a virtual photon and produces only a real photon in the final state. DVCS is considered as the golden channel to study GPDs, as it interferes with the well-known Bethe-Heitler process. The goal of the experiments is to measure total cross sections and asymmetries using a variety of lepton beams of different energy, charge and polarization on polarized or unpolarized nucleons. The JLab experiment is using polarized electron beams of 12 GeV from the CEBAF accelerator. The COMPASS experiment is using positive and negative polarized muon beams of 160 GeV which are secondary beams produced at the SPS at CERN. The kinematic domains are complementary and unique at least until 2025 when a new electron proton collider can be built. Valence quarks are probed at JLab while sea quarks and gluons are revealed at COMPASS.

The proposed thesis concerns the COMPASS DVCS experiment. Two years of data taking have been performed at COMPASS in 2016 and 2017. The student will participate to the final analysis of the DVCS at COMPASS. The use of positive and negative muon beams at COMPASS allows one to measure the slight difference between the two corresponding DVCS cross sections. This will give a measurement of the DVCS amplitudes providing an access to GPDs and to the energy momentum tensor related to the quark and gluon confinement.



Determination of the pion parton distribution function in the valence region

SL-DRF-18-0694

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPHN)

Groupe COMPASS

Saclay

Contact :

Stephane PLATCHKOV

Starting date : 01-10-2018

Contact :

Stephane PLATCHKOV

CEA - DRF/IRFU/SPhN/COMPASS

0169087459

Thesis supervisor :

Stephane PLATCHKOV

CEA - DRF/IRFU/SPhN/COMPASS

0169087459

The pion is both a quark-antiquark bound state and a Nambu-Goldstone boson. This double nature – due to

confinement and symmetry breaking - has important consequences on its internal structure. Its dynamic

properties, resulting from the degrees of freedom of quarks and gluons, give the pion a unique position for

detailed studies of the strong interaction. Accessing its internal structure is therefore of upmost importance.

However, the distributions of partons in the pion are not well known. Drell-Yan is among the rare processes

allowing an access to these distributions. The extensive measurements by the COMPASS collaboration at

CERN, performed in 2015 and 2018, provide a unique opportunity for a determination of the pion PDF in the

valence region.

The proposed PhD thesis has experimental and phenomenological parts. The experimental part includes data

analysis, Monte-Carlo simulation of the apparatus and determination of final cross-sections. The phenomenological

part comprises the extraction of the distribution of the valence quarks in the pion and an extensive comparison

with the available theoretical calculations

Stusy of the Higgs boson couplings in its decay to two Z gauge bosons with the ATLAS detector data at the LHC

SL-DRF-18-0310

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Atlas

Saclay

Contact :

Claude GUYOT

RODANTHI NIKOLAIDOU

Starting date : 01-10-2018

Contact :

Claude GUYOT

CEA - DRF/IRFU/SPP/Atlas

01 69 08 55 74

Thesis supervisor :

RODANTHI NIKOLAIDOU

CEA - DRF/IRFU/SPP/Atlas

0169086157

Laboratory link : http://irfu.cea.fr/Spp/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=3424

The main part of the thesis will consist of an analysis of the run-2 data (taken between 2015 and 2018 at 13 TeV in the proton-proton center of mass system) for the study of the Higgs boson nature. The project consists in measuring the couplings of the Higgs boson via its decay into 4 leptons (electrons or muons) resulting from the decay of two Z-gauge bosons, in a regime where we move away from its mass shell (the invariant mass of 4 leptons is superior to the mass of the Higgs boson, the so-called "off-shell" regime), to be finally combined with the corresponding results obtained from the "on-shell" coupling measurements (at the Higgs mass). In practice, our task will be to measure the cross section of the pp-> ZZ-> 41 process over a wide range of the invariant mass of the 4 final state leptons. This ZZ decay channel offers the best sensitivity due to its clean signature with excellent signal-to-background ratio. New interactions beyond the standard model would affect both the rate and the differential distributions of the final 4-lepton state. The comparison between the on-shell and off-shell production cross-sections thus makes it possible to put an upper limit on the total width of the Higgs boson via the quantum interference effects between the different production modes of ZZ pairs at high invariant mass. This total width would be directly affected by non-standard couplings to certain particles of the standard model or by the presence of decay channels to new particles beyond the standard model.

The analysis will be carried out by classifying the events in relation to the number of jets produced in association with the system of 4 leptons (ZZ + n-jets) to distinguish between the different modes of production of the Higgs boson.



A second part of this thesis will be dedicated to the understanding, analysis and exploitation of MicroMegas type gas detectors. Sensors of this type will replace part of the ATLAS muon spectrometer and be operational for the restart of the LHC in 2021.

The IRFU is one of the construction sites of this type of detector. The student will participate in the functional tests of the modules once they arrive at CERN after their construction in Saclay.

Reactor neutrino anomaly : Stereo experiment analysis

SL-DRF-18-0231

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPHN)

Groupe MNM

Saclay

Contact :

Alain Letourneau

Starting date : 01-10-2018

Contact :

Alain Letourneau

CEA - DSM/IRFU/SPhN/LEARN

33 (0)1 69 08 76 01

Thesis supervisor :

Alain Letourneau

CEA - DSM/IRFU/SPhN/LEARN

33 (0)1 69 08 76 01

Laboratory link : http://irfu.cea.fr/Sphn/Phocea/Vie_des_labos/Ast/ast_sstheme.php?id_ast=186&id_unit=7

More : http://irfu.cea.fr/Sphn/Phocea/Vie_des_labos/Ast/ast_sstheme.php?id_ast=31

The Stereo experiment, installed closed to the ILL high-flux reactor in Grenoble, aims to detect the existence of an unpredicted by the standard model neutrino-state. This namely “sterile” state because it does not interact with electroweak interaction, could explain the reactor neutrino anomaly, i.e. a deficit of neutrinos observed in short-baseline reactor experiments.

The detector is in operation since the end of 2016, allowing to validate the functioning of the detector and to determine the level of background. Unfortunately the statistic is not sufficient and a new campaign is planned in 2018 and 2019. By the end of this campaign the statistic would be sufficient to test the hypothesis of a sterile state having a mass around 1 eV.

The thesis work will consist in participating to the measurement and to analyze the data in order to extract the anti-neutrino signal from the background. The energy distributions of the anti-neutrinos will be studied as a function of the distance to test the hypothesis of a sterile state. Regarding the result three options could be envisaged to complete the work: develop a global analysis over other new coming experiments to reduce the systematics and test the hypothesis; to improve our knowledge of the electroweak interaction in nuclei, in particular the treatment of first forbidden transitions, to explain the anomaly; to start a R&D study on a new concept of detector to increase the sensitivity and to improve the background rejection.

analysis of new observables to study the top quark and its production in association with the Higgs boson in ATLAS

SL-DRF-18-0224

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Atlas

Saclay

Contact :

Frédéric DELIOT

Starting date : 01-10-2018

Contact :

Frédéric DELIOT

CEA - DRF/IRFU/SPP

0169086628

Thesis supervisor :

Frédéric DELIOT

CEA - DRF/IRFU/SPP

0169086628

the goal of the PhD project is to study the properties of the top quark produced by pairs and in association with the Higgs boson using innovative angular variables and asymmetries in the ATLAS experiment at CERN. The quark top being the heaviest elementary particle and its coupling to the Higgs boson being the largest, its study is of primary importance to search for new phenomena beyond the Standard Model of particle physics. The first part of the PhD will be devoted to study in detail the structure of the Wtb vertex using new proposed W boson spin observables and new asymmetries. This approach is expected to enhance the sensitivity to anomalous couplings extracted from the experimental measurements.

The second part of the work will be focused on studying the CP nature of the top quark coupling to the Higgs boson in ttH events, using new angular distributions of the decay products following the same strategy as in the top-antitop case. Both of these studies will be performed in collaboration with theorists that are developing the theoretical calculation of angular distributions and asymmetries in the ttH final state with the presence of new physics.

Measurement of the Charge Parity violation in neutrino oscillations

SL-DRF-18-0234

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Neutrinos-accélérateurs

Saclay

Contact :

Sara Bolognesi

Marco ZITO

Starting date : 01-10-2018

Contact :

Sara Bolognesi

CEA - DRF/IRFU/SPP/TK2

0169081461

Thesis supervisor :

Marco ZITO

CEA - DRF/IRFU/SPP/TK2

0169083819

Personal web page : http://personalpages.to.infn.it/~bolognes/work.html

Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=2032

More : http://t2k-experiment.org/

The discovery of neutrino oscillations has demonstrated that neutrinos have mass, which cannot be explained in the framework of the Standard Model. Neutrino physics is therefore today a very promising sector to look for New Physics.

The T2K (Tokai to Kamioka) experiment in Japan is studying neutrino oscillations exploiting a beam of muon neutrinos. The beam is produced by the J-PARC accelerator in Tokai, it passes through the near detector at 280 m from the production point and it heads to the far detector Super-Kamiokande, placed at a distance of 295 km. The neutrino oscillations are measured by observing the differences in the neutrino flux and flavor at the near and far detectors. In particular, the comparison of neutrino and anti-neutrino oscillations allows to measure a fundamental parameter still unknown: the phase which parametrizes the violation of CP in the oscillation. The measurement of such parameter allows the first observation of CP violation in the leptonic sector which could play a fundamental role in the explication of matter-antimatter asymmetry in the Universe. T2K data have today constrained for the first time the value of the phase excluding the CP conservation with a confidence level of 90%. Much larger statistics is needed for a more precise measurement and the T2K collaboration is planning a new data taking period (T2K-2) with higher beam power until 2026.

The student will work on the oscillation analysis with the present T2K data and in view of the increase in statistics expected in the next years, including T2K-2. The work will focus on the improvement of the systematic uncertainties, in particular due to the modelling of neutrino-nucleus interactions. The student will also work on improving the oscillation analysis to minimize the impact of such uncertainties, for instance including in the analysis new variables describing the kinematics of the outgoing hadrons produced in the interactions (pions and nucleons).

Study of distorsion induced by space charge and ion backflow to optimize a TPC aimed at measuring the Higgs boson properties at future e+/e- experiments

SL-DRF-18-0608

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe ILC

Saclay

Contact :

Boris TUCHMING

Starting date : 01-10-2018

Contact :

Boris TUCHMING

CEA - DRF/IRFU/SPP/ILC

01 69 08 97 78

Thesis supervisor :

Boris TUCHMING

CEA - DRF/IRFU/SPP/ILC

01 69 08 97 78

Personal web page : http://irfu.cea.fr/Pisp/boris.tuchming/

More : http://irfu.cea.fr/Phocea/file.php?class=pisp&reload=1490104150&file=boris.tuchming/files/123/canavas_presentation_FCC_TPC_v1.pdf

Next generation of high energy e+e- colliders (linear or circular) will be dedicated to study finely the properties of the Higgs bosons and search for new physics beyond de standard model. The future e+e- detectors require tracking systems of unequalled stability and precision. An attractive detection technique for charge particles is the Time Projection Chamber (TPC). Charged particles leave an ionization trail of electron-ion pairs in the gazeous volume. The electrons from the primary ionization drift under the combined effect of a magnetic and electric field to the end flanges of the detector where they are amplified by avalanche effect. An important issue, is the mastering of the back flow of positive ions into the drift volume, where they induce a space charge and distortions on primary electron trajectories. We propose to study experimentally the distortions, arising from positive ions, using a test bench based on a TPC prototype of medium size (100 liters) at Saclay, using Micromegas techniques for the detection part and an UV lamp to create space charge. The work will consists in running the test bench and the data acquisition system to analyze the data and reconstruct tracks from cosmic muons. The performance as a function the space charge will be compared to simulations. The goal is to optimize the future tracking system in view of precise measurement of the Higgs boson mass, of the W boson mass, or of the Yukawa coupling of the Higgs boson to the muons.

Towards a high spatial resolution pixel detector for particle identification: new detectors contribution to physics

SL-DRF-18-0701

Research field : Particle physics
Location :

Service d'Electronique, des Détecteurs et d'Informatique (DEDIP)

DÉtecteurs: PHYsique et Simulation

Saclay

Contact :

Nicolas FOURCHES

Paul COLAS

Starting date : 01-09-2018

Contact :

Nicolas FOURCHES

CEA - DRF/IRFU/SEDI/DEPHYS

0169086164

Thesis supervisor :

Paul COLAS

CEA - DSM/IRFU/SPP/ILC

0169086155

More : https://doi.org/10.1109/TED.2017.2670681

Future experiments on linear colliders (e+e-) 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 positionned closest to the interaction point.This will provide the opportunity to make precision lifetime measurements of short lived charged particles such as b-quarks (b-tagging) and taus. The search for extra-dimensions would benefit from such a detector.The technologies that are necessary to implement such detectors need to be further studied and within a limited amount of time should lead to a small prototype on which the main characteristics may be evaluated. Such technologies (TRAMOS, DOTPIX) are on the verge of giving a significant advance in vertexing and the efforts in this directions should be pursued. These technologies follow the trend of monolithic integration of the detector with the readout electronics. The fields of physics that these detectors open up should be reviewed and developed. These detectors open up the possibility for direct detection of short lived particles. These detectors should be implemented on the future e+e- collider,that have low hadronic background.

Determination of the weak mixing angle with the 13 TeV data recorded by Atlas at the LHC

SL-DRF-18-0319

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Atlas

Saclay

Contact :

Nathalie Besson

Starting date : 01-10-2018

Contact :

Nathalie Besson

CEA - DRF/IRFU/SPP/Atlas

0169088274

Thesis supervisor :

Nathalie Besson

CEA - DRF/IRFU/SPP/Atlas

0169088274

The entire particle content of the Standard Model (SM) of particle physics is now established experimentally. Accurate measurements of the masses and couplings of the most massive known particles, the W, Z and Higgs bosons and the top-quark, further test the SM, verifying whether the measured values of these parameters follow the predicted relations. Improvements in the weak mixing angle measurement would strongly benefit to these precision tests.

With the LHC as sole high-energy collider in operation, future measurements of the electroweak parameters will be strongly affected by uncertainties stemming from the structure of the proton beam particles. These uncertainties already dominate the existing

hadron-collider weak-mixing angle determinations. This common source of uncertainty also generates significant correlations among the electroweak parameter measurements. If not treated properly, these uncertainties and corrélations can compromise the validity of future electroweak consistency tests.

The solution proposed here consists in organizing a joint determination of the electroweak mixing angle and the proton parton densities, exploiting the lepton angular distributions in Z boson decays. This measurement will include a dedicated study of the ATLAS Inner Detector alignment, a measurement of the decay asymmetry as a function of invariant mass and rapidity, the extraction of the weak mixing angle using Z boson data recorded at 13 TeV by Atlas, and using this result together with the ATLAS results on the W boson mass, the high mass Drell-Yann and the Higgs boson, a global interpretation allowing to constrain new physics models.

Accretion-ejection coupling in microquasars

SL-DRF-18-0658

Research field : Particle physics
Location :

Service d'Astrophysique (DAP)

Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)

Saclay

Contact :

Jérôme RODRIGUEZ

Stéphane CORBEL

Starting date : 01-09-2018

Contact :

Jérôme RODRIGUEZ

CEA - DRF/IRFU/SAp/LEPCHE

01 69 08 98 08

Thesis supervisor :

Stéphane CORBEL

Université Paris 7 - DRF/IRFU/SAP/LEPCHE

01 69 08 45 62

Development of an innovative muon tomography instrument for societal applications

SL-DRF-18-0288

Research field : Particle physics
Location :

Service d'Electronique, des Détecteurs et d'Informatique (DEDIP)

DÉtecteurs: PHYsique et Simulation

Saclay

Contact :

David Attié

Sébastien Procureur

Starting date : 01-10-2018

Contact :

David Attié

CEA - DRF/IRFU/SEDI/DEPHYS

(+33)(0)1 69 08 11 14

Thesis supervisor :

Sébastien Procureur

CEA - DRF/IRFU/SPhN/CLAS

(+33)(0)1 69 08 39 22

More : https://www.nature.com/articles/nature24647

Muon tomography, or muography, consists in using cosmic muons to perform deep imaging of structures. These highly energetic muons, produced in showers generating from the interaction of cosmic rays with the atmosphere, can indeed cross several hundred meters of stones before being absorbed. The outstanding progress achieved in the last years on particle detectors (spatial resolution, robustness, electronics, etc.) have recently elicited a high interest for muography in many different fields.



A first muon telescope prototype was built and tested in 2015, using Micro-Pattern Gaseous Detectors (Micromegas) with a patented multiplexing scheme. The next year, three new telescopes were deployed around the Khufu's pyramid in Egypt, showing their robustness in extreme conditions (temperature, dust, etc.). Their detection of the "ScanPyramids Big Void" in combination with Japanese instruments located inside the pyramid are a world premiere for outdoors instruments.



These developments triggered the interest of many industrials and researchers for this technology. But like an optical telescope, muon telescopes are quite directional and still not very compact. An elegant solution consists in using a Time Projection Chamber (TPC), which allows for a full trajectory reconstruction with better precision and in a quasi-isotropical way.



The goal of this PhD is then to design, build and test in real conditions such an instrument. One of the main key points concerns the TPC autonomy, in particular the gas consumption, but also its overall stability in outside conditions. A sealed or semi-sealed TPC with a gas purification system, easily transportable and resistant to environmental variations would be a major breakthrough in muon tomography and for gaseous detectors in general.



Through this project, the PhD student will have the opportunity to cover a large spectrum of activities (design, integration, detector characterization, electronics, data analysis, simulation, etc.) and will then acquire skills in multiple aspects of experimental physics. The small size of the team (~6 people) will also ensure a great visibility to his/her work.

Design and construction of Micromegas detectors for the sPHENIX experiment at the Brookhaven National Laboratory and simulations of jet reconstruction in the sPHENIX Time Projection Chamber

SL-DRF-18-0321

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPHN)

Groupe ALICE

Saclay

Contact :

Hugo PEREIRA DA COSTA

Starting date : 01-09-2018

Contact :

Hugo PEREIRA DA COSTA

CEA - DRF/IRFU/SPhN/ALICE

+33 169087308

Thesis supervisor :

Hugo PEREIRA DA COSTA

CEA - DRF/IRFU/SPhN/ALICE

+33 169087308

Quantum Chromodynamics (QCD) is the theory of quark and gluons. Lattice QCD calculations predict that above a certain critical temperature Tc a phase transition occurs between normal nuclear matter for which quarks and gluons are confined inside hadrons and a Quark-Gluon Plasma (QGP) in which they are deconfined. In central Gold-on-Gold collisions such as those delivered at the Relativistic Heavy Ion Collider (RHIC) at the Brookhaven National Laboratory (BNL) in the United States, a QGP is believed to be formed at a characteristic temperature of order 1 to 2 Tc. In this regime, the quarks and

gluons constituting the QGP have been found to be interacting strongly, despite being deconfined, which led to the introduction of the term sQGP whose properties are not unlike that of a perfect fluid.



sPHENIX is an experiment being build at RHIC as a replacement of the now decommissioned PHENIX experiment. It aims at pinning down the properties of the sQGP in a regime complementary to that which is being studied at the LHC by the ALICE, ATLAS and CMS. Its apparatus combines precise charged particle reconstruction and identification using a state of the art Time Projection Chamber (TPC) together with calorimetry both hadronic and electromagnetic, targeting full jet reconstruction. sPHENIX design and construction has started in 2017. It is expected to take data in 2023. In the meanwhile

many challenges have to be met regarding both detectors and software for the experiment to achieve its foreseen performances.



The proposed PhD thesis subject consists in designing and building Micromegas detectors to equip the sPHENIX TPC. The detectors must provide a good enough spacial resolution in order to measure the momentum of the charged particles produced during the Gold-Gold collisions with high accuracy. At the same time, it must be designed in a way that will

minimize the presence of positive charges (ions) in the TPC volume. These charges, if too numerous and for the high collision rates foreseen at RHIC, could create local distortions to the electric field in the TPC and ruin its ability to properly reconstruct the particle's trajectory.



Micromegas detectors are parallel plate gas detectors that consist of two stages: (i) a drift stage that coincides with the TPC drift volume and (ii) an amplification stage delimited by the printed circuit board responsible for collecting the signal and a mesh. The electric field in the amplification stage is very large, resulting in an avalanche process when entered by an electron coming from the drift stage. The positive ions resulting from this avalanche are the ones that could cause electric field distortions in the TPC. Part of the student's job during his/her PhD will be to study the possibility to add one or several extra meshes on top of the amplification mesh in order to capture these ions before they enter the drift volume. This will require the design and characterization of smaller size detector prototypes, as well as simulations of space charge distributions in these prototypes.



In addition, the student will also work on simulations of the sPHENIX detector and in particular on how tracking and particle identification is performed in the TPC in presence of possible electric field distortions due to the remaining ions. While working on such simulations the student will also examine the capabilities of the sPHENIX detector

for measuring physics observables such as jet sub-structure, heavy flavor tagged jets or bottomonium production, in the presence of the QGP.



Our group at the Department of Nuclear Physics (DPhN) in CEA/Saclay has a well established expertise in heavy ion physics and the study of the QGP. It has made significant contributions to both PHENIX at RHIC and ALICE at the LHC. Its growing involvement into sPHENIX is the natural continuation of these activities. In parallel, the Department of Electronics, Detectors and Computing for Physics (DEDIP) is the leading authority in matters of Micromegas detector design, construction and operation. The student will work in a rich environment constituted of both physicist and engineers coming from these two departments. He/She will have to show interest in both detector hardware and simulations,

either analysis or physics oriented.

Observation and measurements of the Higgs boson produced in association with a top-antitop pair in the ATLAS experiment

SL-DRF-18-0303

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Atlas

Saclay

Contact :

Frédéric DELIOT

Henri BACHACOU

Starting date : 01-10-2018

Contact :

Frédéric DELIOT

CEA - DRF/IRFU/SPP

0169086628

Thesis supervisor :

Henri BACHACOU

CEA - DRF/IRFU/SPP/Atlas

+41227675650

Laboratory link : irfu.cea.fr/Spp

More : http://atlas.cern.ch/

With the discovery of a new boson compatible with the Standard Model (SM) Higgs boson, a new era of particle physics has begun. One of the most important topics in particle physics for the incoming years is to study the nature of the Higgs boson and its connection with possible extensions of the SM, such as Supersymmetry or Extra-dimension theories. It is especially interesting to understand the relationship of the Higgs boson with the heaviest elementary particle, the top quark, and to measure the Yukawa coupling between the top quark and the Higgs boson. The only process which has a direct sensitivity to the top-quark Yukawa coupling is the production of a Higgs boson (H) in association with a top-anti-top pair (ttbar). This channel is one of the most challenging ones to be measured at LHC.



After two years of shut-down, the LHC has restarted in 2015 with higher instantaneous luminosities and a higher center of mass energy of 13 TeV. It is expected to deliver an integrated luminosity of more than 120 fb-1 by the end of 2018. With this amount data, the ATLAS experiment is expected to be able to observe the ttbar-H process and measure its production cross-section. The PhD candidate will be expected to take an important role in this new measurement.



Given the small expected ttH cross section, it is important to focus on the channel with the largest Higgs branching ratio. With a mass of 125 GeV, the more abundant Higgs decay channel is into a pair of b quarks. However ttH with H into b-bbar is one of the most challenging channels at the LHC because of the large background from tt+jets. Discovering the ttH channel will require an excellent understanding of the SM background and of the detector performance. The focus will particularly be on the reconstruction of the ttH final state and on the modelling of the ttbar+jets background.

Control Doping of superconducting radio frequency cavities for future accelerators

SL-DRF-18-0536

Research field : Solid state physics, surfaces and interfaces
Location :

Service des Accélérateurs, de Cryogénie et de Magnétisme (DACM)

Laboratoire d’Intégration et Développement des Cavités et Cryomodules (LIDC2)

Saclay

Contact :

thomas proslier

Claire ANTOINE

Starting date : 01-09-2018

Contact :

thomas proslier

CEA - DRF/IRFU/SACM/LIDC2

0169088711

Thesis supervisor :

Claire ANTOINE

CEA - DSM/IRFU/SACM/LIDC2

+33 169 08 73 28

Laboratory link : http://irfu-i.cea.fr/Sacm/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=3301&voir=theme

Superconducting RF (SRF) cavities, made of pure niobium, are the corner stone infrastructure of most actual and future particle accelerators and one of the largest operational and constructional challenge. The performances of SRF cavities are determined by the interactions, under an external RF magnetic field, between the superconducting properties and defects present within a surface layer of a few penetration depth, ?, ~50 nm. As performances increase, the in-depth understanding of the correlations between the performances and materials characteristics becomes more stringent, down to the nm scale, pushing for new characterisation methods and a higher level of process control.

This thesis aims at studying the effects of a controlled dopant incorporation on the superconducting surface electronic, structural and chemical properties and to find correlations between these properties and the RF performances. The goal of this thesis is to push Nb SRF cavities performances well beyond what is currently achievable. The student will be trained to use state of the art surface characterisation tools, among which the tunneling spectroscopy in particular, as well as be exposed to various doping methods (gases, solid film etc..). Among the 3 years of this project, the selected candidate will gain significant knowledge in condensed matter physics and superconductivity in particular, and some particle accelerator physics. This thesis with a strong experimental component, will also include some theoretical effort within existing collaborations.

 

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