19 sujets IRFU/DPhP

Dernière mise à jour :


• Accelerators physics

• Astroparticles

• Astrophysics

• Mathematics - Numerical analysis - Simulation

• Particle physics

 

Optimisation of the Gbar experiment for the production of antihydrogen ions

SL-DRF-24-0746

Research field : Accelerators physics
Location :

Service de Physique des Particules (DPHP)

Groupe Antimatière et gravitation (GAG)

Saclay

Contact :

Boris TUCHMING

Starting date : 01-10-2024

Contact :

Boris TUCHMING
CEA - DRF/IRFU

0169089778

Thesis supervisor :

Boris TUCHMING
CEA - DRF/IRFU

0169089778

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

Laboratory link : https://irfu.cea.fr/dphp/Phocea/Vie_des_labos/Ast/ast.php?t=fait_marquant&id_ast=5149

The aim of the Gbar experiment (Gravitational Behavior of Antihydrogen at Rest) at CERN is to produce a large number of antihydrogen atoms to measure their acceleration in Earth's gravitational field. The principle relies on the production of antihydrogen ions through two successive charge exchange reactions that occur when a beam of antiprotons passes through a positronium cloud. In 2022, Gbar demonstrated its operational scheme by producing antihydrogen atoms through the first charge exchange reaction. The current focus is on optimizing and improving various elements of the experiment to achieve the production of anti-H+, particularly the positron line leading to the creation of the positronium cloud. The challenge is to increase the number of positrons trapped in the second electromagnetic trap of the line, and then to transport them efficiently to the reaction chamber where they are converted into positronium.
The thesis work will involve operating, diagnosing, and optimizing the two electromagnetic traps of the line, as well as the positron acceleration and focusing devices to yield a sufficient number of positroniums and then the production of antihydrogen ions. The student will also participate in the measurement campaign for studying the mater counterpart of the second charge exchange reaction, relying upon a beam of H- ion instead of the beam of antiprotons.
First observations of the TeV gamma-ray sky with the NectarCAM camera for the CTA observatory

SL-DRF-24-0435

Research field : Astroparticles
Location :

Service de Physique des Particules (DPHP)

Groupe Astroparticules (GAP)

Saclay

Contact :

Francois BRUN

Jean-François Glicenstein

Starting date : 01-10-2024

Contact :

Francois BRUN
CEA - DRF/IRFU


Thesis supervisor :

Jean-François Glicenstein
CEA - DRF/IRFU/DPHP/HESS 2

0169089814

Laboratory link : https://irfu.cea.fr/dphp/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=3429&voir=technique

Very high energy gamma-ray astronomy is a relatively young part of astronomy (30 years), looking at the sky above 50 GeV. After the success of the H.E.S.S. array in the 2000s, an international observatory, the Cherenkov Telescope Array (CTA), should start operating by 2025. This observatory will include a total of 50 telescopes, distributed on two sites. IRFU is involved in the construction of the NectarCAM, a camera intended to equip the "medium" telescopes (MST) of CTA. The first NectarCAM (of the nine planned) is being integrated at IRFU and will be installed on the North site of CTA in 2025. Once the camera is installed, the first astronomical observations will take place, allowing to fully validate the functioning of the camera. The thesis aims at finalizing the darkroom tests at IRFU, preparing the installation and validating the operation of the camera on the CTA site with the first astronomical observations. It is also planned for the student to participate in H.E.S.S. data analysis on astroparticle topics (search for primordial black holes, constraints on Lorentz Invariance using distant AGN).
High-energy transient astrophysical phenomena

SL-DRF-24-0498

Research field : Astroparticles
Location :

Service de Physique des Particules (DPHP)

Groupe Astroparticules (GAP)

Saclay

Contact :

Fabian Schussler

Starting date : 01-10-2024

Contact :

Fabian Schussler
CEA - DRF/IRFU

+33169083020

Thesis supervisor :

Fabian Schussler
CEA - DRF/IRFU

+33169083020

Personal web page : https://www.multimessenger-astronomy.com/

Laboratory link : https://irfu.cea.fr/dphp/index.php

The core of the proposed thesis project will be the real-time search for transient high-energy emission linked to the detection of a gravitational waves and other multi-messenger astrophysical transients like high-energy neutrinos, gamma-ray bursts, fast radio bursts, stellar/nova explosions, etc. The combined observations across multiple instruments and cosmic messengers will unequivocally prove the existence of a high-energy particle accelerators related to these phenomena and will allow to derive novel insights into the most violent explosions in the universe.
Joining the H.E.S.S., CTA and SVOM collaborations the PhD candidate will be able to lead the exciting MWL and multi-messenger campaigns collected during the physics run O4 of the GW interferometers, the first high-energy neutrino events detected by KM3NeT and the first GRBs detected by the SVOM satellite. The PhD candidate will also have the opportunity to participate in the development of the Astro-COLIBRI platform allowing to follow transient phenomena in real-time via smartphone applications.
STUDY OF THE GALACTIC CENTER AND DIFFUSE EMISSION SEARCHES IN VERY-HIGH-ENERGY GAMMA RAYS WITH H.E.S.S. AND PROSPECTS WITH CTA

SL-DRF-24-0578

Research field : Astroparticles
Location :

Service de Physique des Particules (DPHP)

Groupe Astroparticules (GAP)

Saclay

Contact :

Emmanuel MOULIN

Starting date : 01-10-2023

Contact :

Emmanuel MOULIN
CEA - DRF/IRFU//GAP

01 69 08 29 60

Thesis supervisor :

Emmanuel MOULIN
CEA - DRF/IRFU//GAP

01 69 08 29 60

Very-high-energy (E>100 GeV) gamma-ray observations of astrophysical objects are a crucial tool for the understanding of the most violent non-thermal acceleration processes taking place in the Universe. The gamma rays allow to attack fundamental questions across a broad range of topics, including supermassive black holes, the origin of cosmic rays, and searches for new
physics beyond the Standard Model. Multi-wavelength observations of the center of the Milky Way unveil a complex and active region with the acceleration of cosmic rays to TeV energies
and beyond in astrophysical objects such as the supermassive black hole Sagittarius A* lying at the center of the Galaxy, supernova remnants or star-forming regions. The Galactic Centre (GC) stands out as one of the most studied regions of the sky in nearly every wavelength, and has been the target of some of the deepest exposures with high-energy observatories. Beyond the diversity of astrophysical accelerators, the GC should be the brightest source of dark matter particle annihilations in gamma rays.
The GC region harbors a cosmic Pevatron, i.e., a cosmic-ray particle accelerator to PeV energies, diffuse emissions from GeV to TeV such as the Galactic Centre Excess (GCE) whose origin is still unknown, potential variable TeV sources as well as likely unresolved source population. The interaction of electrons accelerated in these objects produces very-high-energy gamma rays
via the inverse Compton process of electrons scattering off ambient radiation fields. These gamma rays can also be efficiently produced through decays of neutral pions from inelastic
collisions protons and nuclei with the ambient gas. Among possible unresolved source populations in the GC region are millisecond pulsars in the Galactic bulge or an intermediate-mass (~20-10^5 Msun) black holes following the dark matter distribution of the Galactic halo. About 10^3 sources would be needed to explain the GCE emission. Such source population would leave characteristic imprints in the background fluctuations for which surveys of the GC region in TeV gamma rays with the H.E.S.S. observatory and the forthcoming CTA are unique to scrutinize them.
The H.E.S.S. observatory composed of five atmospheric Cherenkov telescopes detects gamma rays from a few ten GeV up to several ten TeV. H.E.S.S. has carried out extensive observations
of the GC with recently an observational campaign of the inner several degrees around the GC. The dataset accumulated so far provides an unprecedented sensitivity to study the acceleration and propagation of TeV cosmic rays and search for dark matter signals in the most promising region of the sky. These observations are unique to shape the observation programs of the future observatory CTA, optimize their implementation, and prepare future analyses.
The PhD thesis project will be focused on the analysis and interpretation of the observations carried out in the GC region by the H.E.S.S. over about 20 years. The first part of the work will be devoted to the low-level analysis of the GC data, the study of the systematic uncertainties in this massive GC dataset and the development of dedicated background models. In the second part, the PhD student will combine all the GC observations in order to search for TeV diffuse emissions, unresolved population of sources, and dark matter signals using multi-template analysis techniques including background modelling approaches. The third part will be dedicated to the implementation of the new analysis framework to CTA forthcoming data to prepare future GC analyses using the most up-to-date signal and background templates. In addition, the PhD student will be involved in the data taking and data quality selection of H.E.S.S. observations.
Data analysis and fundamental physics with LISA and Pulsar Timing Array

SL-DRF-24-0288

Research field : Astrophysics
Location :

Service de Physique des Particules (DPHP)

Groupe Astroparticules (GAP)

Saclay

Contact :

Marc Besancon

Antoine PETITEAU

Starting date : 01-10-2024

Contact :

Marc Besancon
CEA - DSM/IRFU/SPP


Thesis supervisor :

Antoine PETITEAU
CEA - DRF/IRFU


There are two types of instruments to observe gravitational waves (GW) at low frequency: space-based interferometer in the milliHertz (mHz) band, and Pulsar Timing Array (PTA) in the nanoHertz (nHz) band. They are complementary either by observing two parts of the same sources as for stochastic backgrounds or two parts of the same population of sources as for massive black hole binaries.
LISA is space-based GWs observatory which is planned for launch in 2035. It consists of three satellites in the free fall in the heliocentric orbit forming an equilateral triangle. Satellites exchange laser light forming multiple interferometers allowing to observe a plethora of astrophysical and cosmological sources of GWs. These sources include galactic white dwarf binaries, extreme mass-ratio inspirals, massive black hole binaries, stochastic backgrounds.
PTA is using the timing of millisecond pulsars to observe GWs. Millisecond pulsars emit about hundreds of radio pulses per second with very high regularity. GWs passing between pulsar and Earth, modifies the time of arrival of the pulses. The timing an array of pulsars, enable to make a galactic scale GW detector. Multiple radio-telescopes contribute to PTA, in particular the Nançay Radio-Telescope. In June 2023, 4 PTA collaborations announced the results of 20 years of pulsar timing: strong evidence for a GWs signal. The signal still needs to be characterized and its origin established. It could have been emitted by an ensemble of super-massive black holes or by processes in the primordial Universe. While the two observing systems are different, the data analysis methods are similar. A large parameter space needs to be sampled to extract overlapping sources and disentangle them from the non-stationary noises.
GWs are a new way to learn about fundamental physics. For example, we can test general relativity with the merger of super-massive black holes binary and Extreme Mass ratio Inspiral and test particle physics beyond the standard model, thanks to the detection of stochastic background (SGWB) from phase transitions in the early Universe. The candidate will work at the CEA-IRFU (Institut de Recherche sur les Lois Fondamentales de l'Univers) as part of a cross-disciplinary team conducting research into GWs. This activity ranges from instrumental involvement in the LISA mission to the astrophysical or cosmological consequences of exploiting the signals, via the development of algorithms, simulations and data analysis. IRFU is also involved in PTA-France and International PTA. Developing methods for detecting gravitational wave sources and deducing the associated physical consequences is at the heart of the proposed thesis topic. The candidate will have the opportunity to take an interest in all aspects of the host team's activity and to interact with each of its members. The main objectives of the proposed work are to develop data analysis methods for LISA, taking advantage of developments in PTA and LISA, and to study the synergy between LISA and PTA observations for fundamental physics, in particular with SGWBs and Massive Black Holes (MBHs). The methods developed can also be adapted and applied to real PTA data. The candidate will be a member of the collaborations LISA, PTA-France, EPTA and IPTA. He/she will interact with members of the Groupement de Recherche Ondes Gravitationnelles and collaborate with physicists from the Astroparticles et Cosmologie (APC) laboratory. He will present his results within the LISA and PTA consortiums and at international conferences.
Studying inflation with quasars and galaxies in DESI

SL-DRF-24-0627

Research field : Astrophysics
Location :

Service de Physique des Particules (DPHP)

Groupe Cosmologie (GCOSMO)

Saclay

Contact :

Etienne Burtin

Christophe YECHE

Starting date : 01-10-2024

Contact :

Etienne Burtin
CEA - DRF/IRFU/DPHP/GCOSMO

01 69 08 53 58

Thesis supervisor :

Christophe YECHE
CEA - DRF/IRFU/SPP/Bao

01-69-08-70-50

Measurements of the statistical properties of the large-scale structure (LSS) of the universe provide information on the physics that generated the primordial density fluctuations. In particular, they enable us to distinguish between different models of cosmic inflation by measuring primordial non-Gaussianity (PNG), the deviation from the initial conditions of the Gaussian random field.

Our strategy for studying LLS is to use a spectroscopic survey, DESI, whose instrument was commissioned at the end of 2019. DESI will observe 40 million galaxies and quasars. Observations take place at the 4-m Mayall telescope in Arizona. In the spring of 2021, the project began a five-year period of uninterrupted observations, covering a quarter of the sky.

For this thesis project, LSS are measured with two tracers of matter: very luminous red galaxies (LRG) and quasars, very distant and very luminous objects. These two tracers enable us to cover a wide redshift range from 0.4 to 4.0.

During the first year of his/her thesis, the student will contribute to the final analysis of the first year of DESI observations. In particular, he/she will study LSS with quasars and galaxies (LRG). His/her work will also involve assessing all possible sources of bias in the selection of quasars and LRGs that could contaminate a cosmological signal. In a second phase, the student will develop a more sophisticated analysis using three-point statistics such as the bispectrum with an extended sample to the first three years of DESI observations.
Detecting the first clusters of galaxies in the Universe in the maps of the cosmic microwave background

SL-DRF-24-0595

Research field : Astrophysics
Location :

Service de Physique des Particules (DPHP)

Groupe Cosmologie Millimétique

Saclay

Contact :

Jean-Baptiste Melin

Starting date : 01-09-2024

Contact :

Jean-Baptiste Melin
CEA - DRF/IRFU/DPHP/Cosmo mm

01 69 08 73 80

Thesis supervisor :

Jean-Baptiste Melin
CEA - DRF/IRFU/DPHP/Cosmo mm

01 69 08 73 80

Laboratory link : https://irfu.cea.fr

Galaxy clusters, located at the node of the cosmic web, are the largest gravitationally bound structures in the Universe. Their abundance and spatial distribution are very sensitive to cosmological parameters, such the matter density in the Universe. Galaxy clusters thus constitute a powerful cosmological probe. They have proven to be an efficient probe in the last years (Planck, South Pole Telescope, XXL, etc.) and they are expected to make great progress in the coming years (Euclid, Vera Rubin Observatory, Simons Observatory, CMB- S4, etc.).
The cosmological power of galaxy clusters increases with the size of the redshift range covered by the catalogue. The attached figure shows the redshift ranges covered by the catalogues of galaxy clusters extracted from experiments observing the cosmic microwave background (first light emitted in the Universe 380,000 years after the Big Bag). One can see that Planck detected the most massive clusters in the Universe in the redshift range 0 Only the experiments studying the cosmic microwave background will be able to observe the hot gas in these first clusters at 2 One thus needs to understand and model the emission of the gas as a function of redshift, but also the emission of radio and infrared galaxies inside the clusters to be ready to detect the first clusters in the Universe. Irfu/DPhP developed the first tools for detecting clusters of galaxies in cosmic microwave background data in the 2000s. These tools have been used successfully on Planck data and on ground-based data, such as the data from the SPT experiment. They are efficient at detecting clusters of galaxies whose emission is dominated by the gas, but their performance is unknown when the emission from radio and infrared galaxies is significant.
This thesis will first study and model the radio and infrared emission from galaxies in the clusters detected in the cosmic microwave background data (Planck, SPT and ACT) as a function of redshift.
Secondly, one will quantify the impact of these emissions on existing cluster detection tools, in the redshift range currently being probed (0 Finally, based on our knowledge of these radio and infrared emissions from galaxies in clusters, we will develop a new cluster extraction tool for high redshift clusters (2
GAMMA INTERACTION RECONSTRUCTION IN CLEARMIND PET DETECTOR USING HIGH-EFFICIENT AI ALGORITHM

SL-DRF-24-0265

Research field : Mathematics - Numerical analysis - Simulation
Location :

Service de Physique des Particules (DPHP)

Groupe Santé et Energie (GSE)

Saclay

Contact :

Viatcheslav SHARYY

Dominique YVON

Starting date : 01-10-2024

Contact :

Viatcheslav SHARYY
CEA - DRF/IRFU

0169086129

Thesis supervisor :

Dominique YVON
CEA - DRF/IRFU

01 6908 3625

Personal web page : https://irfu.cea.fr/Pisp/viatcheslav.sharyy

Laboratory link : https://irfu.cea.fr/en/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3937

Positron emission tomography (PET) is a medical nuclear imaging technique widely used in oncology and neurobiology. The decay of the radioactive tracer emits positrons, which annihilate into two back-to-back photons of 511 keV. These pairs of photons are detected in coincidence and used to reconstruct the distribution of the tracer activity in the patient's body.
In this thesis, we propose to contribute to the development of the cutting-edge patented technology ClearMind. The first prototype is currently being tested in the laboratory. The proposed detector uses a monolithic lead tungsten crystal in which Cherenkov and scintillation photons are produced. Those photons are converted to electrons by the photo-electric layer and multiplied in a microchannel plate. The induced electrical signals are amplified by gigahertz amplifiers and digitized by the fast acquisition modules SAMPIC. The opposite surface of the crystal will be equipped with a matrix of the silicon photo-multiplier. Machine-learning techniques will be applied for processing the complex acquired signals in order to reconstruct the time and coordinates of the gamma-conversion in the crystal.

The candidate will work on the development of high-efficient machine learning algorithm for the reconstruction of the gamma-conversion vertex in the monolithic crystal. In particular, this work consists in the evolution and improvement of the existing Geant4 detector simulation for its adjustment to the prototype performances as measured in the laboratory. This simulation will provide a training dataset for the development and optimization of deep neural networks with a focus on reconstructing vertex parameters and estimation of the uncertainties on these parameters (i.e., robust IA).
Calibrations on multiple detectors will prepare several batches of realistic performance test data, allowing us to assess the stability of our methods across domain changes. These data inherently contain noise and will thus also serve as rigorous tests of robustness.
These algorithms will enable the efficient reconstruction of gamma interactions using either the full signal shape and/or pre-processed data (feature engineering). Special attention will be given to developing compact, efficient, and fast networks. The possibility of embedding these algorithms in FPGA for real-time reconstruction may also be explored.
ADVANCED ARTIFICIAL INTELLIGENCE TECHNIQUES FOR PARTICLE RECONSTRUCTION IN THE CMS DETECTOR USING PRECISION TIMING AND ATTENTION MECHANISM

SL-DRF-24-0448

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe CMS (CMS)

Saclay

Contact :

Mehmet Ozgur SAHIN

Fabrice COUDERC

Starting date : 01-10-2024

Contact :

Mehmet Ozgur SAHIN
CEA - DRF/IRFU/DEDIP/STREAM

01 69 08 14 67

Thesis supervisor :

Fabrice COUDERC
CEA - DRF/IRFU/DPHP

01 69 08 86 83

Laboratory link : https://irfu.cea.fr/en/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=2292

Particle reconstruction in collider detectors is a multidimensional problem where machine learning algorithms offer the potential for significant improvements over traditional techniques. In the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC), photons and electrons produced by the collisions at the interaction point are recorded by the CMS Electromagnetic Calorimeter (ECAL). The large number of collisions, coupled with the detector's complex geometry, make the reconstruction of clusters in the calorimeter a formidable challenge. Traditional algorithms struggle to distinguish between overlapping clusters created by proximate particles. In contrast, It has been shown that graph neural networks offer significant advantages, providing better differentiation between overlapping clusters without being negatively affected by the sparse topology of the events. However, it is crucial to understand which extracted features contribute to this superior performance and what kind of physics information they contain. This understanding is particularly important for testing the robustness of the algorithms under different operating conditions and for preventing any biases the network may introduce due to the difference between data and simulated samples (used to train the network).
In this project, we propose to use Gradient-weighted Class Activation Mapping (Grad-CAM) and its attention mechanism aware derivatives to interpret the algorithm's decisions. By evaluating the extracted features, we aim to derive analytical relationships that can be used to modify existing lightweight traditional algorithms.
Furthermore, with the upcoming High Luminosity upgrade of the LHC, events involving overlapping clusters are expected to become even more frequent, thereby increasing the need for advanced deep learning techniques. Additionally, precision timing information of the order of 30 ps will be made available to aid in particle reconstruction. In this PhD project, we also aim to explore deep learning techniques that utilize Graph and Attention mechanisms (Graph Attention Networks) to resolve spatially proximate clusters using timing information. We will integrate position and energy deposition data from the ECAL with precision timing measurements from both the ECAL and the new MIP Timing Detector (MTD). Ultimately, the developed techniques will be tested in the analysis of a Higgs boson decaying into two beyond-the-standard-model scalar particles.

We are seeking an enthusiastic PhD candidate who holds an MSc degree in particle physics and is eager to explore cutting-edge artificial intelligence techniques. The selected candidate will also work on the upgrade of the CMS detector for the high-luminosity LHC.
Study of the production of pairs of Higgs bosons in the bbtt decay channel

SL-DRF-24-0377

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe CMS (CMS)

Saclay

Contact :

Louis Portales

Julie Malcles

Starting date : 01-10-2024

Contact :

Louis Portales
CEA - DRF/IRFU/DPHP/CMS

+33 1 69 08 86 83

Thesis supervisor :

Julie Malcles
CEA - DRF/IRFU/DPHP/CMS

+33 1 69 08 86 83

The CMS group at CEA-Saclay/IRFU/DPhP proposes a thesis on the search for double Higgs boson production in the decay channel with a pair of bottom quarks and a pair of tau leptons. The study of this production gives a direct access to the Higgs boson self-coupling, parameter still to be measured. The selected student will take part to research activities well established within CMS, within the CEA group, in link with other institutes in France and abroad. He or she will have to develop an analysis using the Run 3 data of LHC, and in particular to optimise the trigger strategy with regard to previous such analyses. Several publications are foreseen: a first one using the data collected in 2022 and 2023, combined with Run 2 if the sensitivity gain is as large as expected, and a second one using the full Run 2 and Run 3 data. A contribution to the combination of HH results in the different sensitive channels is also foreseen. In parallel, the student will be able to also take part in activities related to detector upgrades, in particular in calorimetry, benefiting from the great expertise of the group in this domain.
Optimization of gamma radiation detectors for medical imaging. Time-of-flight positron emission tomography

SL-DRF-24-0263

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Santé et Energie (GSE)

Saclay

Contact :

Dominique YVON

Viatcheslav SHARYY

Starting date : 01-09-2024

Contact :

Dominique YVON
CEA - DRF/IRFU

01 6908 3625

Thesis supervisor :

Viatcheslav SHARYY
CEA - DRF/IRFU

0169086129

Personal web page : https://irfu.cea.fr/Pisp/dominique.yvon/

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

Positron emission tomography (PET) is a nuclear medical imaging technique widely used in oncology and neurobiology. The decay of the radioactive tracer emits positrons, which annihilate into two photons of 511 keV. These photons are detected in coincidence and used to reconstruct the distribution of tracer activity in the patient's body.
We are offering you the opportunity to contribute to the development of an ambitious, patented technology: ClearMind.
You will work in an advanced instrumentation laboratory in a particle physics environment.
Your first task will be to optimize the "components" of ClearMind detectors, in order to achieve nominal performance.
We'll be working on scintillating crystals, optical interfaces, photo-electric layers and associated fast photo-detectors, readout electronics.
We will then characterize the performance of the prototype detectors on our measurement benches, which are under continuous development. The data acquired will be interpreted using in-house analysis software written in C++ and/or Python.
Finally, the physics of our detectors will be modeled using Monté-Carlo simulation (Geant4/Gate software), and we will compare our simulations with our results on measurement benches. A special effort will be devoted to the development of ultra-fast scintillating crystals in the context of a European collaboration.
Search for Higgs boson production with a single top and study of the CP properties of the top-Higgs coupling in the diphoton channel with the CMS experiment at the LHC.

SL-DRF-24-0623

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe CMS (CMS)

Saclay

Contact :

Julie Malcles

Starting date : 01-03-2024

Contact :

Julie Malcles
CEA - DRF/IRFU/DPHP/CMS

+33 1 69 08 86 83

Thesis supervisor :

Julie Malcles
CEA - DRF/IRFU/DPHP/CMS

+33 1 69 08 86 83

Ten years ago, the ATLAS and CMS experiments at LHC at CERN discovered a new boson, with a dataset of proton-proton collisions of about 10 fb-1 at the centre of mass energy of 7 to 8 TeV [1,2]. Since then, the properties of this particle have been tested by both experiments and are compatible with the Higgs boson properties predicted by the Standard Model of particle physics (SM) within the uncertainties. In absence of direct probes of New Physics, increasing the accuracy of the measurements of the properties of the Higgs boson (its spin, its parity and its couplings to other particles) remains one of the most promising path to pursue.
The measurement of the ttH production allows the direct access to the top quark Yukawa coupling, fundamental parameter of the SM. ttH production is a rare process, two orders of magnitude smaller than the dominant Higgs boson production by gluon fusion. This production mode has been observed for the first time in 2018 [3, 4] separately by the CMS and ATLAS experiments, by combining several decay channels. More recently, with the full Run 2 dataset (data recorded between 2016 and 2018, with a total of 138 fb-1 at 13 TeV), this production mode was observed also using solely the diphoton decay channel, and a first measurement of its CP properties was provided again by both experiments, with the exclusion of a pure CP odd state at 3s [5, 6]. The associated production with a single top quark is about 5 times smaller than the ttH production and has never been observed. Thanks to the searches in the diphoton and multilepton channel, very loose constraints on this production modes were set for the first time recently (see Ref. [7]). This production mode is very sensitive to the H-tt coupling CP properties, since in case of CP-odd coupling, its production rate is largely increased. We propose in this thesis to study jointly the two production modes (ttH and tH) and the H-tt coupling CP properties with Run 3 data (data being recorded now and until 2026, with potentially about 250 fb-1 at 13.6 TeV) in the diphoton decay channel. If there was some CP violation in the Higgs sector, excluding small pseudo-scalar contributions will require more data. Pursuing these studies with Run 3 and beyond may allow to pinpoint small deviations not yet at reach. We propose to bring several improvements to the Run 2 analysis strategy and to use novel reconstruction and analysis techniques based on deep-learning, developped in the CEA-Saclay group by our current PhD students but not yet used in physics analyses, in order to make the most of the available dataset.
[1] ATLAS Collaboration, “Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC,” Phys. Lett. B 716 (2012) 1.
[2] CMS Collaboration, “Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC,” Phys. Lett. B 716 (2012) 30.
[3] ATLAS Collaboration, “Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector”, Phys. Lett. B 784 (2018) 173.
[4] CMS Collaboration, “Observation of ttH Production”, Phys. Rev. Lett. 120 (2018) 231801.
[5] CMS Collaboration, “Measurements of ttH Production and the CP Structure of the Yukawa Inter- action between the Higgs Boson and Top Quark in the Diphoton Decay Channel”, Phys. Rev. Lett. 125, 061801.
[6] ATLAS Collaboration, “CP Properties of Higgs Boson Interactions with Top Quarks in the ttH and tH Processes Using H ? ?? with the ATLAS Detector” , Phys. Rev. Lett. 125 (2020) 061802.
[7] CMS Collaboration, “A portrait of the Higgs boson by the CMS experiment ten years after the discovery”, Nature 607 (2022) 60.
Neutrino oscillation at T2K: the road to Charge-Parity violation discovery

SL-DRF-24-0387

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Neutrinos Accélérateurs (GNA)

Saclay

Contact :

Sara Bolognesi

Starting date : 01-10-2024

Contact :

Sara Bolognesi
CEA - DRF/IRFU/SPP/TK2

0169081461

Thesis supervisor :

Sara Bolognesi
CEA - DRF/IRFU/SPP/TK2

0169081461

Why is the observable Universe today made of matter, without any significant amount of antimatter? Neutrinos shed light on this cosmic mystery.
In 2020, the T2K collaboration in Japan published in the journal Nature [1] new results leading to the best constraint to date on the parameter dCP, which translates in the theory the degree of asymmetry between matter and antimatter. The T2K results exclude for the first time nearly half of the possible values at 99.7% (3s) and the value most compatible with the data is very close to -90° corresponding to a maximum asymmetry between matter and antimatter. T2K has the best world sensitivity for this fundamental parameter and is going to collect new data from 2023 with an upgraded detector to search for a possible discovery of symmetry violation.
T2K is a neutrino experiment designed to study the transition of neutrinos from one flavor to another as they travel (neutrino oscillations). An intense beam of muon neutrinos is generated at the J-PARC site on the east coast of Japan and directed to the SuperKamiokande neutrino detector in the mountains of western Japan. The beam is measured once before leaving the J-PARC site, using the ND280 near-field detector, and again at SuperKamiokande: the evolution of the measured intensity and the composition of the beam are used to determine the properties of the neutrinos.
The thesis work will focus on the analysis of the data for the measurement of the neutrino oscillations with new upgraded near detector installed in 2023. The objective of this new detector is to improve the performance of the ND280 near detector, to measure the neutrino interaction rate and to constrain the neutrino interaction cross sections so that the uncertainty on the number of events predicted at SuperKamiokande is reduced to about 4% (from about 8% today). The upgrade of the near detector will require to put in place a new analysis strategy to enable precise measurement of the neutrino oscillations. For the first time, the measurement of low momentum protons and neutrons produced by neutrino interactions will be exploited. Another important part of the analysis which must be updated to cope with increased statistics, is the modeling of the flux of neutrinos produced by the accelerator beamline.
A new generation of experiments is expected to multiply the data production in the next decades. In Japan, the Hyper-K experiment, and in the USA, the DUNE experiment, will be operational around 2027-2028. This thesis work will explore new analysis strategies crucial also for such next-generation experiments. If their new data confirm the preliminary results of T2K, neutrinos could well bring before ten years a key to understand the mystery of the disappearance of antimatter in our Universe.
The natural width of the Higgs boson in the diphoton channel

SL-DRF-24-0374

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe CMS (CMS)

Saclay

Contact :

Fabrice COUDERC

Starting date : 01-10-2023

Contact :

Fabrice COUDERC
CEA - DRF/IRFU/DPHP

01 69 08 86 83

Thesis supervisor :

Fabrice COUDERC
CEA - DRF/IRFU/DPHP

01 69 08 86 83

Laboratory link : https://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=3425

More : https://cms.cern

The Higgs boson discovered at the LHC in 2012 is the cornerstone of the Standard Model (SM). Its properties, such as its mass or spin, are now better and better known. Nevertheless, the total width of the Higgs boson remains a fundamental parameter that is very difficult to measure at the LHC without the support of theoretical assumptions.
In this PhD thesis, we propose to pursue an original approach to measure this parameter, approach only possible in the diphoton decay channel of the Higgs boson. Indeed, in this channel the position of the mass peak depends on the interference between the Higgs boson signal and the background noise. The resulting shift depends on the natural width of the Higgs boson. This is a very small effect in the SM but could be larger when considering Higgs bosons produced at high transverse momentum.
This type of analysis requires a thorough mastery of the various uncertainties related to the experimental apparatus, in particular to the electromagnetic calorimeter (ECAL), and to the reconstruction of the electromagnetic objects. In order to improve the latter, the student will develop a new approach to electromagnetic-object reconstruction based on a technique initiated at CEA-Irfu by the CMS group and using state-of-the-art methods in artificial intelligence (Convolutional NN and Graph NN).
These two aspects will be addressed in parallel during the thesis. The student will be supervised by the CMS group of Irfu whose expertise in the ECAL and in the two-photon Higgs boson decay channel is internationally recognised.
Construction of a Micromegas tracker for the P2 experiment, and measurement of the electroweak mixing angle in electron-proton scattering

SL-DRF-24-0428

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Atlas (ATLAS)

Saclay

Contact :

Maarten Boonekamp

Maxence Vandenbroucke

Starting date : 01-09-2024

Contact :

Maarten Boonekamp
CEA - DRF/IRFU/SPP/Atlas

0169085990

Thesis supervisor :

Maxence Vandenbroucke
CEA - DRF/IRFU/DEDIP

01 69 08 22 83

This thesis project concerns the precise measurement of the electroweak mixing angle with the P2 experiment, at the MESA accelerator, in Mainz. The measurement will make it possible to test, for the first time, the prediction of the Standard Model for the evolution of this fundamental parameter as a function of the energy scale, and the effects of possible new particles or interactions.

The determination of the mixing angle is based on a precise measurement of the variation of the scattering cross section of an electron beam on a liquid hydrogen target, as a function of the polarization of the beam. This asymmetry, measured in scattering at forward angles, is affected by significant systematic uncertainties linked to the structure of the proton. A measurement of the scattering asymmetry in the backward direction, using a dedicated detector, makes it possible to reduce these uncertainties, and constitutes the subject of this thesis.

The thesis project arrives at a crucial moment in the development of the experiment, and will allow the student to participate directly in the construction of a very high performance detector, its installation in the P2 experiment, and its scientific exploitation.

Development of cryogenic detectors with particle identification for double beta decay searches

SL-DRF-24-0243

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Sources et Réacteurs (GNSR)

Saclay

Contact :

Claudia Nones

Starting date : 01-11-2024

Contact :

Claudia Nones
CEA - DRF

0169083520

Thesis supervisor :

Claudia Nones
CEA - DRF

0169083520

Neutrinoless double beta decay (0n2b) is a theoretical nuclear transition, whose observation would become a major milestone in particle, and in particular, neutrino physics. This process, if it exists, violates lepton number conservation law and confirms Majorana nature of neutrino. The detection of 0n2b is a challenging task, since it is a very rare decay (T1/2>10^26 years), and the experiments require high detection efficiency, energy resolution, radiopurity, large mass and very low background levels. Several ton-scale experiments are in preparation, but in paralell, new approaches have to be investigated for higher sensitivity levels. The TINY project proposes new detection technology, based on cryogenic detectors (measured at mK temperatures). The thesis subject will be mainly dedicated to the development of new thermal sensors, Zr- and Nd-containing detectors characterization, performance evaluation and evaluation of technology applicability for a ton-scale experiment. The student will develop skills on operation of cryogenic facility, signal processing, data analysis and simulations. Finally, a demonstrator will be prepared with the goal to set new limits on 0n2b for 96-Zr and 150-Nd, and perform precision measurements of 2n2b decay.
First detection of coherent elastic neutrino nucleus scattering at a reactor with the NUCLEUS experiment

SL-DRF-24-0320

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Sources et Réacteurs (GNSR)

Saclay

Contact :

Matthieu Vivier

Thierry Lasserre

Starting date : 01-10-2024

Contact :

Matthieu Vivier
CEA - DRF/IRFU/DPHP/Double Chooz

0169086626

Thesis supervisor :

Thierry Lasserre
CEA - Liste des pôles/Liste des départements/Liste des services/Double Chooz

0169083649

This PhD topic is about the NUCLEUS experiment, which aims to accurately measure the process of coherent elastic neutrino scattering on nuclei (CEvNS) at the Chooz nuclear power plant in the French Ardennes. Although at ~MeV energies, CEvNS is the dominant interaction process of neutrinos with matter, it has remained unobserved for a very long time because of the difficulty of measuring the weak nuclear recoils it induces. It was only 40 years after its first prediction that this process was observed for the first time with neutrinos of a few tens of MeV at the Oak Ridge laboratory accelerator facility. The first detection of CEvNS at a nuclear reactor remains to be achieved, especially because the corresponding nuclear recoils lie in an energy regime (~100 eV) which is difficult to measure with conventional detection technologies, and also because of the unfavorable background conditions nuclear power plant environments generally offer. The NUCLEUS collaboration is therefore working on the design of an innovative detection system using two cryogenic calorimeter arrays (CaWO4 & Al2O3) capable of reaching ~10 eV energy thresholds, and surrounded by a twofold system of instrumented cryogenic vetoes. This set of cryogenic detectors will be protected by an external passive shielding and by a muon veto to improve the identification and discrimination of backgrounds. With this system, NUCLEUS aims at a precise measurement of CEvNS in order to push the study of the fundamental properties of the neutrino as well as the search for beyond standard model physics towards the low energy frontier. Interestingly, CEvNS also exhibits a cross-section 10 to 1000 times larger than the usual ~MeV neutrino detection channels (inverse beta decay reaction, neutrino-electron scattering process), making it possible to miniaturize future long-range neutrino detection setups.

The experiment is currently in its initial commissioning and testing phase at the Technical University of Munich (TUM). This step will be followed in 2024 by several data acquisition runs, aiming at (i) qualifying and validating the performances of the various detectors, (ii) validating the overall background reduction strategy, and (iii) studying and mitigating the "excess", an exponential increase in the count rate of low-energy events observed in the cryogenic calorimeters, which are of unknown origin and could degrade the experiment's sensitivity to a CEvNS signal. The relocation of the experiment to the Chooz nuclear power plant will be led by our team and will take place after the summer 2024. It is in this context that the student will begin his/her PhD work, contributing to all of the integration and commissioning operations. This crucial step will require a serie of various tests and data acquisitions to set up, fine-tune and synchronize the experiment's various detection systems. She/he will focus in particular on the external cryogenic veto and on the muon veto systems, both designed and built by our team. The analysis and the exploitation of data from this on-site commissioning phase at Chooz will enable the student to get acquainted with all existing low- and high-level analysis tools for diagnosing and characterizing these detectors. One of the student's tasks will be to improve these tools, and to set up an automation chain for diagnosing and processing the large volume of daily data (~10 TB) that will be taken during the experiment's first physics run.
Extracting the CEvNS signal from data requires several preliminary studies. The first one is to characterize the energy and time response of the detectors over the data acquisition periods. The student will take charge of one of these tasks, building on the work already accomplished during the commissioning phase. This work will lead to a detailed understanding of the operation of the detectors and the identification of all the factors likely to influence their behavior. It should be noted that our team has proposed and is responsible for an innovative method for the calibration of very low energy nuclear recoils in cryogenic calorimeters, with the installation of a dedicated facility on a low-power research reactor located at the Technical University of Vienna (Austria). The student may eventually get involved in this effort, with a view to interpreting the data collected at Chooz. Building on these results, the student will then focus on the extraction and the study of a specific background component in the collected data. This work will enable the consolidation and the fine-tuning of a predictive model of the experiment's background, using a Monte Carlo simulation framework based on the Geant 4 library. Finally, the student will set up simple statistical tests to characterize the level of confidence with which a CEvNS signal can be extracted from the data after subtraction of the measured backgrounds.
Finally, the student will use the first data from the physics run at Chooz to conduct a search for new physics beyond the standard model (measurement of the weak mixing angle at low energies, search for new neutrino couplings, constraints on the electromagnetic properties of the neutrino, etc.). This work will require the implementation of advanced statistical methods for interpreting the data, in order on the one hand to understand the impact of the various sources of uncertainty on the obtained constraints, and on the other hand to guarantee the reliability of the results.
Testing the Standard Model in the Higgs-top sector in the multilepton final using the ATLAS detector at the LHC

SL-DRF-24-0577

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Atlas (ATLAS)

Saclay

Contact :

Frédéric DELIOT

Starting date : 01-10-2024

Contact :

Frédéric DELIOT
CEA - DRF/IRFU

0169086424

Thesis supervisor :

Frédéric DELIOT
CEA - DRF/IRFU

0169086424

The thesis proposes to measure in a coherent way the different rare processes of production of top quarks in association with bosons in the final state with multiple leptons at the Large Hadron Collider (LHC). The thesis will be based on the analysis of the large dataset collected and being collected by the ATLAS experiment at a record energy. The joint analysis of the ttW, ttZ, ttH and 4top processes, where one signal process becomes background when studying the other ones, will allow to get complete and unbiased measurements of the final state with multiple leptons.
These rare processes, which became accessible only recently at the LHC, are powerful probes to search for new physics beyond the Standard Model of particle physics, for which the top quark is a promising tool, in particular using effective field theory. Discovering signs of new physics that go beyond the limitations of the Standard Model is a fundamental question in particle physics today.
Alignment of the muon spectrometer and measurement of the electroweak mixing angle at the TeV scale

SL-DRF-24-0046

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Atlas (ATLAS)

Saclay

Contact :

Maarten Boonekamp

Starting date : 01-01-2024

Contact :

Maarten Boonekamp
CEA - DRF/IRFU/SPP/Atlas

0169085990

Thesis supervisor :

Maarten Boonekamp
CEA - DRF/IRFU/SPP/Atlas

0169085990

This thesis project concerns the precise measurement of the electroweak mixing angle with the ATLAS experiment, at the LHC. The evolution with energy of this fundamental parameter will also be tested. The measurement will be based on the di-muon data set from runs 2 and 3 of the LHC, and will use the muon spectrometer as the main instrument.

The determination of the mixing angle is based on the measurement of the forward-backward asymmetry of the Z boson decay muons. For precise control of systematic uncertainties, the internal alignment of the spectrometer must be optimized. This alignment constitutes an important part of the project. The performance of the New Small Wheel, the new muon detector installed for run 3, will also need to be understood in detail. The actual measurement will be carried out at the end of these preliminary studies, and an interpretation of the result will complete the thesis.

 

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