58 sujets IRFU

Dernière mise à jour :


• Accelerators physics

• Artificial intelligence & Data intelligence

• Astroparticles

• Astrophysics

• Mathematics - Numerical analysis - Simulation

• Nuclear Physics

• Nuclear physics

• Particle physics

• Various

 

Caliste-3D CZT: development of a miniature, monolithic and hybrid gamma-ray imaging spectrometer with improved efficiency in the 100 keV to 1 MeV range and optimised for detection of the Compton effect and sub-pixel localisation

SL-DRF-24-0838

Location :

Département d’Electronique, des Détecteurs et d’Informatique pour la physique (DEDIP)

LAboratoire des SYstèmes de Détection

Saclay

Contact :

Rémy Le Breton

Aline Meuris

Starting date : 01-09-2024

Contact :

Rémy Le Breton
CEA - DRF/IRFU


Thesis supervisor :

Aline Meuris
CEA - DRF/IRFU/DAP/LSAS

01 69 08 12 73

Multi-wavelength observation of astrophysical sources is the key to a global understanding of the physical processes involved. Due to instrumental constraints, the spectral band from 0.1 to 1 MeV is the one that suffers most from insufficient detection sensitivity in existing observatories. This band allows us to observe the deepest and most distant active galactic nuclei, to better understand the formation and evolution of galaxies on cosmological scales. It reveals the processes of nucleosynthesis of the heavy elements in our Universe and the origin of the cosmic rays that are omnipresent in the Universe. The intrinsic difficulty of detection in this spectral range lies in the absorption of these very energetic photons after multiple interactions in the material. This requires good detection efficiency, but also good localisation of all the interactions in order to deduce the direction and energy of the incident photon. These detection challenges are the same for other applications with a strong societal and environmental impact, such as the dismantling of nuclear facilities, air quality monitoring and radiotherapy dosimetry.

The aim of this instrumentation thesis is to develop a versatile '3D' detector that can be used in the fields of astrophysics and nuclear physics, with improved detection efficiency in the 100 keV to 1 MeV range and Compton events, as well as the possibility of locating interactions in the detector at better than pixel size.

Several groups around the world, including our own, have developed hard X-ray imaging spectrometers based on high-density pixelated semiconductors for astrophysics (CZT for NuSTAR, CdTe for Solar Orbiter and Hitomi), for synchrotron (Hexitec UK, RAL) or for industrial applications (Timepix, ADVACAM). However, their energy range remains limited to around 200 keV (except for Timepix) due to the thinness of the crystals and their intrinsic operating limitations. To extend the energy range beyond MeV, thicker crystals with good charge carrier transport properties are needed. This is currently possible with CZT, but several challenges need to be overcome.

The first challenge was the ability of manufacturers to produce thick homogeneous CZT crystals. Advances in this field over the last 20 years mean that we can now foresee detectors up to at least 10 mm thick (Redlen, Kromek).

The main remaining technical challenge is the precise estimation of the charge generated by the interaction of a photon in the semiconductor. In a pixelated detector where only the X and Y coordinates of the interaction are recorded, increasing the thickness of the crystal degrades spectral performance. Obtaining Z interaction depth information in a monolithic crystal theoretically makes it possible overcome the associated challenge. This requires the deployment of experimental methods, physical simulations, the design of readout microelectronics circuits and original data analysis methods. In addition, the ability to localise interactions in the detector to better than the size of a pixel will help to solve this challenge.
Early disk formation and the onset of universal star-formation, a probe of the influence of dark baryons

SL-DRF-24-0444

Location :

Direction d’Astrophysique (DAP)

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

Saclay

Contact :

David ELBAZ

Starting date : 01-10-2024

Contact :

David ELBAZ
CEA - DRF/IRFU/DAP/LCEG

0169085439

Thesis supervisor :

David ELBAZ
CEA - DRF/IRFU/DAP/LCEG

0169085439

The James Webb Space Telescope has revealed the presence of spiral galaxies very early in the history of the universe (up to redshifts greater than z=5). The appearance of disks so early on is surprising, as they are fragile structures, and seems to reinforce the idea that angular momentum is contributed by the accretion of intergalactic matter. This phenomenon of accretion through cooled filaments could explain several unexpected results from the James Webb. It could also be at the origin of the universal star formation, known as secular star formation, observed in galaxies in the form of a correlation between star formation rate and stellar mass (main sequence of star formation, MS). They would provide the reservoirs for star formation and help regulate it. This represents a major paradigm shift in our understanding of the origin of galaxy shapes and their star formation history. During this thesis, we will address this question through the access to data from the James Webb, Euclid and numerical models to test this hypothesis. It should be noted that without this type of explanation for the high efficiency of galaxy formation observed by the James Webb, we would have to invoke much more drastic changes that could open up a new field. This thesis will help to determine this.
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.
Design and manufacturing of a 4D-emittancemeter for characterization of very high current ion sources

SL-DRF-24-0034

Research field : Accelerators physics
Location :

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

Laboratoire d’Ingénierie de Systèmes Accélérateurs et Hyperfréquences (LISAH)

Saclay

Contact :

Olivier TUSKE

Maxence Vandenbroucke

Starting date : 01-10-2024

Contact :

Olivier TUSKE
CEA - DRF/IRFU/SACM/LEDA

+33 1 69 08 68 20

Thesis supervisor :

Maxence Vandenbroucke
CEA - DRF/IRFU/DEDIP

01 69 08 22 83

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

More : https://irfu.cea.fr/dedip/index.php

Ion accelerators, including protons, at very high intensity (> 50 mA), find numerous applications in various fields of nuclear physics or material characterization for medical, nuclear, and other applications. The Department of Accelerators, Cryogenics, and Magnetism (DACM) at CEA-Saclay specializes in the design and realization of very high-intensity ion sources.
With the increase in beam current, these sources become increasingly complex. Therefore, mastering the quality of the beam becomes critical to limit power deposition and the activation of accelerator elements. To better understand and describe this beam, it is necessary to determine its 4D emittance, which includes both the geometric shape of the beam and its trajectory. The device used for this measurement is called a 4D emittance meter.
Such a device based on a scintillator has already been designed and tested. This scintillator converts a portion of the beam into an image, which is then captured by a camera. Unfortunately, while this technology is functional at high energy, it is not suitable at the source outlet, at low energy, as the scintillation layers are quickly damaged by the ion flux.
The charge reading method proposed in this thesis is novel and benefits from the synergy between particle detector research for high-energy physics and proton source research. Instead of using a camera for reading, the idea is to measure, from a PCB placed directly in the beam, the current carried by the ions. This method allows reading this current at several thousand positions to obtain the 4D emittance. The fast acquisition system will also allow observing the temporal variation of the emittance during the start-up and shut-down phases of the source.
This device will be used for analyzing the beam generated by the ALISES sources developped by the laboratory.
Simulation and characterization of very high intensity ion sources

SL-DRF-24-0459

Research field : Accelerators physics
Location :

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

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

Saclay

Contact :

Guillaume Ferrand

Juliette PLOUIN

Starting date : 01-03-2024

Contact :

Guillaume Ferrand
CEA - DRF/IRFU/DACM

01 69 08 59 64

Thesis supervisor :

Juliette PLOUIN
CEA - DSM/IRFU/SACM/LISAH

+33 169 08 12 65

Light ion accelerators (such as protons and deuterons) at very high intensity (typically exceeding 50 mA) have numerous applications in various fields of physics. From the IFMIF accelerator project, to characterize future materials for fusion reactors, to IPHI-Neutrons, to produce images through neutron radiography, CEA is involved in many projects that require the design and construction of very high-intensity ion sources. The increasing demand for intensity and beam quality from these ion sources requires a better understanding and prediction of their operation.
Ion sources are composed of a plasma chamber inserted into a magnetic coil, in which a gas heated by an RF wave is injected. The produced ions are extracted from the chamber using an electric field applied to extraction electrodes. Their operation depends on a large number of parameters. Determining an ideal set of parameters is very complex to achieve, and no software currently exists to reliably predict its proper functioning.
CEA has been working for several years on the design of a test bench, BETSI, to test and optimize various ion sources for future accelerator projects. Experimental campaigns have been conducted in the past on this test bench to systematically test sets of parameters.
In the context of this thesis, we propose to develop a simulation code that takes into account all the parameters that we can qualify on BETSI (from past experiments or new ones). We will be able then to use the code to propose new sources for upcoming accelerator projects.
Inverse Problems in Astrophysics and Machine Learning

SL-DRF-24-0271

Research field : Artificial intelligence & Data intelligence
Location :

Direction d’Astrophysique (DAP)

Laboratoire CosmoStat (LCS)

Saclay

Contact :

Samuel Farrens

Jean-Luc STARCK

Starting date : 01-01-2024

Contact :

Samuel Farrens
CEA - DRF/IRFU/DAP/LCS

28377

Thesis supervisor :

Jean-Luc STARCK
CEA - DRF/IRFU/DAP/LCS

01 69 08 57 64

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

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

AI (artificial intelligence) is significantly changing the way we solve inverse problems in astrophysics.
In radio interferometry, the detection of radio sources and their classification require taking into account numerous effects such as non-Gaussian noise, incomplete sampling of Fourier space, and the need to construct a sufficient data set for the training. The difficulty increases when the source to be reconstructed evolves over time. Such examples of temporal variations are found in various inverse problems in astrophysics such as transient objects (supernovae, fast radio burst, etc.). ARGOS is a pilot study for a radio interferometer that will perform real-time continuous wide-field observations in centimetre wavelengths. The combination of a wide field of view with high sensitivity will allow ARGOS to detect transient sources that vary on timescales shorter than one second. ARGOS will be able to detect thousands of fast radio bursts per year. These events will need to be accurately differentiated from other transient sources detected by ARGOS, such as supernovae, gamma-ray bursts, white dwarfs, neutron stars, blazars, etc. Given the short time scales of some of these transient events and the need for quick follow up, ARGOS will require state-of-the-art classification solutions employing cutting-edge machine learning architectures. This thesis consists of developing innovative tools from machine learning to solve image reconstruction and source classification problems.
Artificial Intelligence for Mass Measurement of Exotic Isotopes

SL-DRF-24-0416

Research field : Artificial intelligence & Data intelligence
Location :

Département Grand Accélérateur National d’Ions Lourds

Grand Accélérateur National d’Ions Lourds

Saclay

Contact :

Pierre DELAHAYE

Starting date : 01-10-2024

Contact :

Pierre DELAHAYE
CNRS - GANIL/Grand Accélérateur National d’Ions Lourds

02 31 45 4539

Thesis supervisor :

Pierre DELAHAYE
CNRS - GANIL/Grand Accélérateur National d’Ions Lourds

02 31 45 4539

Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2023/10/AIMMEI-thesis2024.pdf

Artificial intelligence opens new perspectives for basic science. It is no exception for nuclear structure studied at the extreme of the nuclear chart by the Super Separator Spectrometer (S3) under construction at GANIL-SPIRAL2. The Piège à Ions Linéaire du Ganil pour la Résolution des Isotopes en Masse (PILGRIM) is a Multi-Reflection time-of-flight Mass Spectrometer (MR-ToF-MS), with state-of-the-art performances that can only be exploited fully thanks to a joint development with the FASTER (http://faster.in2p3.fr/) data acquisition at LPC Caen. The PhD thesis will consist in carrying out this development with the FASTER developers and the physicist in charge of PILGRIM. Machine learning techniques will have to be employed to recognize patterns in the time-of-flight of ions extracted as bunches from the S3 Low Energy Branch. For each individual ion, the time of flight will have to be determined with sub-nanosecond precision, correcting for effects due to pile-up, gain and baseline fluctuations. This development should lead to the determination of masses of exotic nuclei with exquisite precision, enabling tests of nuclear physics models in previously uncharted territories.
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).
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.
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.
X-ray cosmology from deep learning

SL-DRF-24-0346

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

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

Saclay

Contact :

Marguerite PIERRE

Starting date : 01-10-2024

Contact :

Marguerite PIERRE
CEA - DRF/IRFU/SAp/LCEG

0169083492

Thesis supervisor :

Marguerite PIERRE
CEA - DRF/IRFU/SAp/LCEG

0169083492

Laboratory link : https://irfu.cea.fr/dap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=972

Clusters of galaxies are the most massive entities in the universe.
Applying artificial intelligence to the cosmological analysis of X-ray cluster surveys allows us to tackle this problem from a totally new perspective. Only directly observable parametres are used (redshift, X-ray colour and flux) in a deep learning approach based on hydrodynamical simulations; this allows us to establish an implicit link between the X-ray parameters and the underlying dark matter distribution. From this, we can infer the cosmological parameters, without explicitly computing cluster masses and bypassing the empirical formalism of scaling relations between the X-ray properties and cluster masses.
The goal of the thesis is to apply this method (developed at DAP) to the XMM-XXL survey, which is, 24 years after the XMM launch, the only programme having assembled a cosmological cluster sample with controlled selection effects (~ 400 objects). The expected results will constitute a first in the history of observational cosmology.
Study of the dynamics of the solar corona and wind at the maximum of magnetic cycle 25

SL-DRF-24-0390

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire de dynamique des étoiles des (Exo) planètes et de leur environnement (LDE3)

Saclay

Contact :

Barbara PERRI

Allan Sacha BRUN

Starting date : 01-10-2024

Contact :

Barbara PERRI
CEA - DRF/IRFU/DAP/LDE3


Thesis supervisor :

Allan Sacha BRUN
CEA - DSM/IRFU/DAp/LDE3

+33 1 69 08 76 60

Personal web page : https://fr.linkedin.com/in/barbara-perri-919773a5/en

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

More : https://wholesun.eu

The Sun's activity is modulated according to an average 11-year magnetic cycle, with the next maximum expected in 2025. This increase in activity implies greater temporal variability for our star, both in terms of its magnetic field, with intense structures appearing and disappearing at a higher rate, and in terms of its atmosphere, which will produce a wind of charged particles that varies in speed and density. These variations have major consequences for the Earth, as it becomes more difficult to predict their impact on our technological society, such as radio blackouts or electrical surges. One of the greatest challenges facing space weather forecasting today is to provide reliable forecasts for the most variable events, which are often also the most extreme.
This thesis proposes to take advantage of the unprecedented conjunction of observations available for the next solar maximum with the Parker Solar Probe and Solar Orbiter space probes, in order to significantly improve the available solar wind models. The student will be able to calibrate the Wind Predict-AW 3D MHD model, one of the most advanced in Europe, to characterize its ability to reproduce conditions of maximum activity. This characterization will involve automated comparisons with different solar datasets, on highly parallel simulations (HPC) producing Big Data-scale results. He will also participate in the development of a new model capable of evolving magnetograms over time, based on the magneto-frictional approach and the evolution of the photospheric electric field - the most advanced techniques for the temporal evolution of magnetic structures - and will use them to quantify the information missing at maximum solar activity, and thus improve space weather forecasts.
Measuring the assembly of massive primordial galaxies with the James Webb Space Telescope (JWST)

SL-DRF-24-0411

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

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

Saclay

Contact :

Benjamin MAGNELLI

Starting date : 01-10-2024

Contact :

Benjamin MAGNELLI
CEA - DRF/IRFU

0169086825

Thesis supervisor :

Benjamin MAGNELLI
CEA - DRF/IRFU

0169086825

The James Webb Space Telescope (JWST) is revolutionizing our view of the first billion years after the big bang, by enabling us to detect the primordial galaxies formed by the collapse of the Universe's first overdensities. Initial studies of the properties of these galaxies, partly carried out by our team, have revealed that their formation is still largely misunderstood and potentially in tension with the Lambda Cold Dark Matter (LCDM) model. Indeed, these studies have uncovered a potential excess of massive primordial galaxies, implying accelerated growth of these galaxies at star formation efficiencies well beyond the predictions of theoretical models. Before invoking radically different cosmological and galaxy evolution models, however, it is necessary to confirm these tensions, which are currently based only on highly uncertain measurements of the stellar mass of a few galaxies.
The aim of this thesis is to confirm or refute these tensions by accurately constraining, for the first time, the stellar mass of a large statistical sample of primordial galaxies. To do this, we will combine data from four JWST extragalactic surveys with an original statistical approach of image stacking, enabling us to obtain the average stellar mass of primordial galaxies that are otherwise too faint to be detected individually by the JWST in the critical mid-infrared window. This information, together with that obtained on their star-forming activity, will be decisive in understanding the growth of the Universe's first galaxies.
Cosmological Simulations of Galaxy Formation with Exascale Supercomputing

SL-DRF-24-0395

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

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

Saclay

Contact :

Camila CORREA

Starting date : 01-09-2024

Contact :

Camila CORREA
CEA - DRF/IRFU/DAp/LCEG

31653850353

Thesis supervisor :

Camila CORREA
CEA - DRF/IRFU/DAp/LCEG

31653850353

Personal web page : https://www.camilacorrea.com

Laboratory link : https://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=977

This project aims to enhance the synergy between astronomical observations, numerical cosmological simulations and galaxy modelling. Upcoming instruments like Euclid, DESI and Rubin LSST, among others, will make wide-field galaxy surveys with extremely precise measurements. The enhanced precision in the observations however, will requite robust theoretical predictions from galaxy formation models to achieve a profound understanding of the fundamental physics underlying the cosmological measurements.

To achieve this, exa-supercomputers will play a key role. Unlike modern supercomputers, which typically consist of thousands of CPUs for state-of-the-art simulation productions, exa-supercomputers will employ a hybrid configuration of CPUs hosts with GPUs accelerators. This configuration will empower the computations of up to 10^18 operations per second. Exa-supercomputers will revolutionise our ability to simulate cosmological volumes spanning 4 Gigaparsecs (Gpc) with 25 trillion particles! the minimum volume and resolution requirements necessary for making predictions of Euclid data.

However, the challenge to-date lies in the fact that cosmological simulation software designed for exa-supercomputers lacks the modelling for galaxy formation. Examples include the HACC-CRKSPH code (Habib et al. 2016, Emberson et al. 2019) and PKDGRAV3 (Potter, Stadel & Teyssier 2017), that have produced the largest simulations to-date, FarPoint (Frontiere et al. 2022), encompassing 1.86 trillion particles within a 1 Gpc volume, and Euclid Flagship (Potter, Stadel & Teyssier 2017), featuring 2 trillion particles in a 3 Gpc volume, respectively. While HACC-CRKSPH and PKDGRAV3 were developed to run on modern GPUs-accelerated supercomputers, they lack the complex physics of galaxy formation and can therefore only produce gravity-only cosmological boxes.

The SWIFT code (Schaller et al. 2023) is a parallel effort that has produced Flamingo (Schaye et al. 2023), the largest simulation that integrates gravity, hydrodynamics and galaxy formation physics, encompassing 0.3 trillion particles. However, the caveat of SWIFT is that it was primarily designed for CPU usage. The adaptation of SWIFT to run on modern GPUs will require the entire redevelopment of the code. Another example are the current big simulations of galaxy formation done at Irfu, such as Extreme Horizon (Chabanier et al. 2020), that have also reached their limit as they rely on CPU-based codes that hamper their scalability.

Understanding the intricacies of galaxy formation is paramount for interpreting astronomical observations. In this pursuit, CEA DRF/Irfu stands uniquely positioned to lead the advances in astrophysics in the emerging exascale era. Researchers at DAp and DPhP have already embarked on the analysis of high-quality data from the Euclid mission and DESI. Simultaneously, a team at DEDIP is developing DYABLO (Durocher & Delorme, in preparation), a robust gravity + hydrodynamics code tailored explicitly for exa-supercomputing.

In recent years, significant investments have been channeled into the advancement of DYABLO. Numerous researchers at DAp and DEDIP have contributed on various aspects (from the hydrodynamics of solar physics to refining Input/Output processes) thanks to collaborative grants such as PTC-CEA grant and FETHPC European project IO-SEA. Additionally, DYABLO has benefited from interactions with CEA research unit, Maison de la simulation (CEA & CNRS).

This ambitious project aims to extend DYABLO's capabilities by integrating galaxy formation modules in collaboration with Maxime Delorme. These modules will encompass radiative gas cooling and heating, star formation, chemical enrichment, stellar mass loss, energy feedback, black holes, and active galactic nuclei feedback. The ultimate objective is to enhance the analysis of Euclid and DESI data by generating simulation predictions of galaxy formation and evolution using DYABLO. The initial dataset will involve a comprehensive examination of clustering of matter and galaxy clustering, in partnership with researchers at DAp/LCEG and DAp/CosmoStat.

This thesis will create the first version of a galaxy formation code optimised for exa-scale supercomputing. Ongoing developments will not only expand its capabilities but also unlock new opportunities for in-depth research, enhancing synergy between astronomical observations, numerical cosmological simulations, and galaxy modelling.

References:
Habib, S., et al., 2016, New Astronomy, Volume 42, p. 49-65.
Emberson, J.D., et al., 2019, The Astrophysical Journal, Volume 877, Issue 2, article id. 85, 17 pp.
Potter, D., Stadel, J., & Teyssier, R., 2017, Computational Astrophysics and Cosmology, Vol. 4, Issue 1, 13 pp.
Frontiere, N., et al., 2023, The Astrophysical Journal Supplement Series, Volume 264, Issue 2, 24 pp.
Schaller, M., et al., 2023, eprint arXiv:2305.13380
Schaye, J., et al., 2023, eprint arXiv:2306.04024
Chabanier, S., et al., 2020, Astronomy & Astrophysics, Volume 643, id. L8, 12 pp.
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.
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 (GCOSMO)

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
Multi-messenger analysis of core-collapse supernovae

SL-DRF-24-0441

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire de modélisation des plasmas astrophysiques (LMPA)

Saclay

Contact :

Jérôme Guilet

Thierry FOGLIZZO

Starting date : 01-10-2024

Contact :

Jérôme Guilet
CEA - DRF/IRFU/DAP/LMPA

06 38 62 46 30

Thesis supervisor :

Thierry FOGLIZZO
CEA - DRF/IRFU/DAP/LMPA

01 69 08 87 20

Personal web page : https://www.youtube.com/watch?v=-IjAwszbiO8

Core-collapse supernovae play a crucial role in the stellar evolution of massive stars, the birth of neutron stars and black holes, and the chemical enrichment of galaxies. How do they explode? The explosion mechanism can be revealed by the analysis of multi-messenger signals: the production of neutrinos and gravitational waves is modulated by hydrodynamic instabilities during the second following the formation of a proto-neutron star.
This thesis proposes to use the complementarity of multi-messenger signals, using numerical simulations of the stellar core- collapse and perturbative analysis, in order to extract physical information on the explosion mechanism.
The project will particularly focus on the multi-messenger properties of the stationary shock instability ("SASI") and the corotational instability ("low T/W") for a rotating progenitor. For each of these instabilities, the signal from different species of neutrinos and the gravitational waves with different polarization will be exploited, as well as the correlation between them.

SL-DRF-24-0372

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire de dynamique des étoiles des (Exo) planètes et de leur environnement (LDE3)

Saclay

Contact :

Antoine Strugarek

Starting date : 01-10-2024

Contact :

Antoine Strugarek
CEA - DRF/IRFU/DAP/LDE3

0169083018

Thesis supervisor :

Antoine Strugarek
CEA - DRF/IRFU/DAP/LDE3

0169083018

Personal web page : https://irfu.cea.fr/Pisp/antoine.strugarek/index.html

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

Understanding the formation of bulges based on morphology and kinematics information from JWST

SL-DRF-24-0383

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

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

Saclay

Contact :

Emanuele DADDI

Starting date : 01-10-2024

Contact :

Emanuele DADDI
CEA - DRF/IRFU/DAP/LCEG


Thesis supervisor :

Emanuele DADDI
CEA - DRF/IRFU/DAP/LCEG


Present-day bulges of spiral galaxies and elliptical galaxies contain very old stars and are thought to be formed in the early Universe. How this actually happened in practice is not well understood, and the most relevant physical processes at play are still unclear. In the last decade, evidence has been growing of the existence of compact star bursting galaxies that might be signposts of bulges caught at the event of formation. More recently, also thanks to new findings from our group based on JWST, a number of further puzzling results has accumulated, currently difficult to explain: A) these star-bursting galaxies are always embedded in larger disk-like systems that are less active but contain most of the existing stellar mass, as if there was no ’naked’ bulge formation; B) in some cases, the outer disks have actually stopped forming stars, thus representing cases of quenching progressing from the outside-in, reversing the standard more familiar pattern (as observed in local spirals and the MilkyWay, where the center is quenched and the outskirts are forming stars); C) the disks are often strongly lopsided in their stellar mass distribution, a feature becoming more and more dominant when looking at earlier times. This phenomenology is currently unexplained. It could be related to merging activity, gas accretion or also feedback effects. If these are forming bulges, how they would evolve in present-day bulges and elliptical galaxies is unclear. Still, these new challenging observations promise breakthrough in the understanding of bulge formation if more progress can be made and further insight gathered. We propose a PhD project where the student will be using imaging and spectroscopy data from JWST to illuminate these issues. Imaging from deep and ultra deep public surveys that is accumulating will be used to increase the statistics and put on more solid grounds the early results gathered so far. The spectroscopy from JWST holds the key to detailed understanding of specific systems, providing information on kinematics of the compact star bursting cores as well as of the outer disks: if these subsystems are co-rotating without major disturbances would support non violent, gas accretion related evolution. On the contrary, counter-rotating subsystems or kinematics disturbances would betray merging events. This kind of test has not yet been carried out. We will use targeted spectroscopy in part already available from the Early-Release project CEERS of which we are members, from the large archive that is accumulating, and from dedicated proposals (pending, and to be submitted in future cycles).

SL-DRF-24-0314

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire de modélisation des plasmas astrophysiques (LMPA)

Saclay

Contact :

Matthias GONZALEZ

Starting date :

Contact :

Matthias GONZALEZ
Université Paris Cité - DRF/IRFU/DAp/LMPA

33 1 69 08 17 79

Thesis supervisor :

Matthias GONZALEZ
Université Paris Cité - DRF/IRFU/DAp/LMPA

33 1 69 08 17 79

Disequilibrium chemistry of exoplanet atmospheres in the JWST era. An opportunity for Machine Learning.

SL-DRF-24-0397

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

Laboratoire de dynamique des étoiles des (Exo) planètes et de leur environnement (LDE3)

Saclay

Contact :

Antonio Garcia Muñoz

Starting date :

Contact :

Antonio Garcia Muñoz
CEA - DRF/IRFU/DAP/LDE3


Thesis supervisor :

Antonio Garcia Muñoz
CEA - DRF/IRFU/DAP/LDE3


Personal web page : https://antoniogarciamunoz.wordpress.com/

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

In little more than one year of scientific operations, JWST has already revolutionized our understanding of exoplanets and their atmospheres. The ARIEL space mission, to be launched in 2029, will contribute in due course to this revolution. A main finding that has been enabled by the exquisite quality of the JWST data is that exoplanet atmospheres are in chemical disequilibrium. A full treatment of disequilibrium is both complex and computationally expensive. In a first step, our project will numerically investigate the extent of chemical disequilibrium in the atmospheres of JWST targets. We will use towards that end an in-house photochemical model. In a second step, our project will explore Machine Learning (ML) techniques to emulate the outputs of the full photochemical model at a reduced computational cost. The performance of the ML-based emulator will be analyzed with the ultimately goal of its integration into atmospheric retrieval models. The proposed project combines the sophisticated physics and chemistry of exoplanet atmospheres with developments in new numerical techniques.
A window on interstellar nanoparticle evolution: the NIKA2 images of nearby galaxies

SL-DRF-24-0323

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

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

Saclay

Contact :

Frédéric Galliano

Starting date : 01-10-2024

Contact :

Frédéric Galliano
CNRS - UMR AIM

01 69 08 18 21

Thesis supervisor :

Frédéric Galliano
CNRS - UMR AIM

01 69 08 18 21

Personal web page : https://irfu.cea.fr/Pisp/frederic.galliano/

Laboratory link : https://irfu.cea.fr/dap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=973

Interstellar nanoparticles are a major physical component of galaxies, reprocessing starlight, controlling the heating and cooling of the gas, catalyzing chemical reactions and regulating star formation. The abundance, composition, structure and size distribution of these small solid particles, mixed with the interstellar gas, are however poorly-known. They indeed evolve within the interstellar medium and present systematic differences among galaxies. It is thus crucial to obtain detailed, carefully analyzed, empirical constraints of these properties, in a wide diversity of environments. Progress in this field are absolutely necessary to properly interpret observations of nearby star-forming regions and distant galaxies, as well as for precisely modeling interstellar physics.

Of particular interest are the long-wavelength optical properties of the nanoparticle mixture in the millimeter range. This spectral window is currently the least known. Yet, the millimeter opacity of the grain mixture has a central importance, since mass estimates based on spectral energy distribution fitting primarily rely on this quantity. A bias or systematic evolution of the millimeter opacity will directly translate in an inaccuracy in the nanoparticle mass, which is often used as a proxy to infer the gas mass of a region or galaxy.

Our guaranteed time program, IMEGIN (Interpreting the Millimeter Emission of Galaxies at IRAM with NIKA2; PI Madden; 200 hours), with the NIKA2 camera at the 30-m IRAM radiotelescope, has fully mapped 20 nearby galaxies at 1.2 mm and 2 mm. In addition, our open time program, SEINFELD (Submillimeter Excess In Nearby Fairly-Extended Low-metallicity Dwarfs; PI Galliano; 36 hours), is completing the survey down to low-metallicities (the metallicity is the relative abundance of elements heavier than Helium). These new and exceptional data are the first good quality maps of resolved galaxies at millimeter wavelengths, allowing us to study how the grain properties vary with the physical conditions.

The goal of the present PhD project is to combine these observations with other, already existing, multi-wavelength data (in particular, WISE, Spitzer and Herschel), in order to demonstrate how the millimeter opacity depends on the local physical conditions. The first step will consist in processing and homogenizing the data. The student will also have the opportunity to participate in our observing campaigns at Pico Veleta. In a second time, the student will model the spatially-resolved emission, using our in-house, state-of-the-art hierarchical Bayesian code, HerBIE. This will allow the student to produce maps of the nanoparticle properties and compare them to maps of the physical conditions. Finally, these results will be used to model the evolution timescales of the grain properties under the effects of radiation field and gas accretion. The laboratory measurements recently produced by the Toulouse group will be put to profit. This work will be performed within the IMEGIN international collaboration.
How large are dust particles at the onset of disk formation ? A multi-wavelength investigation

SL-DRF-24-0321

Research field : Astrophysics
Location :

Direction d’Astrophysique (DAP)

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

Saclay

Contact :

Anaëlle MAURY

Starting date : 01-10-2024

Contact :

Anaëlle MAURY
CEA - DRF/IRFU/SAp/LFEMI

0169083161

Thesis supervisor :

Anaëlle MAURY
CEA - DRF/IRFU/SAp/LFEMI

0169083161

The formation and properties of exoplanetary systems is a fascinating question, which has been at the heart of our quest to define mankind and the conditions for life to develop in a broader context. Observations suggest there should be billions of planets in our Galaxy alone. What are the physical process that make planet formation so likely ? Which local conditions are required to transform the stardust of the interstellar medium into pebbles around young stars, and grow these further into planets ? Investigating the dust evolution along the star formation sequence is key to provide a complete picture of the planet formation scenario.
Moreover, the dust grains are crucial because they regulate some key physical processes: for example, the amount of small grains is a key parameter to set the coupling of magnetic fields, hence regulating the sizes and masses of the protostellar disks when they are assembled.

Recently, the star formation group at CEA has obtained some of the first observational clues that the dust particles contained in the pristine disk-forming reservoirs that are the embedded protostars may already have significantly evolved from the submicronic dust populating the interstellar medium.
The proposed PhD aims at exploring new dataset, observations of young protostars from the infrared to the millimeter wavelengths and investigate wether dust particles are indeed growing significantly already during the first 0.5 Myrs of the star formation process.
To improve our understanding of early dust evolution during the disk-building phase, this analysis of multi-scale observational data will be compared to the predictions of evolved dust models implemented in MHD numerical simulations of disk formation.

The student will analyze data obtained with the NIRSpec/NIRCam, then MIRI, instruments aboard the James webb Space Telescope, towards nearby embedded protostars. This data should probe the presence of micronic dust grains in the close vicinity of the young forming disks. The analysis of complementary dust emission maps from the ALMA and NOEMA interferometers, probing the colder dust, will complete the picture, allowing a multi-wavelength approach to constrain the models.
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.
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.
MACHINE LEARNING FOR INVERSE PROBLEMS IN HADRON STRUCTURE

SL-DRF-24-0306

Research field : Nuclear Physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire structure du nucléon (LSN) (LSN)

Saclay

Contact :

Valerio Bertone

Hervé Moutarde

Starting date : 01-10-2024

Contact :

Valerio Bertone
CEA - DRF/IRFU/DPhN/LSN


Thesis supervisor :

Hervé Moutarde
CEA - DRF/IRFU/DPhN

33 1 69 08 32 06

Laboratory link : https://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=4189

Characterizing the multidimensional structure of hadrons in terms of quarks and gluons is one of the major objectives of hadronic physics today. This is not only the central theme of many experimental facilities worldwide, but also one of the main reasons for the construction of future colliders in the USA and China. It is also one of the key areas of research for intensive numerical simulations of the strong interaction. However, in both cases, the connection between measured and simulated data on the one hand, and the multidimensional structure of hadrons on the other, is not direct. The data are linked to the hadron structure via mathematically ill-posed multidimensional inverse problems. It has been shown that these inverse problems lead to a significant increase in uncertainties, to the point of becoming the dominant source of uncertainty in some cases. The aim of this thesis is to use machine learning tools to assess, reduce and correctly propagate uncertainties from experimental or simulation data to the multidimensional structure of hadrons. The strategy for achieving this is to develop an original neural network architecture capable of taking into account the full range of theoretical properties arising from quantum chromodynamics, and then to adapt it to inverse problems linking experimental and simulation data to the 3D structure of hadrons.
Uncertainty propagation in a Monte-Carlo transport code

SL-DRF-24-0367

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire etudes et applications des reactions nucleaires (LEARN) (LEARN)

Saclay

Contact :

Jean-Christophe DAVID

Starting date : 01-10-2024

Contact :

Jean-Christophe DAVID
CEA - DRF/IRFU/DPhN/LEARN

0169087277

Thesis supervisor :

Jean-Christophe DAVID
CEA - DRF/IRFU/DPhN/LEARN

0169087277

Laboratory link : https://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=2105

Nuclear reaction modeling has been continuously being improved for many decades now. That's especially the case for our nuclear cascade code INCL. An ANR project has been funded for the next four years (2024-2027) to work on the issue of uncertainty and error estimate. Since this code is implemented in the particle transport code Geant4, the next step is to propagate these uncertainties from INCL to Geant4. There was a recent study on uncertainty propagation, called Transport Monte Carlo (TMC). However, this study only addresses the propagation of uncertainties related to model parameters, there was no propagation of model biases (related to hypotheses) and their uncertainties, which are both outside the physical model. Therefore, the propagation of biases and their uncertainties, which are coming from Monte Carlo collision models, is unexplored territory. The aim of the proposed PhD project is then to develop methods for this kind of propagation and to study the functioning and features of the developed methods in schematic scenarios. The full implementation of the developed methods into a transport code, such as GEANT4, however, is not within the core scope of the thesis, but it might be possible if time permits.
Study of clustering using low-energy reactions induced by neutron-rich oxygen isotopes

SL-DRF-24-0415

Research field : Nuclear physics
Location :

Département Grand Accélérateur National d’Ions Lourds

Grand Accélérateur National d’Ions Lourds

Saclay

Contact :

Abdelouahad CHBIHI

Starting date : 01-10-2024

Contact :

Abdelouahad CHBIHI
CNRS - GANIL -UPR3266

02 31 45 4708

Thesis supervisor :

Abdelouahad CHBIHI
CNRS - GANIL -UPR3266

02 31 45 4708

Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2023/10/ClusterO20-thesis2024.pdf

MODELLING LIGHT ANTI-ION REACTIONS ON ATOMIC NUCLEI

SL-DRF-24-0347

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire etudes et applications des reactions nucleaires (LEARN) (LEARN)

Saclay

Contact :

Jean-Christophe DAVID

Starting date : 01-10-2024

Contact :

Jean-Christophe DAVID
CEA - DRF/IRFU/DPhN/LEARN

0169087277

Thesis supervisor :

Jean-Christophe DAVID
CEA - DRF/IRFU/DPhN/LEARN

0169087277

Laboratory link : https://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=2105

The anti-(p, n, d, t, 3He, 4He)-nucleus reactions are both instructive and complicated to study. In addition to knowledge of the products of the antinuclon-nucleon reaction, they require the- nuclear environment to be taken into account, in particular the interactions in the final state.
Antiproton-nucleon reactions are/will be used/studied in particular at Cern's antiproton decelerator (AD) ring and at the FAIR facility in Germany to understand the behaviour oft antimatter. Reactions with light anti-ions (dbar, 3He-bar, for example) are of more recent interest, in particular with the GAPS (General AntiParticle Spectrometer) experiment, which aims to measure the fluxes of these particles in cosmic rays. The idea is to identify dark maJer, of which these particles are decay products, and whose measured quantities could 'easily' emerge from the cosmic background noise.
Recently, antiproton-nucleus reactions have been added to the INCL (IntraNuclear Cascade Liège) nuclear reaction code developed at the CEA (Irfu/DPhN) and this code is currently being implemented in the Geant4 transport code. The aim of the proposed thesis is to now include the reactions anti-(d, t, 3He, 4He)-nucleus in the INCL code.
Study of pear-shaped nuclei using the new detector SEASON

SL-DRF-24-0312

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Damien THISSE

Marine VANDEBROUCK

Starting date : 01-10-2024

Contact :

Damien THISSE
CEA - DRF/IRFU/DPhN


Thesis supervisor :

Marine VANDEBROUCK
CEA - DRF/IRFU/DPhN


Understanding the limits of existence of the nucleus, especially concerning its mass limit, is one of the major fields of research in contemporary nuclear physics. In the region of heavy nuclei, neutron-deficient actinides are of particular interest. Indeed, pronounced octupole (pear-shaped) deformations are predicted and have even been observed in some nuclei. The aim of this thesis is to study these octupole deformed nuclei using the new-generation detector SEASON, whose detection efficiency and energy resolution are unprecedented for this type of experiment. The thesis work will focus on the installation, testing, experimental data-taking and analysis from an experiment to be carried out in 2025 at the University of Jyväskylä. In this experiment, the proton-induced fusion-evaporation reaction 232Th(p,X)Y will be used to populate neutron-deficient actinide isotopes, whose decay products will be analyzed using SEASON. The thesis will be in cotutelle with the University of Jyväskylä and divided into two parts:
i) a 1-year period at the University of Jyväskylä, during which the experiment will take place
ii) the following two years at CEA Saclay will be devoted to data analysis and preparation of the experimental program with SEASON at the new facility S3-LEB at GANIL-SPIRAL2.
INVESTIGATION OF THE NUCLEAR TWO-PHOTON DECAY IN SWIFT FULLY STRIPPED HEAVY IONS

SL-DRF-24-0289

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Wolfram KORTEN

Starting date : 01-10-2024

Contact :

Wolfram KORTEN
CEA - DRF/IRFU/DPhN/LENA

+33169084272

Thesis supervisor :

Wolfram KORTEN
CEA - DRF/IRFU/DPhN/LENA

+33169084272

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

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

More : https://www.gsi.de/en/work/research/appamml/atomic_physics/experimental_facilities/esr.htm

The nuclear two-photon, or double-gamma decay is a rare decay mode in atomic nuclei whereby a nucleus in an excited state emits two gamma rays simultaneously. Even-even nuclei with a first excited 0+ state are favorable cases to search for a double-gamma decay branch, since the emission of a single gamma ray is strictly forbidden for 0+ ? 0+ transitions by angular momentum conservation. The double-gamma decay still remains a very small decay branch (<1E-4) competing with the dominant (first-order) decay modes of atomic internal-conversion electrons (ICE) or internal positron-electron (e+-e-) pair creation (IPC). Therefore we will make use of a new technique to search for the double-gamma decay in bare (fully-stripped) ions, which are available at the GSI facility in Darmstadt, Germany. The basic idea of our experiment is to produce, select and store exotic nuclei in their excited 0+ state in the GSI storage ring (ESR). For neutral atoms the excited 0+ state is a rather short-lived isomeric state with a lifetime of the order of a few tens to hundreds of nanoseconds. At relativistic energies available at GSI, however, all ions are fully stripped of their atomic electrons and decay by ICE emission is hence not possible. If the state of interest is located below the pair creation threshold the IPC process is not possible either. Consequently, bare nuclei are trapped in a long-lived isomeric state, which can only decay by double-gamma emission to the ground state. The decay of the isomers would be identified by so-called time-resolved Schottky Mass Spectroscopy. This method allows to distinguish the isomer and the ground state state by their (very slightly) different revolution time in the ESR, and to observe the disappearance of the isomer peak in the mass spectrum with a characteristic decay time. After a first successful experiment establishing the double-gamma decay in 72Ge a new experiment has been accepted by the GSI Programme Committee and its realization is planned for 2024.
Exploring magicity and nuclear forces in 68Ni

SL-DRF-24-0407

Research field : Nuclear physics
Location :

Département Grand Accélérateur National d’Ions Lourds

Grand Accélérateur National d’Ions Lourds

Saclay

Contact :

Olivier SORLIN

Starting date : 01-10-2024

Contact :

Olivier SORLIN
CNRS - GANIL/Grand Accélérateur National d’Ions Lourds

02 31 45 4525

Thesis supervisor :

Olivier SORLIN
CNRS - GANIL/Grand Accélérateur National d’Ions Lourds

02 31 45 4525

Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2023/10/NICKEL-thesis2024.pdf

We propose to study the magicity of 68Ni by means of neutron adding and neutron removal transfer reactions (d,p) and (p,d), respectively. This way, we get unique access to the occupancy of the normally occupied orbits and the vacancy of the valence ones. If a sharp transition in occupancy is found, the nucleus is considered as magic, otherwise rather superfluid. Furthermore, this study also allows to study the spin-orbit force, essential to the modeling of atomic nuclei, in a unique manner. 68Ni is produced by means of the LISE spectrometer at GANIL, protons and deuterons produced arising from transfer reactions are detected in the highly-segmented Si array MUST2, gamma-rays with EXOGAM2 and incoming/outgoing nuclei tracks, energy losses and time-of-flights with sets of gas-filled detectors.
DESIGN OF A MONOLITHIC PIXEL SENSOR FOR PARTICLE PHYSICS WITH AN EMBEDDED ADAPTIVE READOUT ELECTRONICS

SL-DRF-24-0349

Research field : Nuclear physics
Location :

Département d’Electronique, des Détecteurs et d’Informatique pour la physique (DEDIP)

Systèmes Temps Réel, Electronique d’Acquisition et Microélectronique

Saclay

Contact :

Fabrice Guilloux

Stefano PANEBIANCO

Starting date : 01-10-2024

Contact :

Fabrice Guilloux
CEA - DRF/IRFU/DEDIP/STREAM

33 1 69 08 67 31

Thesis supervisor :

Stefano PANEBIANCO
CEA - DRF/IRFU/DPhN/LQGP

0169087357

In current and future high-energy physics experiments (i.e. upgrades of large detectors at the LHC and experiments in future colliders), the granularity of particle detectors continues to increase, and the use of multi-channel submicron integrated circuits has become a standard.

This granularity was taken one step further in the field of "Monolithic Active Pixel Sensor" (MAPS) technology, where pixel sizes can be as small as 10 x 10 µm2. These small pixels make it possible to achieve record spatial resolutions or greatly improve the radiation resistance of the trace detector, at the cost of a large quantity of data produced. This large amount of data is acceptable where a maximum spatial resolution is required, but can be prohibitive when this is not necessary, or when space and consumption constraints put limits on the number of fast downstream links.

Each experiment therefore requires to redefine the combination of the pixel size and the architecture of the detector's readout electronics, in order to meet the occupancy rate requirements of each physics experiment, and the detector's readout capabilities.
A major innovation in the design of pixel sensors for particle physics is to decouple the pixel matrix from the data rate sent.
As part of a team that has been developing MAPS since 1999, the approach required for the thesis is in a first step to study the existing trace detector architecture in order to understand its limitations in terms of radiation resistance. In a second step, the thesis will focus on information grouping options, assessing the impact of these options on data reduction as well as on induced information loss.

This will be supported by the design of a system-on-chip architecture, including pixel array optimization and digital processing, validating the work carried out in an integrated circuit.

To this end, this thesis will focus specifically on one of the major experiments at the European Center for Nuclear Research (CERN): the Upstream Tracker detector for the LHC Beauty Quark Experiment (LHCb).
Imaging with Micromegas detectors with Optical readout

SL-DRF-24-0102

Research field : Nuclear physics
Location :

Département d’Electronique, des Détecteurs et d’Informatique pour la physique (DEDIP)

DÉtecteurs: PHYsique et Simulation

Saclay

Contact :

Thomas PAPAEVANGELOU

Esther FERRER RIBAS

Starting date : 01-10-2024

Contact :

Thomas PAPAEVANGELOU
CEA - DRF/IRFU/DEDIP/DEPHYS

01 69 08 2648

Thesis supervisor :

Esther FERRER RIBAS
CEA - DRF/IRFU/DEDIP/DEPHYS

0169083852

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

Laboratory link : https://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_sstheme.php?id_ast=4218

Recent developments have shown that coupling a Micromegas gaseous detector on a glass substrate with a transparent anode and a CCD camera enable the optical readout of Micromegas detectors with an impressive spatial resolution showing that the glass Micromegas detector is well-suited for imaging. This feasibility test has been effectuated with low-X-ray photons permitting energy resolved imaging. This test opens the way to different applications. Here we will focus, on one hand, on neutron imaging for non-destructive examination of highly gamma-ray emitting objects, such as fresh irradiated nuclear fuel or radioactive waste and on the other hand, we would like to develop a beta imager at the cell level in the field of anticancerous drug studies.
Both applications require gas simulations to optimize light yields, optimization of the camera operation mode and design of the detectors in view of the specific constraints of reactor dismantling and medical applications: spatial resolution and strong gamma suppression for neutron imaging and precise rate and energy spectrum measurements for the beta. The image acquisition will be optimized for each case and dedicated processing algorithms will be developed.
Unified theory of nuclear structure and reactions in the open quantum system framework

SL-DRF-24-0322

Research field : Nuclear physics
Location :

Département Grand Accélérateur National d’Ions Lourds

Grand Accélérateur National d’Ions Lourds

Saclay

Contact :

Marek PLOSZAJCZAK

Starting date : 01-10-2024

Contact :

Marek PLOSZAJCZAK
CEA - DRF/IRFU//GANIL

02 31 45 4590

Thesis supervisor :

Marek PLOSZAJCZAK
CEA - DRF/IRFU//GANIL

02 31 45 4590

Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2023/10/GSM24-thesis2024.pdf

Light weakly bound or resonant nuclei play an important role in various stellar processes of nucleosynthesis. The comprehensive understanding of these nuclei requires a correct description of the multi-particle continuum. It is proposed to study complex reactions of astrophysical interest and near-threshold narrow resonances which play crucial role in the nucleosynthesis of heavier elements, using Gamow Shell Model in the representation of coupled channels.
First High Resolution In-gas-jet Laser Spectroscopy at S3LEB

SL-DRF-24-0406

Research field : Nuclear physics
Location :

Département Grand Accélérateur National d’Ions Lourds

Grand Accélérateur National d’Ions Lourds

Saclay

Contact :

Nathalie LECESNE

Hervé SAVAJOLS

Starting date : 01-10-2024

Contact :

Nathalie LECESNE
CNRS - GANIL

0231454472

Thesis supervisor :

Hervé SAVAJOLS
CNRS - GANIL, UPR 3266

02 31 45 4699

Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2023/10/S3LEB-thesis2024.pdf

The objective of this PhD project is to work on the commissioning plan and the first experiment of the S3 Low Energy Branch (S3-LEB), currently under construction at S3 (Super Separator Spectrometer), as part of the SPIRAL2 facility at the GANIL (Grand Accélérateur National d’Ions Lourds) laboratory in Caen, France. The major attribute of the S3-LEB is to use atomic physics techniques - more specifically, high resolution spectral measurements of the atomic transitions – in order to provide fundamental and nuclear-model-independent data on the structure of ground and isomeric nuclear states. In this context, this setup will allow the measurements of static properties of exotic nuclei such as charge radii, electromagnetic moments, nuclear spins and atomic masses, giving information on the distribution of the nucleons inside the nucleus and providing information on structural changes throughout the chart of nuclei. This state-of-the-art technique will be used at S3 with rare beams never studied by low-energy measurements.
Heavy ions beam dynamics in the SPIRAL2 linac and in the S3 separator

SL-DRF-24-0417

Research field : Nuclear physics
Location :

Département Grand Accélérateur National d’Ions Lourds

Grand Accélérateur National d’Ions Lourds

Saclay

Contact :

Bertrand JACQUOT

Fanny FARGET

Starting date : 01-10-2024

Contact :

Bertrand JACQUOT
CNRS - DRF/IRFU/GANIL

023145 46.40

Thesis supervisor :

Fanny FARGET
CNRS - GANIL

0231454857

Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2023/10/LIHIO-thesis2024.pdf

The SPIRAL2 linear accelerator is optimized for light ions (protons, deuterons), but it will also deliver heavier ions (O, Ne, Ar,…Ni) for the S3 spectrometer. The first objective of the PhD, is to propose and study the methods allowing to tune a heavy ion beam in 26 independent accelerating RF cavities in a fast and reproducible way up.
The S3 electromagnetic separator will use the beams from the linac to create and purify radioactive ions with a high efficiency. The complexity of its superconducting magnets requires an optimization of many parameters. Thanks to numerous hexapolar and octupolar corrections, we will be able to reduce the beam optical aberrations. The commissioning of the separator will require numerous measurements with beams and the development of an algorithm to optimize the optics for the 2 different operating modes. The second objective is to provide the simulations tools to nuclear physicists allowing them to prepare their experiments on S3 and to adjust the parameters of the spectrometers during the experiments.
The thesis work will be based on beam dynamics simulations and experimental measurements with beams.

Neutron-star crusts at finite temperature

SL-DRF-24-0403

Research field : Nuclear physics
Location :

Département Grand Accélérateur National d’Ions Lourds

Grand Accélérateur National d’Ions Lourds

Saclay

Contact :

ANTHEA FANTINA

Starting date : 01-10-2024

Contact :

ANTHEA FANTINA
CNRS - GANIL

0231454633

Thesis supervisor :

ANTHEA FANTINA
CNRS - GANIL

0231454633

Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2023/10/NScrust-thesis2024.pdf

Neutron stars are among the densest objects in the universe. Born from the explosion of core-collapse supernovae, they are initially very hot and consequently their outer layers (the crust) are made up of a dense liquid composed of various nuclear species immersed in a background “gas” of electrons (and possibly neutrons/protons).
During the doctoral thesis, a theoretical study of the neutron-star crust at finite temperature will be carried out, in particular with regard to the treatment of nuclei in the dense medium characterising the crust. The new model will be employed to calculate the equation of state and the composition of the crust, and applied to predict properties that are important for neutron-star (global) modelling.
Variety of nuclear shapes in 96Zr studied with AGATA and GRIFFIN gamma-ray spectrometers

SL-DRF-24-0294

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Magdalena Zielinska

Starting date : 01-10-2024

Contact :

Magdalena Zielinska
CEA - DRF/IRFU/DPhN/LENA

01 69 08 74 86

Thesis supervisor :

Magdalena Zielinska
CEA - DRF/IRFU/DPhN/LENA

01 69 08 74 86

Laboratory link : https://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=483

More : https://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=790

The thesis will focus on the experimental study of the nuulear properties of the heaviest stable zirconium isotope (96Zr).
Recently, observation of a low-lying deformed state in this magic nucleus has been explained by a reorganization of nuclear shells in function of their occupation by protons and neutrons. These sophisticated nuclear-structure calculations predict a variety of shapes, both ellipsoidal and pear-like, to appear at low excitation energy in the 96Zr nucleus. We will investigate them using the powerful Coulomb-excitation technique, which is the most direct method to determine the shapes of nuclei in their excited states. The experiment will be performed using AGATA, a new-generation gamma-ray spectrometer, consisting of a large number of finely segmented germanium crystals, which allows us to identify each point where a gamma ray interacts with the detector material and then, using the so-called “gamma-ray tracking” concept, to reconstruct the energies of all emitted gamma rays and their angles of emission with highest precision. A complementary measurement will be performed at TRIUMF (Vancouver, Canada) using the world’s leading setup for beta-decay measurements called GRIFFIN. This project is a part of an extensive experimental program on shape coexistence and evolution of nuclear shapes undertaken by our group.
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.
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.
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.

High-precision measurements of nuclear recoil on the 100 eV scale for cryogenic detectors

SL-DRF-24-0274

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire etudes et applications des reactions nucleaires (LEARN) (LEARN)

Saclay

Contact :

Loïc THULLIEZ

David LHUILLIER

Starting date : 01-10-2024

Contact :

Loïc THULLIEZ
CEA - DRF/IRFU/DPhN/LEARN

0169087453

Thesis supervisor :

David LHUILLIER
CEA - DRF/IRFU/DPHN/LEARN

01 69 08 94 97

The CRAB method aims to provide an absolute calibration of cryogenic detectors used in dark matter and coherent neutrino scattering experiments. These experiments have in common the fact that the signal they are looking for is a very low-energy nuclear recoil (around 100 eV), requiring detectors with a resolution of a few eV and a threshold of O(10eV). Until now, however, it has been very difficult to produce nuclear recoils of known energy to characterize the response of these detectors. The main idea of the CRAB method, detailed here [1, 2], is to induce a nuclear capture reaction with thermal neutrons (25 meV energy) on the nuclei constituent the cryogenic detector. The resulting compound nucleus has a well-known excitation energy, the neutron separation energy, being between 5 and 8 MeV, depending on the isotope. If it de-excites by emitting a single gamma ray, the nucleus will recoil with an energy that is perfectly known, given by the two-body kinematics. A calibration peak, in the desired range of some 100 eV, then appears in the energy spectrum of the cryogenic detector. A first measurement performed in 2022 with a CaWO4 cryogenic detector from the NUCLEUS experiment (a coherent neutrino scattering experiment supported by TU-Munich, in which CEA is heavily involved) has validated the method [3].

This thesis comes within the scope of the second phase of the project, which involves high precision measurements using a thermal neutron beam from the TRIGA-Mark-II reactor in Vienna (TU-Wien, Austria). Two complementary approaches will be used simultaneously to achieve a high precision: 1/ the configuration of the cryogenic detector will be optimized for very good energy resolution, 2/ large crystals of BaF2 and BGO will be placed around the cryostat for a coincident detection of the nuclear recoil in the cryogenic detector and the gamma ray that induced this recoil. This coincidence method will significantly reduce the background noise and will enable the CRAB method to be extended to a wider energy range and to the constituent materials of most cryogenic detectors. We expect these measurements to provide a unique characterization of the response of cryogenic detectors, in an energy range of interest for the search for light dark matter and coherent neutrino scattering. High precision will also open up a window of sensitivity to fine effects coupling nuclear physics (nucleus de-excitation time) and solid-state physics (nucleus recoil time in matter, creation of crystal defects during nucleus recoil) [4].

The PhD student will be heavily involved in all aspects of the experiment: simulation, on-site installation, analysis and interpretation of the results.
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.
Lambda hyperon polarization measurement in exclusive deeply virtual meson production processes

SL-DRF-24-0386

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire structure du nucléon (LSN) (LSN)

Saclay

Contact :

Francesco BOSSU

Starting date : 01-10-2024

Contact :

Francesco BOSSU
CEA - DRF/IRFU/SPhN


Thesis supervisor :

Francesco BOSSU
CEA - DRF/IRFU/SPhN


This thesis focuses on measuring the polarization of Lambda hyperons in exclusive deeply virtual meson production processes. The study is rooted in a surprising discovery from the 1970s: in proton-Beryllium collisions, ? hyperons exhibited transverse polarization, challenging the predictions of perturbative Quantum Chromodynamics. Similar polarizations have since been observed in various collision systems.
The proposed research topic leverages deeply virtual exclusive reactions in electron-proton scattering, providing precise control over final states and initial particle polarizations. Specifically, the reaction e+p->e+Lambda+K+ is explored to shed light on the Lambda hyperon's polarization. This process is also sensitive to the poorly known transversity Generalized Parton Distributions (GPDs) of the nucleon, offering valuable insights into nucleon properties.
The thesis aims to analyze data collected with the CLAS12 experiment at the Jefferson Laboratory (JLab) in US, with a focus on e-p collisions with a longitudinally polarized NH3 target. Machine learning algorithms and simulations will be employed to enhance data reconstruction and event candidate selection. The candidate will also contribute to simulation studies for future detectors and their reconstruction algorithms for the EIC.
The research will be conducted within the Laboratory of Nucleon Structure at CEA/Irfu. A background in particle physics, computer science (C++, Python), and knowledge of particle detectors is beneficial for active participation in data analysis.
The student will have the opportunity to collaborate with local and international researchers, to participate in the CLAS collaboration, to join the EIC user group with frequent trips to the USA for data collection and workshops, and present research findings at international conferences.
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.

Drell-Yan production measurement in proton-proton collisions and preequilibrium dilepton production in heavy-ion collisions with the LHCb experiment at the LHC

SL-DRF-24-0277

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire plasma de quarks et gluons (LQGP) (LQGP)

Saclay

Contact :

Michael Winn

Starting date : 01-10-2024

Contact :

Michael Winn
CEA - DRF/IRFU/DPhN/ALICE

+33 1 69 08 55 86

Thesis supervisor :

Michael Winn
CEA - DRF/IRFU/DPhN/ALICE

+33 1 69 08 55 86

At the Large Hadron Collider (LHC) at Geneva, collisions of lead nuclei are used to create a thermodynamic system described by fluid dynamics under extreme conditions. The temperature of the short-lived system is sufficiently large in order to release the building blocks of matter at a subnucleonic scale, quarks and gluons. This state of matter is commonly called Quark Gluon Plasma (QGP). The space-time evolution of heavy-ion collisions at the LHC is described by close-to-ideal hydrodynamics after a short lapse of time. However, key features of the early stages of these collisions are largely unknown. These characteristics are crucial to understand the applicability limits of hydrodynamics and to understand thermalisation of a strongly interacting system.
In recent publications, it was pointed out that the dilepton production in the intermediate mass scale between 1.5 and 5 GeV/c² is highly sensitive to the ´thermalisation´ time scale towards the equilibrium QGP.

In addition, the LHC provides highly energetic proton and heavy-ion beams. They allow us to access the hadronic structure of the projectiles at very small fractional longitudinal momenta and at the same time still relatively large four momentum transfers. This configuration enables hence for perturbative calculations allowing the extraction of hadron structure information at very small fractional longitudinal momenta.
The theoretically best understood process in hadronic collisions is the production of dilepton pairs, the so-called Drell-Yan process. However, so far, no measurement down to 3 GeV/c² at a hadron collider has been published despite its theoretical motivation to test the lowest fractional momenta. In fact, at masses below around 30 GeV/c², semileptonic decays from heavy-flavour hadron decays start to dominate the dilepton production. This process has obscured any attempt to extract dilepton production in this kinematic domain.

The first goal of the thesis is the first measurement of Drell-Yan dimuons at low invariant masses at the LHC in proton-proton collisions that will be taken in 2024. This measurement will be based on novel background rejection techniques exploiting the forward geometry of LHCb. In a second part, the feasibility of the measurement in heavy-ion collisions will be investigated in the present and the future LHCb set-up. Depending on the outcome of the studies, a measurement in heavy-ion collisions will be conducted.
Study of the first Xenon-136 double-beta decay events of the PandaX-III experiment with neural network techniques

SL-DRF-24-0392

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire structure du nucléon (LSN) (LSN)

Saclay

Contact :

Damien NEYRET

Starting date : 01-10-2024

Contact :

Damien NEYRET
CEA - DRF/IRFU/DPhN/LSN

01 69 08 75 52

Thesis supervisor :

Damien NEYRET
CEA - DRF/IRFU/DPhN/LSN

01 69 08 75 52

More : https://pandax.sjtu.edu.cn/

The PandaX-III collaboration proposes to determine whether the neutrino is a Majorana particle, i.e. its own antiparticle. In this purpose this international collaboration, in which the Research Institute on Fundamental laws of the Universe (IRFU) of CEA Saclay participates, aims to observe neutrinoless double-beta decays of the Xenon-136, where the emission of the two electrons is not compensated by the simultaneous emission of two anti-neutrinos. Such an observation would violate the principle of conservation of leptonic number, in opposition with the predictions of the standard model of particle physics. The search of such rare events requires an enormous quantity of Xenon-136 atoms, a deep underground laboratory protected from cosmic rays and with low radioactive levels, like the Jinping underground laboratory (CJPL, Sichuan province, China), and a very effective particle detector.

The first phase of the experiment aims to construct a first TPC module (Time Projection Chamber) of 145kg of Xenon-136, which will be followed in a second stage by four other 200kg modules. The TPC will be equipped with detectors able to measure the energy of the two beta electrons with an excellent accuracy. The first TPC module will be commissioned end of 2024. The trajectory of the two electrons emitted by the double-beta decay will be reconstructed to measure the initial energy of those electrons, and to recognize the topology of their trajectories to differentiate them from gamma backgrounds which emit only one electron. That module will be equipped with gaseous Micromegas detectors which have a good energy resolution and a very good radio-purity which limits the amount of gamma backgrounds coming from radioactive contamination.

The PandaX-III collaboration is working on the construction of the first TPC module. It will be installed at CJPL during the year 2024. Reconstruction algorithms of detector data using neural networks are being developed, in order to complete the analytical methods already implemented in the REST environment of data reconstruction and analysis, to optimize double-beta events versus gamma backgrounds discrimination, and to improve the quality of the electron energy reconstruction. These algorithms are trained and evaluated on simulated Monte-Carlo events. Data from reduced-size TPC prototype will be also used to test these algorithms in real conditions. As soon as the first module will be installed end of 2024 these algorithms will be used for detector calibrations and for being implemented in real data analysis. They will be then used to extract the first physics results on double-beta events.

The main task of the PhD student will be to contribute on the development of data reconstruction algorithms based on neural networks, in particular by taking into account the defects of the detectors (dead channels, performance inhomogeneity, gas impurities, etc...) and by implementing in REST the data correction methods needed to compensate these defects. That work will include studies of data from prototype TPC chambers, as well as Monte-Carlo simulations. Moreover, as soon as the data from the first TPC module will be available the student will participate to the data analysis and the extraction of the physics results. These studies will be presented in conferences and published in scientific journals. The student will also participate to an R&D to optimize Micromegas detectors in order to improve their energy resolution as well as their general performance in high pressure gaseous Xenon.

A Master internship of 4 to 6 months would be also possible in the IRFU/DPhN PandaX-III group before the start of the PhD thesis.
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.
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.
Towards a high spatial resolution pixel detector for particle identification: new detectors contribution to physics

SL-DRF-24-0706

Research field : Particle physics
Location :

Département d’Electronique, des Détecteurs et d’Informatique pour la physique (DEDIP)

DÉtecteurs: PHYsique et Simulation

Saclay

Contact :

Nicolas FOURCHES

Starting date : 01-09-2024

Contact :

Nicolas FOURCHES
CEA - DRF/IRFU

0169086164

Thesis supervisor :

Nicolas FOURCHES
CEA - DRF/IRFU

0169086164

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

Future experiments on linear colliders (e+e-) with low hadronic background require improvements in the spatial resolution of pixel vertex detectors to the micron range, in order to determine precisely the primary and secondary vertices for particles with a high transverse momentum. This kind of detector is set closest to the interaction point. This will provide the opportunity to make precision lifetime measurements of short-lived charged particles. We need to develop pixels arrays with a pixel dimension below the micron squared. The proposed technologies (DOTPIX: Quantum Dot Pixels) should give a significant advance in particle tracking and vertexing. Although the principle of these new devices has been already been studied in IRFU (see reference), this doctoral work should focus on the study of real devices which should then be fabricated using nanotechnologies in collaboration with other Institutes. This should require the use of simulation codes and the fabrication of test structures. Applications outside basics physics are X ray imaging and optimum resolution sensors for visible light holographic cameras.
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

Starting date : 01-10-2024

Contact :

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

0169086626

Thesis supervisor :

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

0169086626

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.
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.
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.
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.
Accessing the 3D structure of pions with CLAS12

SL-DRF-24-0328

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire structure du nucléon (LSN) (LSN)

Saclay

Contact :

Maxime DEFURNE

Damien NEYRET

Starting date : 01-10-2024

Contact :

Maxime DEFURNE
CEA - DRF/IRFU/DPhN/LSN

01 69 08 32 37

Thesis supervisor :

Damien NEYRET
CEA - DRF/IRFU/DPhN/LSN

01 69 08 75 52

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

In collaboration with the Thomas Jefferson Laboratory (JLab) in the USA, the researchers in the laboratory of nucleon structure at Irfu want to understand how quarks and gluons interact to form hadrons such protons, neutrons and pions. At JLab, a 11-GeV electron beam is impinged on a proton target. The protos are constituted of three quarks surrounded by a cloud of quark/antiquark pairs whose quantum numbers are similar to pions. The electrons of the beam will interact with these pairs with a structure analogous to a pion. More specifically, we are interested in the deeply virtual Compton scattering (DVCS) giving correlations between longitudinal momentum and transverse position of quarks in a pion. In other words, we are going to perform the very first 3D study of the pion structure. The PhD student will analyze data already available to isolate the DVCS events. A digital twins of the Monte-Carlo simulation/reconstruction chain will be produced with a conditional Generative Adversarial Network in order to caracterize faster and more accurately the background and, in the end, subtract it. The PhD student will travel two to three times a year to JLab, participating to the data taking as well as attending the collaboration meeting. The results will be presented in international conferences and published in peer-reviewed journals.
Bc meson production in the Pb-Pb collisions at 5.36 TeV of the LHC Run 3

SL-DRF-24-0364

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire plasma de quarks et gluons (LQGP) (LQGP)

Saclay

Contact :

Javier CASTILLO

Starting date : 01-10-2024

Contact :

Javier CASTILLO
CEA - DRF/IRFU/DPhN/LQGP

+33 169087255

Thesis supervisor :

Javier CASTILLO
CEA - DRF/IRFU/DPhN/LQGP

+33 169087255

Laboratory link : http://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=500

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

A few micro-seconds after the Big Bang, the Universe was in a quark gluon plasma (QGP) state. Such state is predicted by Quantum Chromodynamics, which is the theory of strong interactions, and should be reached at very high temperature or energy density. Such conditions are reproduced in ultra-relativistic heavy ion collisions at the LHC at CERN.
Among the various QGP observables, the study of hadrons with heavy-flavour quarks (charm c or beauty b) and quarkonia (c-cbar or b-bbar bound states) is particularly important to understand the properties of the QGP. Indeed, heavy quarks are produced by hard scatterings between partons of the incoming nuclei in the early stage of the collision, and thus experience the full dynamics of the collision.
Thanks to the measurements of J/psi (c-cbar) production in Pb-Pb collisions of Runs 1 and 2 of the LHC, the ALICE collaboration showed the existence of the regeneration mechanism: when the initial number of produced quark/anti-quark pairs is large and if heavy quarks do thermalise in the QGP, then new quarkonia could be produced in the QGP by recombination of heavy quarks. Other mechanisms, such as colour screening, could affect the production of quarkonia. Bc mesons are composed of a b quark and an antiquark c. Their production is therefore strongly disfavored in proton-proton collisions. In Pb-Pb collisions, instead, their production could be largely increased due to the regeneration mechanism.
We propose to study the production of Bc mesons in Pb-Pb collisions at a center-of-mass energy per nucleon pair (sqrt(sNN)) of 5.36 TeV at the LHC with the data of Run 3 (2022-2025). The ALICE apparatus was upgraded in view of LHC Runs 3 and 4 with, in particular, the addition of a silicon pixel tracker (MFT) that complements the ALICE forward spectrometer as well as new readout electronics for the latter. These upgrades will allow us to: Profit from the planned increase in luminosity of the LHC, thus tripling in one year the data collected in the full LHC Run 2 (2015-2018); Measure with high precision secondary vertices of b-hadron decays. The Bc mesons will be measured at forward rapidity by reconstructing three secondary muons with the muon spectrometer and the MFT of ALICE.
The student will first contribute to the optimization and characterization of the muon spectrometer and MFT matching algorithm and the secondary vertex reconstruction. Secondly, the student will study the production of Bc mesons in Pb-Pb collisions. Finally, the results will be compared with other experimental results as well as various theory calculations.
During this work the student will become familiar with the grid computing tools and the simulation, reconstruction and data analysis software of the ALICE Collaboration.
Olfactory technology (Qi - Wei): Chinese inspiration for ecotechnology

SL-DRF-24-0856

Research field : Various
Location :

DIR

Laboratoire de recherche sur les sciences de la matière

Saclay

Contact :

Vincent Bontems

Dominique LESTEL

Starting date : 01-10-2024

Contact :

Vincent Bontems
CEA - DRF/IRFU/LARSIM/LARSIM

0169087094

Thesis supervisor :

Dominique LESTEL
Ecole Normale Supérieure de Paris - Archives Husserl

0169087094

Personal web page : https://researchgate.net/profile/Vincent-Bontems

Laboratory link : https://i-i2i-personnes.intra.cea.fr/Person.aspx?accountname=INTRA%5Cvb216113

More : https://philosophie.ens.fr/-Lestel-Dominique,134-.html

The specificity of Chinese technological thought has been the subject of recurrent philosophical debate since the early 20th century. This discussion highlights the originality of the sensory relationship with nature expressed in Chinese writing and culture. “Olfactory technology (Qi - Wei): a Chinese inspiration for ecotechnology” explores the hypothesis that a philosophy of technology, inspired by China but open to other cultures, can renew thinking on technology in its relationship to the environment, based on the paradigm of olfaction (Wei).
This approach is based on an analysis of traditional Chinese thought developed by contemporary Chinese philosophers, in particular Gong Huanan, and shows its influence on current Chinese technological thought. It also draws on the work of specialists in olfaction, as well as Western philosophers of technology, science and the imaginary (such as Gilbert Simondon, Gaston Bachelard and Dominique Lestel).
The primary scientific challenge is to restore the olfactory paradigm of Chinese technological thought in order to examine its relationship to the environment, and then to develop a transcultural ecotechnological reflection. In the light of these analyses, we will then reconsider the imaginaries of robotic and digital technologies in order to explore new avenues of innovation. Finally, from a science fiction prototyping perspective, speculative fictions will extend the analysis by examining the impact of imaginable technologies based on the olfactory paradigm.

 

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