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59 sujets IRFU
• Accelerators physics
• Astroparticles
• Astrophysics
• Computer science and software
• Electromagnetism - Electrical engineering
• Electronics and microelectronics - Optoelectronics
• Health and environment technologies, medical devices
• Nuclear physics
• Numerical simulation
• Particle physics
• Radiation-matter interactions
• Solid state physics, surfaces and interfaces
• Theoretical Physics
• Thermal energy, combustion, flows
• Various
Unified theory of nuclear structure and reactions in the open quantum system framework
SL-DRF-22-0345
Département Grand Accélérateur National d'Ions Lourds
Grand Accélérateur National d'Ions Lourds
Marek PLOSZAJCZAK
Starting date : 01-01-2022
CEA - DRF/IRFU//GANIL
02 31 45 4590
Thesis supervisor :
Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2021/09/GSM-thesis2022.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.
FIssion Studies at VAMOS in Inverse Kinematics (FISVIK)
John David FRANKLAND
CNRS - GANIL/Grand Accélérateur National d'Ions Lourds
Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2021/09/FISVIK-thesis2022.pdf
The nuclear fission process is driven by a complex interplay between the dynamical evolution of a quantum system composed of a large number of nucleons and the intrinsic nuclear structure of the system at extreme deformations as well as heat flows. The balance between these various aspects decide the characteristics of the emerging fragments. Innovative experiments are conducted to widen our knowledge of fission, aiming notably at a complete identification and characterization of the fission fragments and the study of unstable fissioning systems. At GANIL, accelerated heavy fissioning system is excited through nuclear reactions and the VAMOS large-acceptance magnetic spectrometer is used to identify, in mass and nuclear charge, the full distribution of fragments while a silicon telescope used to detect the residual recoil emitted in the transfer reaction. The planned upgrade of the silicon detection system (PISTA) used to tag the fissionning systems produced by transfer reactions will result in an improved selectivity and precision of the formation condition of the fissioning system. The proposed thesis consists in the characterization of the PISTA detector that will be used with VAMOS for the study of fission yields with unprecedent precision in the regions of light actinides in the vicinity of Pb. These results will be both pertinent to fundamental science and nuclear data for next generation reactors.
Matter's Origin from RadioActivity: first experiments analysis
Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2021/09/MORA-FEA-thesis2022.pdf
The Matter's Origin from RadioActivity (MORA) project searches for a sign of CP violation in nuclear ? decay, via the precise measurement of the so-called D correlation. An innovative technique of in-trap ion polarization for such a measurement will enable to attain unprecedented sensitivity to New Physics, which could explain the matter-antimatter asymmetry observed in the universe. With a goal in sensitivity on a non-zero D of a few 10-5, MORA will be in particular probing LeptoQuarks Models, in a way which is presently being studied by theoreticians from IJCLab. The first experiments are being prepared at JYFL in Jyväskylä. Their goal is two-fold: the proof-of-principle of the in-trap polarization technique, and the demonstration of the precise measurement of the D correlation by a controlling the associated systematic effects. The goal of the PhD thesis is the data – analysis of these first experiments.
New Judicious Experiments for Dark sectors Investigations – First Experiment
François DE OLIVEIRA SANTOS
Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2021/11/NewJEDI-thesis2022.pdf
The PhD project consists on the data analysis of the first experiment of the New JEDI project, that will take place beginning of 2022 at Orsay. It aims to bring an alternative explanation to the Universe functioning: check the existence of an additional interaction between ordinary matter and hypothetical Dark Sectors particles of the Universe. The particle allowing the interaction is named Dark Boson. The experiment will allow in practice to check the existence or not of a few MeV mass boson and characterize it if so.
FISSION STUDIES WITH VAMOS++ AND FALSTAFF SPECTROMETERS
Diego RAMOS-DOVAL
Jean-Eric DUCRET
Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2021/09/FISFAS-thesis2022.pdf
The fission process is a violent reaction in which a heavy nucleus is split in two fission fragments. More than 300 different isotopes are produced from one fissioning system and their relative production is strongly determined by the nuclear structure along with the nuclear dynamics that drives the system from an initial state to the final break-up through different states of deformation.
Nowadays, the experimental access to the complete identification of fission fragments is still very challenging and this prevents a complete understanding of the fission process. The FALSTAFF spectrometer offers a new opportunity to identify fission fragments in terms of mass, nuclear charge and velocity vector.
The subject of this PhD is the study of the fission process of minor actinides produced in inverse kinematics. This experiment will benefit from the combined setup of FALSTAFF and VAMOS++ spectrometer in order to measure both fragments at the same time from different incoming channels, either fusion-fission or transfer-fission. The objectives of this PhD are two-fold: the full characterization of the FALSTAFF spectrometer, and the determination of isotopic fission-fragment yields and the scission configuration of exotic minor actinides.
Development of an X-ray detection system for particle ID of superheavy nuclei
Dieter ACKERMANN
Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2021/11/XSHN-thesis2022.pdf
The synthesis and study of the superheavy nuclei (SHN) is still one of the major challenges of modern nuclear physics. Experimental studies of hitherto unknown nuclei depend crucially on their identification in terms of atomic charge Z and nuclear mass A. To complete particle ID capabilities of the separator-spectrometer set-up S3 at GANIL-SPIRAL2, already providing a mass resolution sufficient to resolve the A of SHN, its focal plane detection system SIRIUS will be provided with X-ray detection for Z identification of the species of interest. The development of an X-ray detection system array, employing thin germanium crystals with thin entrance windows (based on so-called Low-Energy Photon Spectrometers (LEPS)), its integration in the SIRIUS set-up as well as its in-beam test and use for SHN decay spectroscopy will be the main tasks of the Ph.D. thesis. The Ph.D. student will be involved in SHN spectroscopic studies at GANIL and international accelerator laboratories like ANL or FLNR-JINR, which serve as efficient preparation of the experiment campaigns planned at S3 which is scheduled to come online in 2024. This Ph.D. thesis work is an important step for the preparation of the detection instrumentation needed for the S3 operation.
AI for cryogenics and RF of superconducting accelerators
ADNAN GHRIBI
CNRS -
Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2021/09/ACAS-thesis2022.pdf
SPIRAL2 is a heavy ions accelerator delivery some of the most intense beams in the world. Its heart, a superconducting LINear Accelerator (LINAC) relies on 26 superconducting resonator cavities cooled to -269ºC. The operation of SPIRAL2 faces challenges that go beyond the beam itself and extend to utilities like cryogenics and radiofrequency systems. In 2009, a joint R&D program between GANIL and CEA has led to the development of a thermodynamic model of the SPIRAL2 LINAC resulting in a model-based control of the cryogenic system. However, radiofrequency (RF) and cryogenics being heavily interlaced for a superconducting LINAC, the next step is to extend the existing model to radiofrequency dynamics. The other purpose of this PhD thesis is to tackle advanced fault detection for RF and cryogenics from the machine learning perspective.
Investigating the nature of Gamma-Ray Bursts using MXT on board the SVOM mission
Direction d'Astrophysique (DAP)
Laboratoire des spectro-Imageurs spatiaux (LISIS)
Diego GOTZ
CEA - DRF/IRFU/DAP/LISIS
+33-1-69-08-59-77
Personal web page : https://irfu.cea.fr/Pisp/diego.gotz/
Laboratory link : https://www.svom.eu
Gama-Ray Bursts (GRB) are short (up to few tens of seconds) and intense flashes of gamma-rays, appearing from random directions over the entire sky. The gamma-rays (and the later afterglow emission observed at other wavelenghts) are associated to shock accelerated particles within relativistic narrow jets of plasma. The jets are created by the collapse of very massive stars (more than 50 times the mass of the Sun) or the merging of two compact objects (e.g. two neutron stars).
SVOM (Space based Variable astronomical Object Monitor) is a Sino-French mission developed in collaboration by the French Space Agency (CNES) and the Chinese Academy of Science (CAS) and the Chinese National Space Administration (CNSA). It is planned for launch early 2023 for a nominal mission lifetime of three years.
It will carry on-board four instruments among which the Micro-channel X-ray Telescope (MXT), a focusing X-ray telescope with a field of view of about 1°x1°, sensitive in the 0.2-10 keV energy range. The successful PHD candidate will be part of the MXT science team and be in charge of analyzing MXT data, since the very beginning of the SVOM mission. X-ray afterglow data will be coupled to the multi wavelength data in order to build a clear phenomenological picture of the SVOM GRBs, and to understand GRB progenitors and radiation processes.
3-dimensional scintillation dosimetry for small irradiation fields control in protontherapy
Anne-Marie FRELIN-LABALME
Laboratory link : https://www.ganil-spiral2.eu/wp-content/uploads/2021/09/SCICOPRO-thesis2022.pdf
Radiotherapy is an important modality in treatment cancer. In this domain, proton beams have ballistic superiority against photon beams. Nevertheless, the use of protontherapy to treat small volume tumors (typically less than 27 cm3) is limited because of the lack of dosimetry tools adapted to small irradiation fields. To answer this issue, an innovative dosimetry system has been developed. It is based on a scintillating block of 10 × 10 × 10 cm3, a mirror and an ultra-fast camera recording the scintillation from different points of view. The system can be used to check proton beam characteristics (position, energy, intensity), or the dose distribution delivered by a treatment.
The system has already shown very good performance to measure beam characteristics and is very promising for 3-dimensional dosimetry
The objective of this PhD thesis will be to develop numerical methods to convert the scintillation maps into dose maps. This includes the study of the energy dependence of the scintillation yield with proton beams, methods of image treatment and calibration methods.
ADVANCED AND ARTIFICIAL INTELLIGENCE TECHNIQUES TO MITIGATE LINEAR AND NON-LINEAR IMPERFECTIONS IN FUTURE CIRCULAR COLLIDERS
Research field : Accelerators physics
Département des Accélérateurs, de Cryogénie et de Magnétisme (DACM)
Laboratoire d'Etudes et de Développements pour les Accélérateurs (LEDA)
Barbara Dalena
CEA - DRF/IRFU/DACM
Personal web page : http://dalena.web.cern.ch/dalena/
Laboratory link : http://irfu.cea.fr/dacm/index.php
After the discovery of the Higgs boson at the LHC, particle physics community is exploring and proposing next accelerators, to address the remaining open questions on the underlying mechanisms and on the constituents of the present universe. One of the studied possibilities is FCC (Future Circular Collider), a 100-km-long collider at CERN. The hadron version of FCC (FCC-hh) seems to be the only approach to reach energy levels far beyond the range of the LHC, in the coming decades, providing direct access to new particles with masses up to tens of TeV. The electron version of FCC brings a tremendous increase of production rates for phenomena in the sub-TeV mass range, making precision physics studies possible. A first study has shown no major showstopper in the colliders' feasibility but has identified several specific challenges for the beam dynamics: large circumference (civil engineering constraints), beam stability with high current, the small geometric emittance, unprecedented collision energy and luminosity, the huge amount of energy stored in the beam, large synchrotron radiation power, plus the injection scenarios. This thesis will focus on the optimization of the hadron option of the future circular collider against linear and non-linear imperfections (i.e. magnets alignments and their field quality). A key point of this thesis is the comparison of current advanced correction schemes to techniques based on machine learning. The application of these techniques to accelerators is one of current hot topics in the field and pursued worldwide.
Dark matter search and the Galactic Center in very-high-energy gamma rays with H.E.S.S.
Research field : Astroparticles
Service de Physique des Particules (DPHP)
Groupe Astroparticules (GAP)
Emmanuel MOULIN
CEA - DRF/IRFU/DPhP/HESS 2
Personal web page : http://irfu.cea.fr/Pisp/emmanuel.moulin/
Laboratory link : http://irfu.cea.fr/dphp/Phocea/Vie_des_labos/Ast/ast_sstheme.php?id_ast=28&id_unit=8
More : https://www.mpi-hd.mpg.de/hfm/HESS/
The PhD thesis will be focused on the analysis and interpretation of the observations carried out in the Galactic Centre region by the H.E.S.S. observatory over more than 15 years. The first part of the work will be devoted to the low-level analysis of the GC data and the study of the systematic uncertainties in the massive GC dataset. In the second part, the PhD student will combine the H.E.S.S.-I GC and H.E.S.S.-II IGS observations in order to search for DM signal using multi-template analysis techniques. The third part of the work will be dedicated to the development of a new analysis method to search for astrophysical signal using Bayesian neural networks and its implementation for the search of dark matter and source variability in the GC region. In addition, the PhD student will be involved in the data taking and data quality selection of H.E.S.S. observations.
Searches for counterparts to gravitational waves with H.E.S.S. and CTA
Fabian Schussler
CEA - DRF/IRFU
Personal web page : http://irfu.cea.fr/Pisp/fabian.schussler/index.html
Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=1025&voir=fm
More : https://astro-colibri.com
Over the last two years the Imaging Air Cherenkov Telescopes (IACTs) H.E.S.S. and MAGIC were able to detect very-high-energy gamma-ray emission from gamma-ray bursts (GRBs). These breakthrough results have triggered renewed discussions of the particle acceleration and emission mechanisms that can be found in these violent explosions [1].
Complementing the detections of GRBs via X-ray satellites, the detection of gravitational waves allows to provide new and complementary insights into the pre-explosion phase, the initial conditions, the geometry of the system, and much more. The proposed thesis project will exploit the exciting possibilities of combining the detection of GWs and the detection of the resulting GRB by VHE gamma-ray observatories in truly multi-messenger observations and analyses.
The core of the proposed project will be H.E.S.S., currently the world's most sensitive gamma-ray instrument, and CTA, the next generation, global high-energy gamma-ray observatory. We'll also collaborate closely with partners from around the world including obviously the gravitational wave instrument Advanced VIRGO, the SVOM satellite to detect GRBs, various radio telescopes in Australia and South Africa, optical observatories, and many more. The group at IRFU, CEA Paris-Saclay is leading observations of transient phenomena by both H.E.S.S. and CTA and has long-standing experience with these challenging observations. The group is also driving changes and modernizations of the communication in the astroparticle community (e.g. via the Astro-COLIBRI web/smartphone application, [2]).
The PhD student will first have the opportunity to participate in the development and improvement of the framework that allows to optimize the schedule of follow-up observations of astrophysical transients. Some of the most interesting event are being detected only with large localization uncertainties (i.e. especially GWs, but also GRBs, neutrinos and others). We therefore need specialized tools and algorithms that allow to point the follow-up instruments like H.E.S.S. into the right direction to rapidly catch the associated emission [3]. A crucial observation period by the GW interferometers (called O4) is scheduled to start end of 2022. This timing is perfectly matching the PhD project presented here, as the selected student will have the opportunity to lead the H.E.S.S. and CTA/LST-1 follow-up observations searching for GRBs and other VHE gamma-ray counterparts to the GWs detected by LIGO/VIRGO/KAGRA during that period. A sizeable amount of observation time with both the H.E.S.S. and CTA/SLT-1 IACTs has been reserved for these exciting searches. We'll thus have ample opportunities to optimize our follow-up procedures, lots of data to analyze, results to present at international conferences, and papers to publish.
The core of the proposed thesis project will be the real-time search for transient high-energy gamma-ray emission linked to the detection of a gravitational wave (and other multi-messenger astrophysical transients like high-energy neutrinos, gamma-ray bursts, fast radio bursts, stellar/nova explosions, etc.). The combined observations will unequivocally prove the existence of a high-energy cosmic ray accelerator related to these violent multi-messenger phenomena and will allow to derive novel insights into the most violent explosion in the universe.
[1] H.E.S.S. Collaboration: "Revealing x-ray and gamma ray temporal and spectral similarities in the GRB 190829A afterglow, Science, Vol. 372 (2021);
[3] P. Reichherzer, F. Schüssler, et al. : "Astro-COLIBRI-The COincidence LIBrary for Real-time Inquiry for Multimessenger Astrophysics", ApJS 256 (2021);
[2] H. Ashkar, F. Schüssler, et al. : "The H.E.S.S. gravitational wave rapid follow-up program", JCAP 03 (2021);
Study of accretion and ejection processes in variable black hole systems with SVOM
Research field : Astrophysics
Laboratoire d'Etudes des Phénomènes Cosmiques de Haute Energie (LEPCHE)
Andrea GOLDWURM
CEA - DRF/IRFU/DAp/LEPCHE
Laboratory link : https://irfu.cea.fr/dap/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=974
More : https://apc.u-paris.fr/APC_CS/fr
We propose to carry out a study of accretion and ejection processes in black hole systems which are highly variable or transient emitters of high energy photons, by using the multi-wavelength data of the SVOM space mission and the relevant multi-messenger data that will be available to our laboratory.
The super-massive black holes located in galaxy centers, in particular those that generate the luminous Active Galactic Nuclei (AGN), or the stellar-mass black holes that evolve in bright X-ray close binary systems (XRB), show a high-energy emission (in X and gamma-rays) which is always variable and often transient. They will be priority targets for the Chinese-French space mission SVOM dedicated to the variable high-energy sky and that will be launched early 2023. SVOM will provide a large set of data from optical to gamma-ray wavelengths of high energy sources particularly those located at high galactic latitudes during the observations of the General Program (GP) of the mission. Galactic sources will be pointed instead mainly during Target of Opportunity (ToO) observations triggered by the appearance in the sky of a new transient source, for example of a BH X-ray Nova. APC has important responsibilities in these programs and it will be at the center of the scientific projects that will exploit these data. The thesis will focus on those programs dedicated to analysis and astrophysical interpretation of the mission data on BH systems, and will profit of, and contribute to, the large expertise in X/gamma-ray data analysis and in astrophysics of compact objects of the team. Particular attention will be dedicated to the multi-messenger astronomy context of the BH observations, with the search for possible neutrino, cosmic ray and gravitational wave emissions associated to the studied variable high-energy electromagnetic events.
Cross-correlating Euclid and DESI to probe the dark-matter - baryon connection in the cosmic web using weak gravitational lensing
Laboratoire CosmoStat (LCS)
Martin Kilbinger
CEA - DRF/IRFU/DAP/LCS
Personal web page : http://www.cosmostat.org/people/kilbinger
Laboratory link : http://www.cosmostat.org/
Weak gravitational lensing, the distortion of images of high-redshift galaxies due to foreground matter structures on large scales, is one of the most promising tools of cosmology to map the dark-matter distribution in the Universe. By combining weak lensing observations with foreground galaxy samples, we can measure the connection between dark matter and baryonic mass in galaxies. The lensing - galaxy cross-correlation is one of the main blocks in modern cosmology. It is an ingredient to test a variety of models of modified gravity, in which photons from weak lensing and galaxies experience different gravitational potentials. It further allows to measure two of the most important astrophysical uncertainties in cosmology, the intrinsic alignments of galaxies and galaxy bias.
The goal of this PhD thesis is to measure cross-correlations between weak lensing and galaxies, using the upcoming Euclid and DESI surveys. In preparation, existing weak-lensing data will be used from UNIONS, an ongoing imaging survey covering 3,600 square degree to date. This data will be cross-correlated with existing BOSS/eBOSS spectroscopic galaxies. This work aims toward a better understanding of the dark-matter – baryon connection, which will not only help to improve cosmological analyses, but also deepen our knowledge of how galaxies formed in their dark-matter environments in the early Universe.
The connection between morphology and star-formation activity in distant compact galaxies
Laboratoire de Cosmologie et d'Evolution des Galaxies (LCEG)
Emanuele DADDI
CEA - DRF/IRFU/DAP/LCEG
The formation and evolution of high-redshift massive galaxies is a hotspot in extra-galactic astronomy. In the study of the growth of galaxies it is crucial to investigate both the evolution in the physical scale (i.e., morphology) as well as in stellar mass, with redshfit. A special and important class of high redshift galaxies has been found recently, characterised by high surface density of stellar mass, that is, massive compact galaxies. From observations, there are two different categories for high-redshift compact galaxies: compact star-forming galaxies (cSFGs, also called 'blue nuggets'), and compact quiescent galaxies (cQGs, also called 'red nuggets'). Unlike what found in the local universe, massive compact galaxies are ubiquitous during early epochs.
The aim of this thesis, carried out by the candidate at the University of Nanjing, is to understand how compact massive galaxies form and evolve, and what causes the redshift evolution of their number density.
The candidate, Ms. Shiying LU, will pass two years in Saclay funded by a CSC bourse to work at her PhD project in collaboration with E. Daddi's group in LCEG. In this framework she will extend her research with the participation to surveys using the soon-to-be-launched JWST observatory and also explore forming cluster environments.
Intergalactic magnetic field and gamma ray bursts with CTA
Renaud Belmont
Thierry STOLARCZYK
Université de Paris (Paris 7) - DRF/IRFU/DAP/LEPCHE
Personal web page : http://irfu.cea.fr/Pisp/thierry.stolarczyk/
Laboratory link : http://irfu.cea.fr/en/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3709
More : http://www.cta-observatory.org/
The intergalactic magnetic field pervading the cosmic voids is suspected to be a relic field originating from the very first epoch of the cosmic history. The goal of this PhD is to look for signatures of this field in the high-energy data of gamma-ray bursts, and to predict the ability of the future CTA observatory to constrain its properties. This work combines both theoretical modelling and analysis of simulated CTA data.
Measurement of the small-scale Lyman-alpha forest with the DESI survey: looking for dark matter and neutrinos.
Groupe Cosmologie (GCOSMO)
Eric Armengaud
Guillaume Mention
CEA - DRF/IRFU/DPhP
Laboratory link : https://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=3428
More : https://www.desi.lbl.gov
The matter distribution on cosmological scales can be predicted within the standard cosmological model. It depends among others on the (yet unknown) absolute neutrino mass and on the properties of dark matter, whose nature is a great scientific mystery. The IRFU-DPhP cosmology team, gathering around 10 permanent researchers, is strongly involved in the DESI sky survey (Dark Energy Spectroscopic Instrument). DESI is the first among next-generation projects whose goal is to map large scale structures in the Universe. The DESI telescope, located in Arizona, started its observations in 2021 and will provide in the coming years an unprecedented 3D map of the Universe.
This thesis proposes to analyze and interpret DESI observations of the so-called Lyman-alpha forest, which measures the absorption by the intergalactic medium of light from distant quasars located at redshifts z ~ 2 - 4. Lyman-alpha observations provide the only measurement of the matter distribution both at "small" cosmological scales (~megaparsec), and in the early Universe (10 - 12 billion years ago, just 2 billion years after the Big Bang).
The PhD student will participate in the analysis of the complete DESI-Y1 ("Year-1") to Y3 Lyman-alpha forest data. He/she will improve our understanding of instrumental and astrophysical effects that are crucial for this observation. We propose that the student develops an original method to recover the full 3D statistical power spectrum of matter fluctuations from the 1D Lyman-alpha forest data, using tomographic reconstruction techniques already pioneered by the group.
In a second part of the thesis, the student will interpret the Lyman-alpha data to measure the properties of dark matter and neutrinos. The intensity and slope of the Lyman-alpha power spectrum depend in particular on the sum of neutrino masses. They also depend on other cosmological parameters, so that to break degeneracies, Lyman-alpha data will be combined with Cosmic Microwave Background (CMB) measurements. Currently the CMB+Lyman-alpha already bound the neutrino mass to be less than ~110 milli-eV (the best upper bound), while particle physics tells us it should be 60 milli-eV or more. With improved measurements and data combinations we therefore expect to get closer to a first detection. This work will be based on dedicated sets of cosmological simulations which are run at HPC infrastructures. Depending on his/her affinities, the student may use machine learning algorithms to optimize the exploitation of these simulations in order to infer cosmological parameters from the data.
Measuring the growth of massive structures in the distant Universe with deep multi-wavelength surveys
A growing convergence of research lines point to the first massive structures, like groups and clusters, assembling in the distant Universe as rosetta-stones to try to unveil important unsolved questions in galaxy and structures formation and evolution. This includes understanding the physical processes by which galaxies are fuelled by gas (which allows them to form their stars), by which galaxies change their structures, the role played by galaxy mergers, the feedback with their internal growing black holes, and interactions and the paths through which they eventually stop forming stars.
We propose a PhD project in which the student will participate to this research within a large international consortium that is leading large observational program of distant groups and clusters. Primarily the PhD student will be involved in using data from a recently awarded large program with the NOEMA interferometer that will use 159 hours of observations to discovery (confirm) and study 40 groups and clusters at 2<3.5. Additional observations from space and ground-based facilities will also be used. Key science goals will include: 1) the estimate of the evolving number densities of these structures and comparison to theoretic models as a strong constrain to structure formation theory and baryon assembly; 2) the measurement of the statistical modulation of star formation activity in these environments as a test of cold accretion theories; 3) the measurement of the statistical progression of quenching as a function of structure mass and redshift, as a powerful test of quenching mechanisms.
This thesis will potentially provide a solid formation for the student in many aspects of observational cosmology, from observations at one of the best ground-based telescopes to data analysis and interpretation all the way possibly to modeling, based also on the interests of the students and on results.
Simulating and optimising (sub-)millimetre observations for cosmology and interstellar medium science
Laboratoire d'études de la formation des étoiles et du milieu interstellaire
Marc SAUVAGE
CEA - DSM/IRFU/SAp/LFEMI
Laboratory link : https://irfu.cea.fr/dap/index.php
The wavelength range from millimeter to submillimeter is the preferred domain for the observation of the cold universe (interstellar medium) and the distant universe (microwave cosmological background, first galaxies). Following the success of the Herschel and Planck space missions, future space and ground-based observatories in this wavelength range are under study and are among the priorities of NASA and ESA programs for the coming decades. Scientific objectives range from the study of the primordial universe and the formation of high spectral shift structures to the role of the magnetic field in structuring the interstellar medium and star formation in our own galaxy. The optimization of mission concepts, from the required instrumental performances to the observation and data analysis strategies, requires the realization of simulations of the measurements of these future missions. The objective of the thesis will be to model these measurements and to develop a flexible simulation tool, applicable to different instrument and mission concepts. This tool will be used to inform the preparation of future observing missions in the millimeter and sub-millimeter range. This work will interface with a model of microwave sky emission (developed elsewhere), and with a study of the characteristics and imperfections of detectors developed at DAp for these future missions. A strong interaction with the research groups on the interstellar medium and the cosmic microwave background is also planned in order to understand the instrumental needs of these fields
Study of quasar clustering at all scales in DESI
Christophe YECHE
CEA - DRF/IRFU/SPP/Bao
Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=3428
The Large Scale Structures (LSS) of the Universe come from the growth, under the effect of gravitation, of small primordial fluctuations of density created by inflation. The measurement of the statistical properties of LSS allow us to study the inflation at very large scales (~Gpc), the Dark Energy at smaller scales (~100 Mpc) with Baryonic Acoustic Oscillations (BAO) and the gravity at even smaller scales (~tens of Mpc) with Redshift Space Distortions (RSD).
Our strategy for studying the LSS is to use a spectroscopic survey, DESI that will observe tens of millions of galaxies and quasars. The observations take place at the 4-meter Mayall telescope in Arizona .Since spring 2021, the project has started an uninterrupted observation period that will last 5 years and that will cover a quarter of the sky.
For this PhD, LSS are measured with a single tracer of the matter: the quasars, very distant and very luminous objects. This tracer allows us to cover a wide redshift range from 0.9 to 3.5 and to the Universe clustering at all scales, from a few tens of Mpc to Gpc.
During the first year, the PhD student will participate in the analysis of the first observation year (from spring 2021 to spring 2022). The PhD student will be able to devote to a global measurement of the cosmological parameters which will simultaneously cover all the scales. The thesis will end with the study of the first three years of observation of DESI.
New insights into radiative transfer modelling of exoplanet atmospheres
Laboratoire de dynamique des étoiles des (Exo) planètes et de leur environnement (LDE3)
Antonio Garcia Muñoz
CEA - DRF
Personal web page : http://antoniogarciamunoz.wordpress.com/
Laboratory link : https://irfu.cea.fr/dap/LDEE/index.php
More : https://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=971
With ~5,000 exoplanets known (http://exoplanet.eu), it is clear that the observed diversity of exoplanets is linked to their histories. In this setting, exoplanet science is faced with two key questions. The first one is how evolution may have modified the planets' bulk compositions. The question is timely as various facilities (JWST, launch date: December 2021; ARIEL, launch in 2028; E-ELT: first light in 2027) will study in unprecedented detail the atmospheres of exoplanets with spectroscopy. The second question is how evolution may have shaped the demographics of exoplanets. Notably, our grasp of demographics has changed radically in the last decade, and will continue evolving thanks to new discoveries from photometric space missions (e.g. TESS, PLATO) and radial velocity surveys on the main ground-based telescopes.
Digesting that empirical knowledge requires physically-motivated models that connect the properties of the planets and their host stars throughout their shared histories. To that end, our project will build a sophisticated treatment of radiative transfer (RT) for close-in exoplanets with both hydrogen- and non-hydrogen-dominated atmospheres. The RT modules will be implemented into the team's photochemical-hydrodynamic models to better understand the temporal evolution of the exoplanets. The predictions will help interpret the constraints that JWST will set on the composition of a few small exoplanets for which observing time has been granted as part of GTO+GO programs.
Study of the sources of gravitational waves with long duration of emission
Service de Physique Nucléaire (DPhN)
Groupe Théorie Hadronique
Hervé Moutarde
CEA - DRF/IRFU/SPhN/Théorie Hadronique
Personal web page : https://irfu.cea.fr/Pisp/herve.moutarde/
Laboratory link : https://irfu.cea.fr/en/Phocea/Vie_des_labos/Ast/ast_visu.php?id_ast=4698
More : https://www.elisascience.org/articles/lisa-consortium
Binary systems of stellar-mass black holes, such as those routinely detected since 2016 by the ground-based interferometers LIGO and Virgo, are among the sources of gravitational waves detectable by the Laser Interferometer Space Antenna (LISA) observatory. This space observatory will consist of three satellites 2.5 million kilometers apart and its launch is planned by ESA for 2034. This instrument will continuously capture a large number of distinct signals theoretically characterized to various degrees of accuracy, including : supermassive black hole binaries, galactic binaries, and binaries with very high mass ratios.
These last two types of sources and the binary systems of black holes of stellar masses share the characteristic of emitting for durations comparable to that of the LISA mission. They can produce very diverse signals and the observation of a large number of orbits can provide strong constraints on fundamental physics. In particular, precise measurements of the eccentricity of the orbits of binary black hole systems of stellar masses and of their spins should make it possible to discriminate the various scenarios of genesis of these systems.
As in any experiment, the actual data will be subject to a number of noises and artifacts, such as periods of data collection interruption. Taking these effects into account is essential to optimize the scientific potential of the mission
The main thread of the proposed work is a demonstration of scientific and technical capacity to process real data in a reliable and robust way. The diversity of the sources allows different studies of graduated difficulties but offering, each, an operational interest for the LISA mission. The methods established by the host team to treat galactic binaries will be used as a basis for the work devoted to other long-duration sources.
1.	Implementation in the software environment of the LISA mission of the waveforms associated with binary systems of black holes of stellar masses taking into account their eccentricities. Calculations from several formalisms are available and must be put in a form allowing precision and speed of execution.
2.	Study of the detection of such systems with LISA through the development of innovative algorithms. This step includes an evaluation phase of the performance of the algorithms.
3.	Determination of the source characteristics (signal-to-noise ratio, mass, redshift, etc.) allowing the measurement of the system eccentricity and discussion of the possible impact on LISA scientific objectives.
4.	Study of the impact of interruption periods in data acquisition (maintenance, subsystem instabilities, etc.) or of the presence of other gravitational wave sources in the frequency range considered.
This set of activities may however evolve according to theoretical advances, progress in LISA data analysis and the publication of new measurements by ground-based interferometers. All these activities can lead to constraints in the dimensioning of the mission, tools or methods of data processing.
This subject involves a significant amount of signal processing and careful programming, but requires a good understanding of the underlying physics. Its multidisciplinary aspect makes it possible to explore many fields depending on the scientific opportunities and the duration of a thesis
Understanding the evolution of galaxies with the James Webb Space Telescope
Benjamin MAGNELLI
David ELBAZ
The James Webb Space Telescope (JWST) will revolutionize our understanding of the evolution of galaxies in the so-called "cosmic noon" era. With its unparalleled angular resolution in the near- and mid-infrared window, it will measure the distributions of stars and dust-obscured star formation on the kpc scale, and reveal the presence of active dust-obscured supermassive black holes at their centers.
In the scenario so far favored to explain the evolution of galaxies and, in particular, the morphological transformation of spirals into ellipticals, it is the mergers of galaxies that destroy the disks and generate the spheroids. However, recent observations by our team have revealed the presence of compact star-forming nuclei in distant galaxies, supporting an alternative scenario in which they were built in situ, slowly and not abruptly.
This thesis will aim to distinguish these two scenarios of galaxy formation and morphological transformation by combining JWST/PRIMER/NIRCam images with HST/CANDELS/ACS images. Our team will have access to two major JWST cosmological programs, CEERS (PI. S.Finkelstein) and PRIMER (PI. J.Dunlop) whose data should arrive as early as June 2022 (or at the latest Dec.2022). We will perform a spatially resolved analysis of the spectral energy distribution of about 1200 galaxies which will allow, in particular, to determine their distribution of stars and star formation, decisive information to understand their origin and evolution.
Mapping physical parameters in supernova remnants assisted by machine learning
Fabio Acero
Spectro-imaging telescopes in X-rays allow to measure the position, Energy and time of arrival of every detected photon. Based on this photon list, one can construct data cube (x, y, energy) where a Spectrum can be obtained for each pixel. Despite the major progress from an instrumental point of view, the analysis methods in the X-ray community have stalled in the last decade and current methods will not be able to extract the full scientific potential of upcoming missions.
This project proposes to develop new analysis methods using advanced signal processing techniques based on the concept of sparsity and assisted by machine learning to map the physical parameters (temperature, metalicity, Redshift, etc) across extended sources such as supernova remnants or galaxy clusters.
Developing such methods will be key to tackle the issues of analyzing the very high spectral resolution data from next generation X-ray telescopes such as XRISM (2023) and Athena X-IFU (2034).
Characterization of magnetic activity cycles of the Sun a solar-like stars with data from SoHO, Kepler, and TESS satellites
Rafael A. Garcia
CEA - DRF/IRFU/DAP/LDE3
Laboratory link : https://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=971
The objective of this PhD is to better understand the magnetic activity of the solar-like stars using as a reference our Sun. These stars have and external convective envelope. The interaction of the convection, rotation and magnetic fields generate dynamo process that are at the origin of dynamos which generates magnetic activity cycles. Understanding this magnetic activity and the associated cycles is of the main importance to better understand the development of life as the one on Earth as well as to improve the detectability of exoplanets orbiting these active stars.
Impact of rotation and magnetism on the excitation of stellar oscillations: predictions for space asteroseismology
Stéphane MATHIS
Laboratory link : http://irfu.cea.fr/Sap/LDEE/index.php
From galactic to planetary systems' scales, stars are the elementary building blocks of our Universe. Their nucleosynthesis et their magneto-rotational dynamics drive their evolution and those of their environment. The unique observational method to probe their internal structure, rotation, and potentially magnetism is asteroseismology. Asteroseismology is the branch of astrophysics that studies the oscillations of stars. During the last decade, asteroseismology has revolutionised our understanding of the evolution, internal mixing, and rotation of stars and the characterisation of their planets. To be able to take advantage of all the power of asteroseismology it is mandatory to understand the excitation mechanisms (and the damping) of stellar oscillations. This is the key objective of this PhD project where we will study their stochastic excitation by turbulent stellar convective regions. The innovative aspect will be to take simultaneously the action of rotation and magnetism on the propagation of stellar oscillations and on the convective source that trigger them into account. This theoretical project is part of the scientific preparation of the M3 ESA space mission, which will be launched in 2026 in which CEA is highly involved.
Forward modelling of the galaxy density field in the DESI spectroscopic survey
Arnaud de Mattia
Vanina RUHLMANN-KLEIDER
CEA - DRF/IRFU/DPHP/GCOSMO
The goal of this PhD project is to develop a novel analysis pipeline to extract cosmological information from the wide galaxy redshift survey DESI (Dark Energy Spectroscopic Instrument), using numerical simulations and state-of-the-art machine learning and statistical inference techniques to overcome limitations of standard analyses.
DESI is a multi-object spectrograph mounted on the Mayall telescope at Kitt Peak, Arizona, which will enable redshift measurements of 35 millions of galaxies and quasars between 0.05 < z < 3.0, yielding a tenfold increase in statistics compared to previous spectroscopic surveys (e.g. BOSS, eBOSS). By the start of the PhD, the first year of DESI data taking, corresponding to one fifth of the total statistics will be completed, thereby constituting the largest spectroscopic dataset ever assembled. A threefold increase of this dataset is expected by the end of the PhD.
In this PhD we propose to develop a theoretically lossless approach to extracting cosmological information from galaxy surveys, in particular DESI, which consists in reproducing the observed galaxy density with simulations. Namely, an initial random dark matter density field is generated in a cubic box and evolved forward in time following the equations of gravity. The galaxy density field is then modelled on top of the simulated dark matter field and survey selection effects are applied. The likelihood of the observed galaxy density field given the simulated one is computed, and its value is used to iterate over, or to sample, initial conditions of the density field and cosmological parameters. This project, which may result in the first cosmological contraints from the galaxy forward modelling approach applied on real data, will lead to one or two first-author publications. It will also benefit greatly to the DESI standard analyses.
Cosmology from LiteBIRD and synergy with large-scale surveys like Euclid
Valeria Pettorino
Personal web page : https://www.cosmostat.org/people/valeria-pettorino
Laboratory link : https://www.cosmostat.org
More : https://www.valeriapettorino.com/
This PhD proposal is meant to combine information from galaxy surveys like the forthcoming Euclid space mission and Cosmic Microwave Background Experiments from ground and space.
The Cosmic Microwave Background radiation has demonstrated to be a powerful probe for cosmology: its temperature anisotropies carry information on the early-time Universe, as well as on the structure encountered along the light path. Measurements from balloons and detectors from ground are contributing to detail this picture with current data from Planck space mission, and forthcoming data from ground, balloons, and space.
Within galaxy surveys, ESA Euclid satellite , to be launched in 2023, will observe how galaxies formed to study the nature of dark energy and dark matter.
The PhD project is co-supervised by Valeria Pettorino (CEA/DRF/IRFU/DAp/LCS) and Dr. Stéphane Ilic (IJLAB, Orsay). We have identified three main goals:
1. contribute to the estimation of the scientific impact of LiteBIRD CMB space mission via forecasts;
2. contribute to the synergy between CMB experiments and Euclid within the Euclid likelihood development;
3. investigate different methods to separate foreground components and improve the reconstruction of the CMB signal.
Origin and nature of high-energy emission from microquasars: long-term behaviour and real-time monitoring with the INTEGRAL and SVOM observatories
Jérôme RODRIGUEZ
Impact of the density of galaxies in the analysis of the large spectroscopic survey DESI
Etienne Burtin
Over the last 30 years, the study of the Universe has led to the emergence of a standard model of cosmology based on general relativity. In this model, the Universe is made of ordinary matter, dark matter and a mysterious component called "dark energy", responsible for the recent acceleration of the expansion of the Universe. The large spectroscopic survey DESI, which has just started its 5-year observation campaign in the United States, aims to map the distribution of galaxies in the Universe 10 times more accurately than existing surveys. The scientific community is organizing itself to define the methods of data analysis in order to extract the maximum of information from these surveys and to enter the era of precision cosmology, in particular on the measurement of the growth rate of structures. This thesis proposes the original approach of using the large-scale matter density to significantly improve the precision of this measurement, in order to strengthen the tests of general relativity.
This thesis will take place at the Research Institute for the Fundamental Laws of the Universe at CEA-Saclay. The future PhD student will be integrated in the cosmology group of Irfu/DPhP, composed of 10 physicists and 4 PhD students. Present and driving force in the DESI experiment, the group also participates in Euclid and had in the past a strong contribution in SNLS, Planck and SDSS (BOSS and eBOSS), all experiments organized in international collaborations. The future PhD student will be integrated in the DESI collaboration and will analyze the data, benefiting from all the expertise of the group already acquired on BOSS and eBOSS.
Efficient AI algorithms for gamma spectrometry dedicated to field measurement
Research field : Computer science and software
Département d'Electronique, des Détecteurs et d'Informatique pour la physique (DEDIP)
Laboratoire ingénierie logicielle et applications spécifiques
Jérôme Bobin
Christophe BOBIN
CEA - DRF/IRFU/DEDIP/LILAS
CEA - DRT/DM2I/LNHB/LMA
Personal web page : http://www.jerome-bobin.fr
Gamma spectrometry analysis is a classic technique used for the identification and quantification of radionuclides in a radioactive source in strategic applications such as border surveillance, decommissioning, etc. Current analytical methods are based on spectral unmixing, using a library of characteristic spectra (spectral signatures), for each radionuclide to be identified. The case of field measurements on portable devices poses significant algorithmic challenges. On the one hand, the spectral signatures are fixed, severely limiting the robustness of the identification algorithms to the variability of the conditions of field measurements; the phenomena of attenuation or diffusion around a radioactive source lead to strong distortions of the measured spectra. On the other hand, both the small amount of data available to characterize the wide variety of measurable signatures in the field, and the use of portable devices require the development of machine learning algorithms. The objective of the thesis is the development of an algorithmic solution combining fast algorithms with a sober machine learning model, requiring little training data, for the joint estimation of activities and spectral signatures of the radionuclides to be identified. This solution will be developed so as to be implemented on a low-energy on-board digital system (FPGA). The thesis work will also focus on the assessment of the analysis performance balance (detection and identification) and energy sobriety.
Impact of the Mechanical Stress on the Training of High Field Superconducting Nb3Sn Magnets
Research field : Electromagnetism - Electrical engineering
Laboratoire d'Etudes des Aimants Supraconducteurs (LEAS)
Etienne Rochepault
Personal web page : https://www.researchgate.net/profile/Etienne-Rochepault
Laboratory link : https://irfu.cea.fr/dacm/index.php
More : https://home.cern/science/accelerators/future-circular-collider
In order to increase performances of future particle accelerators, high field superconducting electromagnets (higher than 10 T), based on Nb3Sn, are being developed. The LEAS at CEA Paris-Saclay is involved in several projects consisting in the design, manufacture and test of superconducting magnet demonstrators generating up to 16 T. The high fields and high currents (>10kA) required, generate high stresses on the conductor. The main problematic of these magnets is the sensitivity to external perturbations: the simple energy release can provoke the brutal transition of the superconductor to the resistive state. It is possible to bring the superconductor to a stable state using a "training", which consists in performing successive transitions in order to progressively modify the initial conditions. To do so, the stress state of the superconductor must be understood and mastered. The PhD student will lead the development and the setup of experiments aiming at studying the impact of the mechanical stress on the training of Nb3Sn magnets. In addition, the PhD student will be in charge of developing Finite Element Models which should allow the simulation of the training phase. This work should allow a better understanding and mastering of the phenomena in order to push forward the limits of Nb3Sn magnets.
DESIGN OF A NEW LOW POWER ANALOG TO DIGITAL CONVERTER FOR FUTURE SUBATOMIC PHYSICS EXPERIMENTS
Research field : Electronics and microelectronics - Optoelectronics
Systèmes Temps Réel, Electronique d'Acquisition et Microélectronique
Florent BOUYJOU
Damien NEYRET
CEA - DRF/IRFU/DEDIP/STREAM
CEA - DRF/IRFU/DPhN/LSN
Laboratory link : https://irfu.cea.fr/dedip/Phocea/Vie_des_labos/Ast/ast_service.php?id_unit=5&voir=groupe
In current and future high-energy physics experiments: LHC large detectors upgrades and experiments on future colliders, the granularity of particle detectors continues to increase and the use of multi-channel submicron integrated circuits has become a standard. Increasingly, signals from the detectors will have to be digitized by readout circuits and carried away from the experiment by ultra-fast links. The development of new fast and low-power analog-to-digital converters (ADC) operating in often extreme environments, in particular in terms of radiation, is a challenge. Located inside detectors, ADCs are subject to environmental constraints: temperature variations, aging and radiation. The trend has been to try to make the responses of these circuits as stable and independent as possible of variations in environmental parameters (T°, dose and time) and technological parameters (process variation and mismatch). Another approach is to establish precise calibration tables that can be "downloaded" into the generic ASIC as conditions change or generated automatically by the ASIC.
Design of a new readout circuit for highly dense hybrid detector
David Baudin
Olivier Limousin
CEA - DRF/DEDIP/STREAM
Laboratory link : https://irfu-i.cea.fr/dedip/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=3755
Our way to observe the sky have changed with the emergence of the multi-messenger astronomy. In order to efficiently detect electromagnetic counterparts of gravitational waves coming from the most compact objects, we need to develop new instruments pushing back limitations in sensitivity and angular resolution in the hard X-ray domain for a quick detection with low source confusion.
To follow progress in X-ray optics, new fine-pitch large area space detector systems shall be invented. In a similar way, the exploration of the solar system, whether for space weather or for the intensification of the Martian and Lunar exploration will benefit from miniature X/gamma-ray detectors.
Such a challenge has to be firstly solved at the level of the front-end electronics and its interconnects with sensors.
This thesis consists in the development of a new microelectronics circuit (ASIC) to be interconnected with a semiconductor detector (CdTe or Si). This circuit aims to be a matrix of 32 x 32 pixels with 250 x 250 µm² size each of them embedding a full charge readout system.
Since 2011 our team develops a new concept of hybrid detector called MC2 (Mini CdTe on Chip) which relies on 3D technologies such as WDoD (wireless die on die) and able to withstand the space environment. The ambition is to realize large focal plane with innovative spectro-imaging performance with time and polarimetry resolution for next X and gamma ray missions.
The targeted microelectronics technology is the XFAB 180 nm, particularly attractive for space missions thanks to its durable commercial and affordable availability. It constitutes a believable alternative to AMS 0.35 um widely used for space missions such as SVOM (ECLAIRs) and Solar Orbiter (STIX). On top of that, this technology has been migrated recently from Malaysia to France, an interesting perspective for the design optimization in the coming years.
Thanks to two PhD thesis, our group has designed two generations of circuits in this technology, which have shown promising results for the integration of self-triggered spectroscopic chain, with ultra-low noise and low power pixels of 250 x 250 µm². From a system point of view, these circuits have also shown the necessity to develop new blocks and to revise in depth front-end blocks to reach our ultimate low noise performances.
The objective of this thesis is to bring new solutions for a 2-side buttable large array circuit with 250 um pixel pitch, with an optimized modular architecture for its readout.
Optimization of the ClearMind detection module for the high resolution PET imaging
Research field : Health and environment technologies, medical devices
Groupe Santé et Energie (GSE)
Viatcheslav SHARYY
Personal web page : https://irfu.cea.fr/Pisp/viatcheslav.sharyy/
Laboratory link : https://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3730
Positron emission tomography (PET) is a nuclear imaging technique widely used in oncology and neurobiology research. The decay of the radioactive tracer emits positrons, which annihilate into two photons of 511 keV. Using time-of-flight technology, they can be used to reconstruct the point of annihilation and the distribution of 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 the microchannel plate. The induced electrical signals are amplified by gigahertz amplifiers and digitized by the fast acquisition modules SAMPIC. The time and coordinates of the gamma-conversion in the crystal are reconstructed using machine-learning techniques.
The candidate will work on characterization and optimization of the ClearMind detection module. This includes the measurement with pulsed laser and radioactive 22Na source, data analysis using ROOT/C++ software, reconstruction with machine-learning algorithms and interpretation with the help of Geant4 simulation.
The foreseen detector optimization will boost the TRL1 of the ClearMind technology from the level 2 to the level 5/6. It consists in improving the detection module design and thus in increasing the detection efficiency, in optimizing the high-speed read-out, and in improving the integration of the detection module with the digitizing electronics.
NEW PATHS FOR THE STUDY OF HEAVY NUCLEI
Research field : Nuclear physics
Laboratoire études du noyau atomique (LENA) (LENA)
barbara sulignano
Hunting for super heavy elements one of the most exciting and active topics during the last few years and has already produced new elements such as 113, 115, 117 and 118 in accelerator experiments. All these nuclei can be produced through fusion-evaporation reactions. However their studies are greatly hampered by the extremely low production rates, hence experimental information in this region is very scarce. The high-intensity stable beams of the superconducting linear accelerator of the SPIRAL2 facility at GANIL coupled with the Super Separator Spectrometer (S3) and a high-performance focal-plane spectrometer (SIRIUS) will open new horizons for the research in the domains of such rare nuclei and low cross-section phenomena at the limit of nuclear stability. The student will take an active part in the tests of the SIRIUS detector at GANIL.
Information on the heaviest elements have been obtained up to now via fusion evaporation reactions. It is however well known that the only nuclei one can reach using fusion-evaporation reactions are neutron deficient and moreover in a very limited number (because of the limited number of beam-target combinations). An alternative to fusion-evaporation could be a revolutionary method based on be deep-inelastic collisions. The student will take, therefore, an active part in the new scientific activities of the group having as primary aim the investigation of nuclear structure in the heavy elements using the new alternative method using multi-nucleon transfer reactions
First measurement of the pygmy resonance using neutron inelastic scattering at GANIL/NFS
Marine VANDEBROUCK
Diane DORÉ
The well-known giant dipole resonance, which corresponds to the oscillation of the neutron fluid against the proton fluid, is a broad resonance with a mean energy between 12 and 24 MeV. An additional dipole resonance has been observed at lower energy in neutron-rich nuclei, near the neutron separation threshold. This small-size structure, in comparison to the giant dipole resonance, is commonly known as the pygmy dipole resonance (PDR) and can be described as the oscillation of a neutron skin against a symmetric proton/neutron core. The PDR has been the subject of numerous studies, both experimental and theoretical. Indeed, the study of the PDR has raised a lot of interest since it can constrain the symmetry energy, an important ingredient of the equation of state which describes the matter in neutron stars. In addition, the enhancement of the dipole strength close to the neutron separation energy is expected to impact the astrophysical r-process (process that could explain the synthesis of heavy nuclei) by increasing the neutron capture rates. However, despite many experimental results, a consistent description of the PDR could not be extracted. In this context, we propose to study the PDR using a new experimental method: the neutron inelastic scattering. This new probe which is elementary from a nucleonic point of view and neutral, thus not influenced by the Coulomb interaction, is an original approach that will provide a new perspective on the nature of the PDR.
The LENA laboratory (Laboratoire d'Etude du Noyau Atomique), which belongs to the Nuclear Physics Department of IRFU, is strongly involved in the study of the structure of atomic nuclei. For many years, LENA researchers have been working in collaboration with teams from GANIL (France), GSI (Germany), the University of Jyväskylä (Finland)… where they conduct their experiments. The high intensity beams produced by GANIL-SPIRAL2, combined with the neutron beam production system available at NFS (Neutron For Science), allow since 2021 to produce neutron beams at the energy suited for inelastic scattering studies with unprecedented intensities.
The objective of the thesis is to study for the first time the pygmy resonance by inelastic neutron scattering. The thesis will consist of: i) participation in the experiment, ii) data analysis, and iii) interpretation of the results in collaboration with theorists.
Prompt and non-prompt quarkonium production in the Pb-Pb collisions at 5 TeV of the LHC Run 3
Laboratoire plasma de quarks et gluons (LQGP) (LQGP)
CEA - DRF/IRFU/DPhN/LQGP
Laboratory link : http://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=500
More : https://alice-collaboration.web.cern.ch
A few micro-seconds after the Big Bang, the Universe was in a quark gluon plasma (QGP) state. Such state is predicted by Quantum Chromodynamics, which is the theory of strong interactions, and should be reached at very high temperature or energy density. Such conditions are reproduced in ultra-relativistic heavy ion collisions at the LHC at CERN.
Among the various QGP observables, the study of hadrons with heavy-flavour quarks (charm c or beauty b) and quarkonia (c-cbar or b-bbar bound states) is particularly important to understand the properties of the QGP.
Quarkonia are rare and heavy particles which are produced in the initial stages of the collision even before the QGP is formed, mainly through gluon-fusion processes, and are therefore ideal probes of the QGP. As they traverse the QGP, the quark/anti-quarks pair will get screened by the many free quarks and gluons of the QGP. Quarkonia will then be suppressed by a colour screening mechanism in the QGP. Since the various quarkonium states have different binding energies, each state will have a different probability of being dissociated. This results in a sequential suppression pattern of the quarkonium states. Additionally, if the initial number of produced quark/anti-quark pairs is large and if heavy quarks do thermalise in the QGP, then new quarkonia could be produced in the QGP by recombination of heavy quarks. This mechanism is known as regeneration. At the LHC, Upsilon (b-bbar) and J/psi (c-cbar) are complementary. The former are thought to be more suited than to address the sequential suppression, while the latter should allow to study possible regeneration mechanisms. In addition, non-prompt J/psi, i.e. from weak decays hadrons containing one valance b quark, give access to the transport properties of b quarks in the QGP. More recently, photoproduction of J/psi has been observed in peripheral Pb-Pb collisions; J/psi are produced from the photon flux of the moving Pb ions mostly at very low transverse momenta. The characterization of these photoproduced quarkonia would allow to better constrain the initial state of the collisions as well as the properties of the QGP.
We propose to study the production of prompt and non-prompt quarkonia Pb-Pb collisions at a center-of-mass energy per nucleon pair (sqrt(sNN)) of 5 TeV at the LHC with the first data of Run 3 (2022-2024). An upgrade of the ALICE apparatus is ongoing with, in particular, the addition of silicon pixel tracker that will complement the ALICE forward spectrometer as well as new readout electronics for the latter. These upgrades will allow us to: Profit from the planned increase in luminosity of the LHC, thus tripling in one year the data collected in the full LHC Run 2 (2015-2018); Separate the prompt and non-prompt contributions thanks to the precise measurement of the quarkonium decay vertex into two muons.
The student will first develop the procedures to separate prompt and non-prompt quarkonia. In doing so, the student will thus contribute to the development of the new software for data reconstructions, simulation, calibration and analysis that the ALICE Collaboration is developing for Runs 3 and 4 of the LHC. Secondly, the student will study the production of prompt and non-prompt quarkonia in terms of production yields and azimuthal anisotropy. These studies could be performed as a function of the centrality of the collision and transverse momentum and rapidity of the quarkonia, for various types of quarkonia. Depending on the progress of the thesis work, these studies, which are a priority for quarkonia produced by the hadronic collision, could be extended to photoproduced quarkonia.
Study of anomalies in the production of fission fragments by the analysis of their prompt gamma rays
Laboratoire etudes et applications des reactions nucleaires (LEARN) (LEARN)
Thomas MATERNA
CEA - DRF/IRFU/DPhN/LEARN
Personal web page : https://www.researchgate.net/profile/Thomas_Materna
The analysis of prompt gamma rays emitted by fission fragments has become an essential tool for studying the nuclear fission process. It allows to probe the intrinsic properties of the fragments or to explore effects that are not yet well studied experimentally, such as the influence of the shape of the fragments on the fission process, the sharing of the excitation energy between the fragments or the distribution of the spins of the fragments just after the scission. On the other hand, the measurement of prompt gamma rays from fission provides useful nuclear data for reactor simulation.
The thesis work will consist in exploring the possibility of using prompt gamma rays to estimate the population of fragments - the independent fission yields - by comparing the values obtained by this method with evaluated yields, measured notably by mass spectrometry. The objective is to understand the anomalies, the important deficits in yields obtained via the prompt gamma cascade, which are encountered on several well-produced nuclei, by testing different hypothesis in the modeling of the fission process and of the de-excitation of the fission fragments. In a second step, the work will be to determine the yields of heavy fragments, rich in neutrons, for which the yields, obtained via the measurement of their delayed gamma, are uncertain.
The data on the thermal fission of U-235 and U-233 already measured by the FIPPS gamma spectrometer installed at the Grenoble research reactor and possibly the next measurements on FIPPS of the thermal fission of Cm-245 will be exploited to this purpose.
Charge exchange process and beta force function in the beta decay of fission products
Alain LETOURNEAU
Although known for more than 80 years, beta decay remains a very topical subject of study because it is at the heart of many applications where delayed processes are important, such as the delayed neutrons used to drive nuclear reactors or the residual power after transient phases of nuclear reactor operation. On the fundamental level, it plays a crucial role in the discovery and study of the properties of neutrinos from nuclear reactors.
In this thesis we propose to develop a phenomenological model of the beta force function that describes the process of charge exchange in the nucleus (a neutron becomes a proton). This model will have to integrate the maximum of known physics and will be able to rely on microscopic computational results. A first expectation of the work will be to use this model to generate a reference of unbiased electron and anti-neutrino energy spectra using the BESTIOLE code. This expectation will allow to study the origin of the reactor neutrino anomaly and will serve as a reference for current and future reactor neutrino experiments. A second expectation will be to implement this model in more advanced codes such as the neutron and gamma de-excitation code FIFRELIN. This will eventually allow the implementation of a tool for the treatment of prompt and delayed fission processes. In the case of this thesis, it will be applied to the analysis of delayed gamma spectra from the FIPPS experiment at ILL.
Search for a new mode of radioactivity: double alpha decay
Christophe THEISEN
CEA - DRF/IRFU/DPhN/LENA
Personal web page : https://irfu.cea.fr/Pisp/christophe.theisen/
Laboratory link : https://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=2647
We propose a theoretical and experimental study of a new type of nuclear radioactivity that remains to be discovered: the double alpha decay. The theoretical part will allow to determine the nucleus for which the experimental signature of the double alpha radioactivity is the most clear. As regards the experimental part of the thesis, it will consist in optimizing the detection device in view of new experiments which could be carried out at CERN and lead to the discovery of this new radioactivity.
Shape coexistence in nuclei around 96Zr
Magdalena Zielinska
This PhD project is focused on nuclear structure, and, more precisely, nuclear shapes in the transitional (A~100) region of the nuclear chart.
The shape is one of the fundamental properties of a nucleus. It is governed by an interplay of macroscopic and microscopic effects like the shell structure. Some of these nuclei are known to exhibit the shape-coexistence phenomenon: the nucleus changes drastically its shape at low excitation energy. Recently, observation of a low-lying deformed state in the magic 96Zr nucleus has been explained by a reorganization of nuclear shells in function of their occupation by protons and neutrons. The present project deals with the neighbouring 100Ru nucleus, which is suggested to present similar features as 96Zr, but is more accessible experimentally. Two experimental techniques will be applied: gamma-ray spectroscopy following neutron capture, and Coulomb excitation, which is the most direct way to determine shapes of nuclear excited states.The PhD student will analyse the data from experiments performed at two facilities: FIPPS (ILL, Grenoble) and HIL (Warsaw University, Poland).
Likelihood-free cosmological parameter inference using theoretical high-order statistics predictions
Research field : Numerical simulation
Jean-Luc STARCK
CEA - DSM/IRFU/SAp/LCS
Personal web page : http://jstarck.cosmostat.org
Laboratory link : http://www.cosmostat.org
The Euclid satellite, to be launched in 2023, will observe the sky in the optical and infrared, and will be able to map large scale structures and weak lensing distortions out to high redshifts. Weak gravitational lensing is thought to be one of the most promising tools of cosmology to constrain models. Weak lensing probes the evolution of dark-matter structures and can help distinguish between dark energy and models of modified gravity. Cosmological parameters are traditionally estimated using a Gaussian likelihood based on theoretical predictions of second order statistic such as the power spectrum or the two point correlation functions. This requires to build a covariance matrices, and therefore need a lot of very heavy n-body simulations. This approach presents also several additional drawbacks: First, second order statistics captures all available information in the data only in the case of Gaussian Random Fields, while matter distribution is highly non-Gaussian showing many features such filaments, walls or clusters. Second, the covariance matrix is cosmology dependent and the noise it generally not Gaussian, both aspects being generally poorly taken into account. Finally, all systematic effects such as masks, intrinsic alignement, baryonic feedback are very difficult to take into account. For all these reasons, a new approach has recently emerged, called likelihood-free cosmological parameter inference which are based on a forward modelling. It has the great advantage to not need covariance matrices anymore, avoiding the storage of huge simulated data set (we typically need 10000 n-body realisations for each set of cosmological parameters). Furthermore, it opens us the door to use high order statistical information and it is relatively straightforward to include all systematics effect. It has however two serious drawbacks, the firsts one is the need of huge GPU ressources to process surveys such as Euclid and the second is that the solution relies on the accuracy of simulations, which could lead to infinite discussion in case the results are different from what is expected. Thanks to a recent breakthrough (Codis, 2021), we have now theoretical tools to predict, for a given set of cosmological parameters, the multi-scale density probability function (pdf) of convergence maps such as the one that will be observed with Euclid.
The goal of this PhD work is to develop an hybrid approach, consisting in a likelihood-free cosmological parameter inference which would be based on the high order statics theoretical prediction rather than n-body simulations. It would therefore have the advantage of both previously described approaches, as it will not need to store huge data set to compute a covariance matrix and it will not require huge CPU/GPU ressources as the forward modelling method. This intense frugality will make this approach highly competitive to constraint the cosmological model using high order statistics in future surveys.
To achieve this goal, the first step will be to build a map emulator, similar to what has been done for 2 point statistics (i.e. the flask method), but which respects accurately the high order predictions. Using this emulator, it will then be possible to use it as a bypass in a recently developed Likelihood Free Inference code. This will allow the use of high order statics such as the l1-norm of the wavelet transform of the convergence to constrain the cosmological parameters, which is an extremely powerful summary statistic (Ajani et al, 2021). The developed method will be used first on the CFIS survey and then on Euclid.
Barthelemy A., Codis S. and Bernardeau F., "Probability distribution function of the aperture mass field with large deviation theory", 2021, MNRAS, 503, 5204;
V. Ajani, J.-L. Starck and V. Pettorino, "Starlet l1-norm for weak lensing cosmology", Astronomy and Astrophysics, 645, L11, 2021.
PROCESSING/ANALYSIS OF NUCLEUS AND CRAB EXPERIMENTAL DATA FOR THE MEASUREMENT OF COHERENT SCATTERING OF REACTOR NEUTRINOS
Research field : Particle physics
Groupe Sources et Réacteurs (GNSR)
Thierry Lasserre
Edoardo MAZZUCATO
CEA - Liste des pôles/Liste des départements/Liste des services/Double Chooz
Personal web page : http://irfu.cea.fr/Pisp/thierry.lasserre/
Laboratory link : https://irfu.cea.fr/en/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=2260
The NUCLEUS experiment aims for the detection of coherent elastic neutrino-nucleus scattering (CEvNS) at the Chooz nuclear power station using ultra-low threshold gram-scale cryogenic detectors. This technology will enable the miniaturization of neutrino detectors and has the potential to probe physics beyond the Standard Model of particle physics in a second kilogram-scale phase. The complete understanding of the NUCLEUS data will be accomplished by a dedicated calibration experiment, called CRAB, which will take place next to the Triga research reactor in Vienna.
The Ph.D. concerns the analysis of data from the first phase of the NUCLEUS experiment by integrating the results of the calibration of the CRAB experiment into the NUCLEUS analysis. The analysis will be carried out according to the following experimental phases: analysis of the commissioning data (TUM, 2022), analysis of the NUCLEUS blank assembly data (TUM, 2023), analysis of the NUCLEUS neutrino data (Chooz, 2024-25) and CRAB data (Munich and Vienna, 2023-25). The work first involves the development of a dedicated analysis chain, based on existing CRESST software packages, to eventually integrate the analysis of NUCLEUS and CRAB data into a common framework. The first step in the analysis typically entails large-scale processing of the raw data on computer clusters, including triggering and energy reconstruction. After this phase, the reconstructed data need to be processed to isolate the expected signals from the various backgrounds. In parallel, calibration data (from radioactive sources, light-emitting diode systems, and CRAB results) and their uncertainties need to be incorporated. Altogether, novel analysis methods have to be developed to exploit the NUCLEUS 4pi-vetoing strategy to suppress backgrounds. Connections to state-of-the-art machine learning techniques to improve analysis performance will be also explored and eventually implemented.
Thin fast photo-detector for time-of-flight and high resolution PET imaging with SiPM
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&voir=3944
In this thesis, we propose to contribute to an ambitious and patented detector based on Cherenkov/Scintillant crystals. The first prototype is currently being tested in the laboratory.
The instrument uses advanced technologies for fast particle detection: a dense scintillator crystal, a microchannel plate photomultiplier for the first side of the crystal, gigahertz amplifiers and fast acquisition modules (WaveCatcher, SAMPIC).
The PhD student will work on the choice of technologies and on the realization of a thin photodetector, with a high temporal resolution (a few tens of ps) intended to instrument the second side of the crystal. The preferred technology today would be a fast SiPM array.
You will test the available SiPM technologies, participate in the design of the photodetector assembly. You will run measurements on test benches and prototypes, and analyze the measured data in order to optimize the temporal, spatial resolution and efficiency of the detector. This will involve a wide range of instrumentation skills: photo-detection, fast electronics (analog and digital, to picosecond accuracy), detector simulations using GEANT4 and GATE software.
The successful candidate will work in the IRFU Department of Particle Physics in close collaboration with the Department of Detectors, Electronics and Computing for Physics. The CaLIPSO group includes two physicists and two students and two post-docs. We collaborate closely with the CNRS-IJC-labs on fast readout electronics, with the CPPM of Marseille and the CEA-SHFJ, on medical imaging devices, with the CEA-DES on image reconstruction algorithms, and with the University of Munster (Germany).
Knowledge of general physics, physics of particle-matter interaction, radioactivity and particle detector principles, as well as a vocation for instrumental work and data analysis are mandatory. Programming skills, Gate/Geant4 simulation and C++ training will be an asset.
Acquired Skills
You will acquire skills in particle detector instrumentation, radiation detector simulation, photo-detection, implementation and operation of fast scanning electronics and data analysis.
Towards the discovery of Charge-Parity violation in the neutrino oscillations
Groupe Neutrinos Accélérateurs (GNA)
Georges VASSEUR
Sara Bolognesi
CEA - DSM/IRFU/SPP
CEA - DRF/IRFU/SPP/TK2
The study of neutrino oscillations entered the precision era with present experiments based on accelerator beams, like T2K. In these experiments, neutrino oscillations are measured by comparing the neutrino rate and spectra at near detectors, placed nearby the accelerator source, and at far detectors, placed hundreds of kilometers away. T2K published in 2020 on the Nature cover first exciting hints of Charge-Parity violation in the lepton sector.
The work proposed for this thesis consists in the analysis of the new data which will be collected by T2K with an upgraded near detector requiring to put in place a new analysis strategy. In particular, for the first time, the measurement of protons and neutrons produced by neutrino interactions will be exploited. New models of neutrino-nucleus interactions will be needed to cope with such additional information: the group proposing this thesis has a deep expertise on the field.
Another item to be addressed in the thesis is the extrapolation of the obtained results to long-term high-statistics measurements and multi-experiment combinations. The study of the most relevant systematic uncertainties will have a direct impact on the design of the next-generation experiments, to which the group is also participating.
The student is expected to participate to the installation and commissioning of new Time Projection Chambers in the Japanese site of the JPARC laboratory end of 2022 and early 2023. This will be a great opportunity for highly-formative hardware experience.
In summary, this thesis will allow to acquire expertise on neutrino oscillations, a highly promising topic for the future of HEP, to develop cutting-edge analysis techniques, to participate to the installation of an innovative detector and to interact with a wide community of nuclear physicists and phenomenologists. The results of the proposed analysis of T2K data will provide worldwide best measurements on neutrino oscillation parameters, notably on the possible first source of Charge-Parity violation in the lepton sector.
Charged particle tracking in heavy-ion collisions in LHCb and data analysis in fixed-target collisions at the LHC
Michael Winn
Alberto Baldisseri
CEA - DRF/IRFU/DPhN/ALICE
CEA - DRF/IRFU/SPhN/ALICE
Created in heavy-ion collisions at the LHC (CERN), the quark gluon plasma (QGP) is an extreme state of matter in which the constituents of nucleons are 'deconfined' sufficiently long in order to be studied.
Among the CERN LHC collaborations, LHCb studies the QGP both in collider mode, but also thanks to a fixed-target programme unique at the LHC.
The current performance of the tracking detectors is limited in the most violent collisions, but several upgrades are foreseen at the horizon of 2030.
The first goal of this thesis is the tracking development in order to assure optimal performances in future heavy-ion data takings. These studies will allow to define the performance parameters necessary to be achieved for the different subdetectors. Furthermore, alternative algorithms based on artificial intelligence will be explored in order to achieve the maximal detector performance. In parallel, an analysis component is proposed based on the fixed-target data. In particular, we propose to measure charm particle production. Unique in this kinematics and its energy range, these fixed-target collision measurements with the LHCb detector at the LHC will allow to establish better the role of charm quarks as observables sensitive of deconfinement.
DETECTION OF 100 eV NUCLEAR RECOILS: CHARACTERISATION OF BOLOMETERS RESPONSE AND APPLICATION TO COHERENT SCATTERING OF REACTOR NEUTRINOS WITH THE NUCLEUS EXPERIMENT.
David LHUILLIER
Modern cryogenic detector technology makes it possible to reach extremely low detection thresholds, of the order of 10 eV, while maintaining a significant active mass, from 1 to 100 g. This gain in sensitivity opens up great prospects for studies in fundamental physics. Indeed, the search for low-mass dark matter particles involves the detection of nuclear recoils in the same 100 eV range. This energy range is also that of the recoils induced by the coherent scattering of reactor neutrinos on nuclei. Accessing this process allows to test the Standard Model through a new neutrino-matter coupling. This thesis proposes the implementation of an innovative method to study precisely the response of bolometers in this unexplored 100 eV range. This is the objective of the CRAB (Calibrated Recoils for Accurate Bolometry) project [1]. It is being developed in collaboration with the NUCLEUS experiment [2], which aims to measure the coherent scattering of reactor neutrinos using CaWO4 bolometers. The first application of the CRAB method will be performed with these detectors.
No absolute calibration method for bolometers currently exists for this new region of interest around 100 eV. Extrapolation of the available measurements to the keV scale is problematic, due to the rapid and non-trivial evolution of the distribution of the different excitation modes of the detection medium: phonons, ionisation and scintillation. Moreover, at such low energies, the details of the crystal structure and the dynamics of defect creation become non-negligible. The CRAB method is based on the radiative capture of thermal neutrons in the cryogenic detector. It gives access for the first time to specific and known nuclear recoils, in the 100 eV range, and uniformly distributed in the volume of the bolometer. Several R&D and validation steps will be carried out in collaboration with the IJCLab in Orsay and the University of Munich (TUM). The final measurement on a NUCLEUS bolometer will use the neutron beam of the TRIGA reactor in Vienna, in collaboration with the TU-Wien University. Applicable to other types of bolometers, this method has potentially a strong scientific impact in the communities of coherent neutrino scattering, light dark matter searches and solid state physics.
A direct contribution of the thesis work to the NUCLEUS experiment will therefore be the absolute calibration of the energy response of CaWO4 detectors via the CRAB measurement. This study will be an entry point for the analyses of the NUCLEUS data. Priority will be given to the exploitation of the muon veto, the development of which has been taken in charge by the DPhN. This active shielding surrounds the entire experimental setup as hermetically as possible with plastic scintillator panels from which light is extracted by optical fibres connected to Silicon Photomultipliers (SiPM). The aim is to sign the passage of cosmic rays in the vicinity of the bolometers, which is the source of the dominant background noise. The candidate will be responsible for the implementation of tools for the analysis of muon veto data and their integration into the analysis chain of the experiment. This work will first validate the intrinsic performances of this detector and then it will be extended to the study of the background noise, a key element of the NUCLEUS measurement. The aim will be to quantify the rejection power of the muon veto and determine the nature of the residual background.
A blank assembly of the experiment is planned for 2022 in Munich to validate the whole apparatus and the background level. Neutrino data collection should start in 2023 at the EDF site, in a room located about 80 metres from the two cores of the Chooz nuclear power plant in the Ardennes. In the end, the thesis work will be divided equally between CRAB and NUCLEUS projects.
T2K Near Detector performance and CP violation measurement in the neutrino's oscillations
Jean-Francois Laporte
Samira Hassani
CEA - DRF/IRFU/SPP/Atlas
CEA - DRF/IRFU/DPHP/TK2
The neutrino masses and flavor mixing are a direct evidence of new physics Beyond the Standard Model (BSM): the study of neutrino oscillations is thus a royal road to the search of new, unexpected phenomena. In particular, the analysis of neutrino and antineutrino oscillations at T2K and NOVA are providing first exciting hints of CP violation in the leptonic sector. This would be a major discovery related with one of the most fundamental questions in High Energy Physics: why there is an asymmetry between matter and antimatter in the Universe?
T2K is a neutrino experiment designed to investigate how neutrinos change from one flavour to another as they travel (neutrino oscillations). An intense beam of muon neutrinos is generated at the J-PARC nuclear physics site on the East coast of Japan and directed across the country to the Super-Kamiokande neutrino detector in the mountains of western Japan. The beam is measured once before it leaves the J-PARC site, using the near detector ND280, and again at Super-Kamiokande: the change in the measured intensity and composition of the beam is used to provide information on the properties of neutrinos.
The work of the proposed thesis will concentrate on the installation, commissioning and scientific exploitation of the High-Angle Time Projection Chamber (High-Angle TPC). The goal of this new detector is to improve the Near Detector performance, to measure the neutrino interaction rate and to constrain the neutrino interaction cross-sections so that the uncertainty in the number of predicted events at Super-Kamiokande is reduced to about 4% (from about 8% as of today). This will allow improving the physics reach of the T2K-II project. This goal is achieved by modifying the upstream part of the detector, adding a new highly granular scintillator detector (Super-FGD), two new TPCs and six Time Of Flight planes.
The new TPCs will be read out by resistive Micromegas detectors and instrumented with a compact and light field cage. The TPC will measure charge; momentum and directions of tracks produced by charged particles and will provide particle identification through dE/dx measurement with excellent efficiency and precision. Detector prototypes of the new TPCs have been successfully tested in Summer 2018, 2019 and 2021 at CERN and DESY test beams validating the detector technologies and their performance.
The IRFU group is heavily involved in the TPC project, especially in Micromegas detectors production and tests. The detector construction is on going for an installation in Japan in 2022.
The first part of the thesis will be devoted to TPC data analyses. The student will contribute to the commissioning and first beam data taking and analyses foreseen in 2023. The work will focus on the characterization of the resistive Micromegas detector. This is an innovative detector, which will exploit for the first time the resistive technology to improve the resolution on track reconstruction in the TPC. The IRFU group has been initiator of both the original Micromegas technology and of its resistive implementation.
A cutting-edge R&D conducted at IRFU has brought today to the deployment of such technology in a real detector. A seminal, unprecedented work of quantitative understanding and simulation of the charge spread in the resistive detector is on going.
New and sophisticated reconstruction algorithm must be developed to fully profit of the new detector capabilities. In particular, the timing information related with the resistive phenomena and encoded in the signal waveforms should be exploited. Indeed the resistive technology brings improved performances but also new challenges: the charge spread over multiple pads, induced by the resistive phenomena, will highly increase the multiplicity of signals to be analyzed.
Machine Learning (ML) methods will be explored to perform background-rejection and particle ID purposes at the pre-selection stage as well as evaluate them for the pattern recognition stage of track reconstruction. ML are known to have improved performance of many experiments in neutrino Physics (SNO, NEXT, NOvA, KamLAND-Zen, EXO-200, MINERvA). Producing images like structures from detectors data allows to benefit of the pattern recognition capabilities of these tools and enhancing useful features of the data, they can improve not only events but also particles classification tasks.
We propose as a first step to apply ML techniques to treat TPC information. The arrival time on the resistive anode plane gives the z coordinate perpendicular to that (x,y) plane. An event in the TPC is represented by two images projecting on (x,y) and (y,z) planes with the color scale being the pad charge to incorporate dE/dx information. This will allow treating the TPC information as images and to use the powerful ML algorithms used in image analysis. We plan to use implementations relying on Convolutional Neural Network (CNN) (for some, adapting the GoogLeNet CNN architecture) originally designed to image recognition. To significantly reduce training time, Graphical Processing Units (GPUs) will be used, which enable to perform computing operations in parallel. At the TPC level, we aim to use such techniques for Particle identification (PID) and possibly for pattern recognition.
Next we plan to use ML techniques combining TPC and the central SFGD for particle identification (muon from pion and from proton) as well as for event classification task. In the ND280, the beam of muon neutrinos interacts predominantly via the Charged Current Quasi Elastic interaction. For the purposes of the oscillation analysis, data are separated by event topology into one of three categories based on number of final state pions (no pions, one charged pion or any number of pions). A repository will be prepared, which will contain the images in a format suitable for the training of different ML algorithms. The samples defined above can be selected by using available data, collected by T2K. Other charged current event will fall in background sample.
A framework will be developed to allow the testing of various algorithms for object detection and classification.
The second part of the thesis will be dedicated to the analysis of the first T2K neutrino beam data, collected with the ND280 Upgrade detector, in order to extract a new, most precise, measurement of neutrino oscillations. Thanks to the increased statistics and the improved control of systematic uncertainties with ND280 upgrade, the project has the potential to achieve the best worldwide constrains on CP violation in the leptonic sector. The work will focus on the definition of the selection of the new ND280 samples, the evaluation of the corresponding experimental systematic uncertainties and the modification of the analysis framework for the fit to the neutrino oscillation parameters. The extraction of near detector constraints must be deeply modified to include the information of outgoing detected protons and neutrons coming from neutrino interactions and nuclei, which are completely missing in the present analysis. In parallel, the theoretical systematic uncertainties will need to be reevaluated on the basis of the new exclusive models of neutrino-nucleus interactions.
LHC luminosity measurement with the ATLAS Liquid Argon Calorimeter and search for long lived massive particles
Groupe Atlas (ATLAS)
Philippe Schwemling
Since the discovery of the Higgs boson efforts are focused on the search for new phenomena, beyond the Standard Model.
One of the important aspects of the comparison between experimental measurements and theory is the need to normalize as
precisely as possible experimental results to theory. This means in practice being able to measure as precisely as
possible the luminosity of the LHC. The goal is to reach a precision better than 1% within the next few years,
a factor two or three better than the precision that has been reached up to now.
After the LHC restart, foreseen in 2022, it is planned to increase the luminosity by a factor of about two. To make
the best out of this luminosity increase, the calorimeter trigger system is being significantly modified and upgraded.
The upgraded trigger system is based on real time analysis of the digitized detector signals.
An essential feature of the upgraded trigger system is its ability to measure the energy deposited in the calorimeter
bunch crossing by bunch crossing. Combined with the stability, excellent linearity and response uniformity of the ATLAS
Liquid Argon calorimeter, the upgraded trigger system offers the potential to measure the luminosity with excellent
linearity and stability performances. A very promising analysis technique would be to use a neural net to process the data.
An other feature of the upgraded trigger system is its ability to keep track of all the interactions taken place in the
detector over a much longer period of time than the main readout. The main readout system is able to keep in memory only
up to four or five consecutive interactions. The trigger system has the capability to keep track of each individual bunch
crossing over a period of time corresponding to several tens of consecutive bunch crossings.
This long term memory feature gives the possibility to compensate real time the effect of charge space accumulation,
which will be crucial for data taken after 2025, at very high luminosity. More importantly, this also opens up the
possibility to detect particles reaching the detector long (several tens or even hundreds of ns, to be compared to the
25 ns between two consecutive bunch crossings) after their production. Such particles are slow and very heavy, and can be
detected almost up to the kinematic limit of 7 TeV. This is significantly higher than the limits reachable by more
classic techniques. Such particles typically appear in many classes of supersymmetric models.
Axion searches with the International Axion Observatory with ultra low background Micromegas detectors
DÉtecteurs: PHYsique et Simulation
Thomas PAPAEVANGELOU
Esther FERRER RIBAS
CEA - DRF/IRFU/DEDIP/DEPHYS
Personal web page : http://irfu.cea.fr/Pisp/esther.ferrer-ribas/
Laboratory link : http://irfu.cea.fr/dedip/index.php
More : https://iaxo.web.cern.ch/content/home-international-axion-observatory
Axions were introduced as the most promising solution in explaining the absence of Charge-Parity symmetry violation in the strong interaction. These neutral, very light particles, interact so weakly with ordinary matter that they could contribute to the Dark Matter. Axion search techniques rely on their interaction with photons. Helioscopes search for axions produced in the solar core by the conversion of plasma photons into axions giving rise to a solar axion flux at the Earth surface, with energy spectrum at the region 1-10 keV.
The International Axion Observatory (IAXO) will achieve a signal-to-background ratio of about 4-5 orders of magnitude better than most sensitive experiments today. BabyIAXO, an intermediate experimental stage of IAXO, will be hosted at DESY (Germany). BabyIAXO is conceived to test all IAXO subsystems (magnet, optics and detectors) at a relevant scale for the final system and thus serve as prototype for IAXO, but at the same time as a fully-fledged helioscope with relevant physics reach in itself, and with potential for discovery. IAXO and BabyIAXO will be equipped with X-ray optics coupled to low background X-ray detectors. The required levels of background are extremely challenging, a factor 10 better than current levels.
The PhD will work on the X-ray detector development in particular of the new generation of Micromegas detectors. The development will be focused on the optimization of the background level by a multi-approach strategy coming from ground measurements, screening campaigns of components of the detector, underground measurements, background models, in-situ background measurements as well as refinement of rejection algorithms. Physics analysis of BabyIAXO data is expected in the last year of the PhD.
Towards a high spatial resolution pixel detector for particle identification: new detectors contribution to physics
Nicolas FOURCHES
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.
BINGO: Bi-Isotope 0nBB Next Generation Observatory
Claudia Nones
CEA - DRF/IRFU/DPHP/GNSR
More : https://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast.php?t=fait_marquant&id_ast=4713
BINGO is a new project funded with an ERC grant. It will set the grounds for a large-scale bolometric experiment searching for neutrinoless double beta decay with a background index of about 10-5 counts/(keV kg y) and with very high energy resolution in the region of interest. These features will enable a search for lepton number violation with unprecedented sensitivity. BINGO is based on luminescent bolometers for the rejection of the dominant alpha surface background. It will focus on two extremely promising isotopes – 100Mo and 130Te – that have complementary merits and deserve to be both considered for future large-scale searches.
The project will bring three original ingredients to the well-established technology of hybrid heat-light bolometers: i) the light-detector sensitivity will be increased by an order of magnitude thanks to Neganov-Luke amplification; (ii) a revolutionary detector assembly will reduce the total surface radioactivity contribution by at least one order of magnitude; (iii) for the first time in an array of macrobolometers, an internal active shield, based on ultrapure ZnWO4 scintillators with bolometric light readout, will suppress the external gamma background.
In this PhD thesis, the student will contribute to the assembly and installation of the MINI-BINGO demonstrator in a new cryostat at the Underground Laboratory of Modane. He/she will participate to the data taking and data analysis. He/she will estimate the final background rejection made possible by the performance of the final detector configuration.
Gluon tomography with exclusive vector meson production
Laboratoire structure du nucléon (LSN) (LSN)
Francesco BOSSU
Franck SABATIE
CEA - DRF/IRFU/SPhN
Laboratory link : http://irfu.cea.fr/Phocea/Vie_des_labos/Ast/ast_service.php?id_unit=7
Thesis: Gluon tomography with exclusive vector meson production
The understanding of the origin of the mass, the spin and the structure of the nucleons (i.e. protons and neutrons) from their elementary constituents (quarks and gluons, collectively called partons) is among the unanswered questions in particle physics. The theoretical framework of the Generalized Parton Distributions (GPDs) encodes the 3-dimensional structure of a nucleon and its study will provide insights on the origin of the fundamental properties of protons and neutrons.
Experimentally, the cleanest method to study the internal structure of nucleons is to collide them with electrons at high energies. CEA/Irfu staff members are among the principal investigators of ongoing experiments at the Jefferson Lab (JLab) in USA, where a high current electron beam up to 11 GeV in energy collides with fixed targets of several types, and of the future experiments at the Electron Ion Collider (EIC), where electrons and protons will collide at energies in the center of mass up to 140 GeV. The high luminosities available at the JLab and at the future EIC allow the study of the properties of the nucleons with high statistical accuracy also via rare processes.
Contrary to the naive expectations, it has been shown that not the valence quarks, but rather the gluons carry the major contribution to the mass and the spin of the nucleons. Therefore, it is crucial to precisely characterize gluons distributions in order to fully understand the properties of the nucleons. In particular, the current knowledge of the GPDs of gluons is rather limited. GPDs are accessible through the study of exclusive processes where all the final state particles are detected, and specifically, gluon GPDs can be accessed via the study of the exclusive electo-production of vector mesons such as the rho, phi et omega mesons.
The goal of this thesis will be to analyze the data taken with the CLAS12 experiment at the Jefferson Lab focusing on measurements of exclusive meson production. Given the large size of the datasets, the student will have the opportunity to develop and apply machine learning algorithms to improve the reconstruction and the selection of event candidates. Extensive studies on simulated data will be necessary to fully understand the data, to train and optimize the candidate selection algorithms, to adapt ML models the real data and to tame possible systematic uncertainties. From the experience gained through the analysis of CLAS12 data, the candidate will also participate in the simulation studies for feasibility and optimization of the future detectors for the EIC for exclusive vector meson electro-production at high energies.
The thesis will be carried out within the Laboratory of Nucleon Structure of the Department of Nuclear Physics of CEA/Irfu. The laboratory is composed by both experimentalists and theorists: the frequent interactions make the work environment very enriching.
Knowledge of particle physics and computer science would help the candidate to quickly actively participate to the data analysis effort. Basics knowledge of particle detectors would be also an advantage to efficiently understand the experimental setup used for data collection.
The student will also have the opportunity to collaborate with several researchers both locally (like IJCLab in Orsay and CPHT at Ecole Polytechnique) and internationally. The student will be part of the CLAS collaboration and will also join the EIC user group that will also require trips to United States for data taking and workshops. The student will have the opportunity to present the result of these research topics to international conferences.
Contact: Francesco Bossù, CEA Saclay – IRFU/DPhN/LSN, (francesco.bossu@cea.fr)
improved secondary electron yield by atomic layer deposition
Research field : Radiation-matter interactions
Laboratoire d'Ingénierie de Systèmes Accélérateurs et Hyperfréquences (LISAH)
Juliette PLOUIN
Mohamed Belhaj
CEA - DSM/IRFU/SACM/LISAH
ONERA - DESP
Multipactor is a parasitic phenomenon that occurs in devices where a microwave is transmitted under vacuum such as electronic vacuum tubes for electron microscopy, resonant cavities and couplers for particle accelerators and microwave circuits. on board the satellites. It consists of an avalanche of electrons set in motion by a radiofrequency field which can cause, under certain conditions, a disturbance of measurements, damage or even destruction of RF devices.
This phenomenon is directly linked to the emission of so-called secondary electrons from a material when it is irradiated with electrons. The secondary electron production yield (SEY for Secondary Emission Yield) is therefore a crucial parameter if we want to greatly reduce the multipactor phenomenon.
This thesis project aims at the fundamental study of SEY of thin films synthesized by Atomic Layer Deposition (ALD). ALD is a thin film synthesis technique used in the microelectronics, photovoltaic, battery industries…, which allows unparalleled control of thickness and chemical composition down to the atomic level on complex surfaces. This deposition technique is therefore a remarkable tool for 1 / studying separately and in a controlled manner the impact of different alloys (chemical composition), and their thickness on the SEY and 2 / directly applying these optimized structures on "real »RF devices. This thesis will be done in collaboration between CEA and ONERA. It combines at the same time a proven deposition technique, means of spectroscopic surface characterizations of peaks and numerical simulations.
Study of coherence losses mechanisms in superconducting resonators by tunneling and X-ray spectroscopy
Research field : Solid state physics, surfaces and interfaces
Laboratoire d'Intégration et Développement des Cavités et Cryomodules (LIDC2)
thomas proslier
Superconducting resonators are used in a wide variety of application; from Qubits or single photon detectors to radio frequency cavities used in particle accelerators. Superconducting quantum bits (Qubits) have attracted increasing attention and significant public investment in recent years. One of the main challenges is to maintain coherence / quantum information long enough to be able to perform calculations. Nowadays, Qubits can achieve a coherence time of about 100 µs and superconducting cavities ~ 100 ms; current research aims at increasing these times by at least an order of magnitude. Although these two superconducting devices (Qubits and cavities) are very different (operating temperature, geometries, etc.), recent experiments indicate that similar microscopic mechanisms limit their performance; Impurities (two-level systems, magnetic impurities, etc.) present within the dielectrics or at the interface between the dielectric and the superconducting film have been identified as potential candidates for loss of coherence. In addition, the superconducting properties of films, and in particular their spatial variations, are also important parameters that limit the resonators performances, and must therefore be systematically characterized.
This thesis project, in collaboration with IIT in the USA, CEA/SPEC and CERN, aims at studying by tunneling (ST) and X-ray photoemission (XPS) spectroscopies these superconducting surface parameters as well as the characteristic spectral signatures of impurities on new materials used for superconducting cavities and bits. Quantum. The aim is to provide a detailed understanding of these phenomena, to establish correlations between the measurements taken on samples and the performance of superconducting devices and finally to be able to propose technological solutions to improve their performance.
Study of fluctuations and of the emergence of spatial structures associated to branching transport process. Application to neutronic transport theory and quantum mechanics.
Research field : Theoretical Physics
Eric DUMONTEIL
Personal web page : http://eric.dumonteil.free.fr
Laboratory link : https://irfu.cea.fr/
More : https://irfu.cea.fr/dphn/index.php
The study of branching random walks allows to characterize many phenomena such as the propagation of epidemics, genetic transmission within populations, the fundamental mode of quantum systems or the transport of neutrons in fissile media, just to name a few.
In this last field, for example, recent work has shown that spatial structures (clustering) can emerge within the neutron population present in a nuclear reactor, which can be described using the spatial correlation function. Approaches based on the use of quantum field theory (QFT) have allowed to compute this correlation function, but show limitations with respect to the study of some quantities (in particular concerning the computation of various observables in the vicinity of the critical point, where productions and disappearances exactly compensate).
This PhD thesis therefore proposes to develop a Lagrangian approach for this purpose, by copying a technique developed by Doi and Peliti and taken up by Garcia-Millan, in order to recover the results of the QFT approach and then to extend them to various observables. In this aim, the spatial transport of the considered species (neutrons in reactor physics, viruses in epidemiology, configurations in quantum mechanics) will be taken into account. The results of these formal developments can then be confirmed numerically using a simplified Monte-Carlo code already developed in Python. It will therefore be necessary to implement in this code the calculation of different quantities of interest (temporal and spatial correlations, size and fluctuations of the population, ...), and to carry out a spectral analysis of the obtained distribution (calculation of the eigenmodes of the system), to finally try to extrapolate the results obtained for critical or over/sub-critical environments. A last part of the PhD work will consist in investigating the consequences of this approach in the field of neutronics (calculation of the fluctuations of the neutron population in the vicinity of the critical point, and characterization of the clustering effect) as well as in the field of quantum mechanics (study of the eigenmodes of a quantum system by a Nagasawa type approach, i.e. by being interested in the equivalence between the equations of the diffusion in real time and in complex time).
Numerical and experimental study of a small cryogenic pulsating heat pipe
Research field : Thermal energy, combustion, flows
Laboratoire Cryogénie et Stations d'Essais (LCSE)
Bertrand BAUDOUY
CEA - DRF/IRFU/DACM/LCSE
Recently the development of passive thermal links with high efficiency attracts attention for the cooling of miniature devices and energy savings purposes. One such device is the Pulsating Heat Pipe (PHP), built from shaped capillary tubes usually closed. Due to the phase change phenomenon of the included working fluid, a PHP can transfer heat fluxes about several dozen Watts at room but also low temperature. Nowadays, the dynamic and thermal operation of PHP is not yet fully understood due to the lack of a real fundamental understanding of the two-phase heat and mass transfer coupling mechanism within the PHP. Hence, the design of such thermal links is based on heuristic methods based on experimental data and simple computations. This project aims at developing experimental and numerical tools to comprehend the capillary two-phase heat and mass transfers for this particular heat pipe and to implement such a small heat pipe in an MRI system. A small dimension heat pipe will be constructed and tested at CEA Paris-Saclay. The PHP heat and mass transfer modeling will be developed with an open-source software based on finite volume method (OpenFoam) at the Wroclaw University of Science and Technology (WUST).
Weak values in quantum mechanics: conceptual questions
Research field : Various
Laboratoire de recherche sur les sciences de la matière
Alexei Grinbaum
CEA - DRF/IRFU/DIR/LARSIM
Personal web page : https://irfu.cea.fr/Pisp/alexei.grinbaum/
Weak values arise from weak measurements, i.e. non-projective methods of obtaining information about quantum states without causing the wavefunction collapse. They lead to a number of paradoxes studied in the literature since the 1980s (cf. Aharonov et al. PRL 60, 1351, 1988), e.g. the Hardy paradox, the Cheshire Cat paradox, counterfactual communication, or retrocausality. Experiments demonstrating the reality of weak values have recently been performed by several groups. While the implications of weak values for quantum technology are widely discussed, they are also important conceptually and philosophically. In this PhD work, the candidate will aim at gaining a better understanding of the key notions involved in these paradoxical findings, viz. "a value of an observable", "quantum system", "localisation of a property", "time of measurement", in order to improve a foundational understanding of quantum physics. Mathematical tools will include postquantum models and generalized probabilistic theories. While this research will be mathematical and conceptual in nature, the candidate will also seek to propose new non-classical communication protocols and experimental setups that may help to confirm our theoretical findings. Publications are expected in physics journals (PRL, PRA, NJP, Quantum) and/or philosophy of physics journals (Found. Phys., SHPMP). Collaborations are expected with groups in Austria, Belgium, UK, and Israel.