12 sujets IRFU/DPhN

Dernière mise à jour : 04-07-2022


• Astrophysics

• Nuclear physics

• Particle physics

• Theoretical Physics

 

Study of the sources of gravitational waves with long duration of emission

SL-DRF-22-0370

Research field : Astrophysics
Location :

Service de Physique Nucléaire (DPhN)

Groupe Théorie Hadronique

Saclay

Contact :

Hervé Moutarde

Starting date : 01-10-2022

Contact :

Hervé Moutarde
CEA - DRF/IRFU/SPhN/Théorie Hadronique

33 1 69 08 73 88

Thesis supervisor :

Hervé Moutarde
CEA - DRF/IRFU/SPhN/Théorie Hadronique

33 1 69 08 73 88

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

Prompt and non-prompt quarkonium production in the Pb-Pb collisions at 5 TeV of the LHC Run 3

SL-DRF-22-0369

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

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

Saclay

Contact :

Javier CASTILLO

Starting date : 01-10-2022

Contact :

Javier CASTILLO
CEA - DRF/IRFU/DPhN/LQGP

+33 169087255

Thesis supervisor :

Javier CASTILLO
CEA - DRF/IRFU/DPhN/LQGP

+33 169087255

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

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

A few micro-seconds after the Big Bang, the Universe was in a quark gluon plasma (QGP) state. Such state is predicted by Quantum Chromodynamics, which is the theory of strong interactions, and should be reached at very high temperature or energy density. Such conditions are reproduced in ultra-relativistic heavy ion collisions at the LHC at CERN.

Among the various QGP observables, the study of hadrons with heavy-flavour quarks (charm c or beauty b) and quarkonia (c-cbar or b-bbar bound states) is particularly important to understand the properties of the QGP.

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

SL-DRF-22-0401

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

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

Saclay

Contact :

Thomas MATERNA

Starting date : 01-10-2022

Contact :

Thomas MATERNA
CEA - DRF/IRFU/DPhN/LEARN

0169084091

Thesis supervisor :

Thomas MATERNA
CEA - DRF/IRFU/DPhN/LEARN

0169084091

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

Laboratory link : http://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_groupe.php?id_groupe=498

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 modelling 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.

These studies will be conducted in collaboration with the LEPH laboratory (CEA DES/IRESNE/DER/SPRC) which is developing fission fragment de-excitation code FIFRELIN.
NEW PATHS FOR THE STUDY OF HEAVY NUCLEI

SL-DRF-22-0247

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

barbara sulignano

Starting date : 01-10-2022

Contact :

barbara sulignano
CEA - DRF/IRFU/DPhN/LENA

01 69 08 42 27

Thesis supervisor :

barbara sulignano
CEA - DRF/IRFU/DPhN/LENA

01 69 08 42 27

Hunting for super heavy elements is one of the most exciting and active topics during the last few years and has already produced new elements such as 113, 115, 117 and 118 in accelerator experiments. All these nuclei can be produced through fusion-evaporation reactions. However their studies are greatly hampered by the extremely low production rates, hence experimental information in this region is very scarce. The high-intensity stable beams of the superconducting linear accelerator of the SPIRAL2 facility at GANIL coupled with the Super Separator Spectrometer (S3) 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 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.

Search for a new mode of radioactivity: double alpha decay

SL-DRF-22-0356

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Christophe THEISEN

Elias KHAN

Starting date : 01-10-2022

Contact :

Christophe THEISEN
CEA - DRF/IRFU/DPhN/LENA

01 69 08 74 54

Thesis supervisor :

Elias KHAN
CNRS - Université Paris-Saclay - IJCLab Orsay

+33 1 69 15 71 73

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.
First measurement of the pygmy resonance using neutron inelastic scattering at GANIL/NFS

SL-DRF-22-0240

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Marine VANDEBROUCK

Diane DORÉ

Starting date : 01-10-2022

Contact :

Marine VANDEBROUCK
CEA - DRF/IRFU


Thesis supervisor :

Diane DORÉ
CEA - DRF/IRFU

01.69.08.41.24

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.

Shape coexistence in nuclei around 96Zr

SL-DRF-22-0277

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Magdalena Zielinska

Starting date : 01-10-2022

Contact :

Magdalena Zielinska
CEA - DRF/IRFU/DPhN/LENA

01 69 08 74 86

Thesis supervisor :

Magdalena Zielinska
CEA - DRF/IRFU/DPhN/LENA

01 69 08 74 86

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).

Charge exchange process and beta force function in the beta decay of fission products

SL-DRF-22-0410

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

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

Saclay

Contact :

Alain LETOURNEAU

Starting date : 01-10-2022

Contact :

Alain LETOURNEAU
CEA - DRF/IRFU/DPhN/LEARN

33 (0)1 69 08 76 01

Thesis supervisor :

Alain LETOURNEAU
CEA - DRF/IRFU/DPhN/LEARN

33 (0)1 69 08 76 01

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.

Charged particle tracking in heavy-ion collisions in LHCb and data analysis in fixed-target collisions at the LHC

SL-DRF-22-0097

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPhN)

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

Saclay

Contact :

Michael Winn

Alberto Baldisseri

Starting date : 01-10-2022

Contact :

Michael Winn
CEA - DRF/IRFU/DPhN/ALICE

+33 1 69 08 55 86

Thesis supervisor :

Alberto Baldisseri
CEA - DRF/IRFU/SPhN/ALICE

+33 169089333

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

Created in heavy-ion collisions at the LHC (CERN), the quark gluon plasma (QGP) is an extreme state of matter in which the constituents of nucleons are 'deconfined' sufficiently long in order to be studied.

Among the CERN LHC collaborations, LHCb studies the QGP both in collider mode, but also thanks to a fixed-target programme unique at the LHC.

The current performance of the tracking detectors is limited in the most violent collisions, but several upgrades are foreseen at the horizon of 2030.

The first goal of this thesis is the tracking development in order to assure optimal performances in future heavy-ion data takings. These studies will allow to define the performance parameters necessary to be achieved for the different subdetectors. Furthermore, alternative algorithms based on artificial intelligence will be explored in order to achieve the maximal detector performance. In parallel, an analysis component is proposed based on the fixed-target data. In particular, we propose to measure charm particle production. Unique in this kinematics and its energy range, these fixed-target collision measurements with the LHCb detector at the LHC will allow to establish better the role of charm quarks as observables sensitive of deconfinement.
DETECTION OF 100 eV NUCLEAR RECOILS: CHARACTERISATION OF BOLOMETERS RESPONSE AND APPLICATION TO COHERENT SCATTERING OF REACTOR NEUTRINOS WITH THE NUCLEUS EXPERIMENT.

SL-DRF-22-0337

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPhN)

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

Saclay

Contact :

David LHUILLIER

Starting date : 01-10-2022

Contact :

David LHUILLIER
CEA - DRF/IRFU/DPHN/LEARN

01 69 08 94 97

Thesis supervisor :

David LHUILLIER
CEA - DRF/IRFU/DPHN/LEARN

01 69 08 94 97

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.

Gluon tomography with exclusive vector meson production

SL-DRF-22-0390

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire structure du nucléon (LSN) (LSN)

Saclay

Contact :

Francesco BOSSU

Franck SABATIE

Starting date : 01-10-2021

Contact :

Francesco BOSSU
CEA - DRF/IRFU/SPhN


Thesis supervisor :

Franck SABATIE
CEA - DRF/IRFU/SPhN

01 69 08 32 06

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)
Study of fluctuations and of the emergence of spatial structures associated to branching transport process. Application to neutronic transport theory and quantum mechanics.

SL-DRF-22-0290

Research field : Theoretical Physics
Location :

Service de Physique Nucléaire (DPhN)

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

Saclay

Contact :

Eric DUMONTEIL

Starting date : 01-10-2022

Contact :

Eric DUMONTEIL
CEA - DRF

+33169085576

Thesis supervisor :

Eric DUMONTEIL
CEA - DRF

+33169085576

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).

 

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