8 sujets IRFU/DPhN

Dernière mise à jour : 28-11-2020


• Nuclear Physics

• Nuclear physics

• Particle physics

• Theoretical Physics

 

Pushing ab initio calculations of atomic nuclei to higher precision

SL-DRF-21-0293

Research field : Nuclear Physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Thomas DUGUET

Vittorio SOMA

Starting date : 01-10-2021

Contact :

Thomas DUGUET
CEA - DRF/IRFU/DPhN/LENA

0169082338

Thesis supervisor :

Vittorio SOMA
CEA - DRF/IRFU/DPhN/LENA

0169083236

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

The theoretical description of atomic nuclei from first principles, or in a so-called ab initio fashion, has become possible only recently thanks to crucial advances in many-body theory and the availability of increasingly powerful high-performance computers. Such ab initio techniques are being successfully applied to study the structure of nuclei starting from the lighter isotopes. Still, extensions to heavy elements and nuclear reactions are posing considerable difficulties. The objective of the thesis is to contribute to this on-going progress in nuclear many-body theory. The project will focus on a developing ab initio technique (the so-called Gorkov-Green function approach, devised at CEA Saclay) designed to describe open-shell or superfluid systems (the majority of atomic nuclei). After the first promising applications to light and medium-mass nuclei, the method faces crucial upgrades to reach the precision and competitiveness of state-of-the-art approaches. The proposed work will aim to put in place the necessary tools towards this direction.

It will exploit the latest advances in nuclear theory, including the use of nuclear interactions from chiral effective field theory and renormalisation group techniques, as well as high-performance computing codes and resources. The work will consist in formal developments, computational tasks and application of the new technology to cases of experimental interest. International collaborations are envisaged.
Continuum QCD approaches and 3D structure of the nucleon

SL-DRF-21-0297

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire structure du nucléon (LSN) (LSN)

Saclay

Contact :

Cédric Mezrag

Hervé Moutarde

Starting date : 01-10-2021

Contact :

Cédric Mezrag
CEA - DRF/IRFU/DPhN/LSN


Thesis supervisor :

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

33 1 69 08 73 88

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

Most of the visible mass of the universe is contained in nucleons. However, the origin of this mass remains mysterious, with the portion from the Higgs mechanism in standard renormalization schemes corresponding to only a few percent of the total mass. The answer is to be found in the dynamics of strong interaction, described by the theory of quantum chromodynamics (QCD) in terms of quarks and gluons. Thus, the interaction between quarks and gluons is responsible for the emergence of known and measured properties of hadrons such as their masses or spins.

There is now a strong theoretical and experimental dynamic to determine the 3D structure of hadrons in terms of quarks and gluons. From a theoretical point of view, the classical tools of quantum field theory, namely perturbative expansion, do not allow the study of the emerging properties of hadrons. The latter are inherently non- disruptive.

The aim of this thesis is to develop and use a non-perturbative formalism based on the Dyson-Schwinger and Bethe-Salpeter equations to determine the 3D structure of hadrons, in particular the nucleon. Different dynamic assumptions will be used to obtain a 3D mapping of the charge, mass and orbital angular momentum effects. A comparison of the results obtained with the experimental data will be carried out in collaboration with the other LSN members.
INVESTIGATION OF THE NUCLEAR TWO-PHOTON DECAY IN SWIFT FULLY STRIPPED HEAVY IONS

SL-DRF-21-0139

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Wolfram KORTEN

Starting date : 01-10-2021

Contact :

Wolfram KORTEN
CEA - DRF/IRFU/DPhN/LENA

+33169084272

Thesis supervisor :

Wolfram KORTEN
CEA - DRF/IRFU/DPhN/LENA

+33169084272

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

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

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

The nuclear two-photon, or double-gamma decay is a rare decay mode in atomic nuclei whereby a nucleus in an excited state emits two gamma rays simultaneously. Even-even nuclei with a first excited 0+ state are favorable cases to search for a double-gamma decay branch, since the emission of a single gamma ray is strictly forbidden for 0+ ? 0+ transitions by angular momentum conservation. The double-gamma decay still remains a very small decay branch (<1E-4) competing with the dominant (first-order) decay modes of atomic internal-conversion electrons (ICE) or internal positron-electron (e+-e-) pair creation (IPC). Therefore we will make use of a new technique to search for the double-gamma decay in bare (fully-stripped) ions, which are available at the GSI facility in Darmstadt, Germany. The basic idea of our experiment is to produce, select and store exotic nuclei in their excited 0+ state in the GSI storage ring (ESR). For neutral atoms the excited 0+ state is a rather short-lived isomeric state with a lifetime of the order of a few tens to hundreds of nanoseconds. At relativistic energies available at GSI, however, all ions are fully stripped of their atomic electrons and decay by ICE emission is hence not possible. If the state of interest is located below the pair creation threshold the IPC process is not possible either. Consequently, bare nuclei are trapped in a long-lived isomeric state, which can only decay by double-gamma emission to the ground state. The decay of the isomers would be identified by so-called time-resolved Schottky Mass Spectroscopy. This method allows to distinguish the isomer and the ground state state by their (very slightly) different revolution time in the ESR, and to observe the disappearance of the isomer peak in the mass spectrum with a characteristic decay time. An experiment to search for the double-gamma decay in 72Ge and 70Se has already been accepted by the GSI Programme Committee and should be realised in 2021/22.
Testing nuclear interaction at the dripline

SL-DRF-21-0181

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Aldric REVEL

Anna CORSI

Starting date : 01-10-2021

Contact :

Aldric REVEL
CEA - DRF/IRFU/DPhN/LENA


Thesis supervisor :

Anna CORSI
CEA - DRF/IRFU/DPhN/LENA

01 69 08 7554

The exploration of nuclei close to the limit of their existence (called dripline) offers the unique opportunity to observe and study many phenomena not - or insufficiently - predicted by theory such as the appearance of neutron "halos" as well as the emergence of new magic numbers and the disappearance of those observed in nuclei close to stability.

The proposed thesis topic revolves around the study of these emerging phenomena in exotic nuclei (see beyond dripline) via the analysis of data from experiments carried out in RIKEN (Japan) and using the state-of-the-art experimental devices SAMURAI and MINOS which are key for the study of these phenomena.

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

SL-DRF-21-0329

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

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

Saclay

Contact :

Javier CASTILLO

Starting date : 01-10-2021

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.
Towards super heavy elements: new paths for the study of heavy nuclei

SL-DRF-21-0371

Research field : Nuclear physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire études du noyau atomique (LENA) (LENA)

Saclay

Contact :

Barbara Sulignano

Starting date : 01-10-2021

Contact :

Barbara Sulignano
CEA - DSM/IRFU/SPhN/LENA

0169 08 42 27

Thesis supervisor :

Barbara Sulignano
CEA - DSM/IRFU/SPhN/LENA

0169 08 42 27

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 whole SIRIUS detector.

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 employing the new alternative method using multi-nucleon transfer reactions.

CALIBRATION OF BOLOMETERS AT THE KeV SCALE AND NEUTRINO COHERENT SCATTERING WITH THE NUCLEUS EXPERIMENT

SL-DRF-21-0270

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 : 01-10-2021

Contact :

David LHUILLIER
CEA - DSM/IRFU/SPhN/MNM

01 69 08 94 97

Thesis supervisor :

David LHUILLIER
CEA - DSM/IRFU/SPhN/MNM

01 69 08 94 97

Laboratory link : http://irfu.cea.fr/dphn/Phocea/Vie_des_labos/Ast/ast_sstheme.php?id_ast=31&voir=technique

The central topic of this thesis is the NUCLEUS experiment, whose motivation is to measure the coherent scattering of neutrinos emitted by the reactors of the EDF power plant at Chooz, in the Ardennes. Although, in the MeV energy range that concerns us, coherent scattering on nuclei is the most probable mode of interaction of neutrinos with matter, it is extremely difficult to detect because its only signature is the tiny recoil of the target nucleus. Thus the first observation of this process dates from 2017 only, with neutrinos of a few 10 MeV from the Oak Ridge spallation source. Measurements at the reactors have yet to be made, and NUCLEUS aims to carry out a precise study of this as yet unexplored neutrino-matter coupling, with a unique sensitivity to potential new physics in the electroweak sector of the standard model. Coherent scattering differs from the beta-inverse reaction used up to now by an interaction cross section several orders of magnitude higher allowing a miniaturization of the detectors: only 10g of target for the first phase of NUCLEUS. Finally, the absence of a reaction threshold (instead of 1.8 MeV for the beta-inverse reaction) could also allow direct monitoring of the accumulation of plutonium in the nuclear reactor cores.

NUCLEUS will use sapphire (Al2O3) and calcium tungstate (CaWO4) bolometers in the form of 5 mm edge cubic crystals. A detection threshold of 20 eV has already been reached with this technology. The thesis work proposed here will focus on two central aspects of the experiment: the calibration of the detectors and the rejection of cosmic rays, the main source of background. An accurate calibration is indeed crucial to study coherent scattering and to reach the best sensitivity on a potential new physics. Although the energy range of the expected nuclear recoils, of the order of 100 eV, is above the achieved detection thresholds, no absolute calibration method for bolometers currently exists for this new region of interest. The extrapolation of the available measurements from the keV scale is problematic due to a rapid and non-trivial evolution of the contribution of the different excitation modes: phonons, ionization and scintillation. A new method proposed by the Department of Nuclear Physics of CEA-Saclay (DPhN) would give access for the first time to calibrated nuclear recoils, in the 100 eV range and uniformly distributed in the volume of the bolometer. The validation of this method and a first measurement with a NUCLEUS bolometer will be developed during the thesis, in collaboration with the IJCLab d'Orsay, the University of Munich (TUM) and the University of Vienna (TU Wien). Applicable to different types of bolometers, this method has potentially a strong scientific impact towards coherent neutrino scattering programs, light dark matter research but also solid state physics.

DPhN is also heavily involved in the development of the NUCLEUS muon veto. This active shielding surrounds as hermetically as possible the central detectors with plastic scintillator panels whose light is extracted by optical fibers connected to Silicon-Photomultipliers (SiPM). Its purpose is to sign the passage of cosmic rays near the bolometers in order to reject any event (potentially background) during the next ~100 microseconds. Data from this detector is a natural input to the NUCLEUS analysis. The start of the data collection on EDF site is planned for the end of 2022 - beginning of 2023.

Finally, the DPhN is also at the origin of the STEREO experiment which is motivated by the search for sterile neutrinos and the precise measurement of the neutrino spectrum resulting from the fission of 235U. It is installed at the ILL research reactor and is completing its data collection this year. Part of the thesis work could be oriented towards combining the final results of STEREO with those of other neutrino experiments, an effort already started with the PROSPECT collaboration. Some of the techniques involved in spectrum unfolding and global fit could be transferable to NUCLEUS.



Organization of the work:

The priority at the beginning of the thesis will be put on the development of the calibration method for 100 eV bolometers with a first step of proof of concept at CEA and Orsay in 2021-22, then a measurement with the a NUCLEUS bolometer in Germany in 2022-23. This work should lead to several publications.

Involvement in the analysis of NUCLEUS data will be stepped up in the second part of the thesis. The entry point will be the exploitation of data from the muon veto, installed on the EDF site from the end of 2022. The first work will be the optimization of gains and thresholds for each SiPM in order to ensure a high rejection of ambient gamma rays, a high muon detection efficiency and a controlled acquisition dead time. An automatic monitoring of the evolution in time of the performances will be set up. Then further analysis will focus on a specific source of background generated by cosmic rays.

In connection with the work on the calibration of bolometers, sensitivity studies could be carried out within the framework of low energy tests of the standard model accessible by NUCLEUS: evolution of sin2_theta_W, magnetic moment of the neutrino ... A synergy with some developments of the final analysis of STEREO would then be exploitable.

Through this work the student will have a complete training as an experimental physicist with aspects of simulation, detector development and data analysis. The physics topics addressed, coherent neutrino scattering and bolometer calibration, are very active in the community and will offer many research perspectives at the end of the thesis. The student will evolve in international collaborations. Within the CEA he (she) will benefit from the "transverse" character of the neutrino and will be in regular interaction with the nuclear physics, particle physics and reactor physics communities.

A simultaneous determination of parton-distribution and fragmentation functions using artificial neural networks

SL-DRF-21-0317

Research field : Theoretical Physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire structure du nucléon (LSN) (LSN)

Saclay

Contact :

Valerio Bertone

Hervé Moutarde

Starting date : 01-10-2021

Contact :

Valerio Bertone
CEA - DRF/IRFU/DPhN/LSN


Thesis supervisor :

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

33 1 69 08 73 88

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

The general goal of this project is a better understanding of the internal structure of hadrons. This problem is addressed in the context of Quantum Chromodynamics (QCD) whose basic building blocks are quarks and gluons. Useful information concerning the hadronic structure is thus encoded in the so-called parton distribution functions (PDFs), that describe how hadrons turn into quarks and gluons, and in the fragmentation functions (FFs), that instead describe how quarks and gluons turn into hadrons. Due to the fact that QCD is strongly coupled at energies of the order of the typical hadronic mass, PDFs and FFs cannot be computed from first principles using perturbation theory. A common solution to this problem consists of paramterising PDFs and FFs and determining them from fits to experimental data. So far, most of the PDF and FF determinations have been obtained separately considering experimental data that are sensitive to only one of them. The subject of this project is a simultaneous determination of PDFs and FFs. The advantage of such a simultaneous determination is a better exploitation of the experimental data that will eventually lead to a better knowledge of PDFs and FFs and thus of the hadronic structure. Given the complexity of the task, PDFs and FFs will be parameterised in terms of artificial neural networks (ANNs). The use of ANNs helps reduce the parametric bias leading to a more accurate determination of PDFs and FFs.

 

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