3 sujets IRFU/DPhN

Dernière mise à jour : 21-01-2021


««

• Particle physics

 

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.

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

SL-DRF-21-0500

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 : 01-10-2021

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.
Gluon tomography with exclusive vector meson production

SL-DRF-21-0568

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/DPhN/LSN


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)

 

Retour en haut