11 sujets IRFU

Dernière mise à jour : 04-06-2020


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• Particle physics

 

Measurement of the Higgs boson properties in the diphoton decay channel, and calibration of the precision timing distribution in the CMS detector

SL-DRF-20-0393

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe CMS (CMS)

Saclay

Contact :

Mehmet Ozgur SAHIN

Fabrice COUDERC

Starting date : 01-10-2020

Contact :

Mehmet Ozgur SAHIN
CEA - DRF/IRFU/DEDIP/STREAM

01 69 08 14 67

Thesis supervisor :

Fabrice COUDERC
CEA - DRF/IRFU/DPHP/CMS

01 69 08 86 83

After the observation of a Higgs boson which is compatible with the predictions of the Standard Model of particle physics at the ATLAS and CMS detectors in 2012, the precise measurements of its properties is now one of the major goals of the high energy physics. The Higgs boson decaying into two photons (H -> GG decay channel) provides a final state with an invariant mass peak that can be reconstructed with high precision. As a consequence, despite the small branching ratio predicted by the SM (approximately 0.2%), H -> GG was one of the two most important channels involved in the discovery of the Higgs boson together with its decay to four leptons. The proposed PhD thesis topic aims at measuring the different Higgs boson couplings using Artificial Intelligence (AI) with a state-of-the-art deep learning model, where a multi-classifier will be designed to make use of all possible ingredients of the H -> GG analyses to provide the most optimal separation with the other non-Higgs SM processes, and hence, will achieve the utmost sensitivity for this particular decay channel in the CMS experiment. Furthermore, the LHC will undergo a High Luminosity (HL) upgrade which will deliver around ten times more integrated luminosity with a downside of imposing harsher conditions for the CMS detector. An accompanying upgrade of the CMS detector (Phase II upgrade) is foreseen to not only cope with these harsher conditions but also significantly improve the performance of the detector. One of the most important aspects of this upgrade is the ability to tag events with very high timing resolution, which will also improve reconstruction of Higgs particles in the H -> GG decay channel. The successful candidate is expected to contribute to the timing upgrade of the CMS detector, particularly to the fast monitoring and calibration of the high-precision clock distribution.

At the start of the project, the successful candidate will have a chance to explore possible improvements in the H -> GG analysis with ~140 fb-1 of data collected with the CMS detector in Run II with an established framework. The candidate will introduce a state-of-the-art machine learning technique for the Run III and foreseen upgrade of the detector. They will perform the H -> GG analysis using this technique with the first Run III data collected in 2021 and 2022 (expected to reach an integrated luminosity of ~115 fb-1). The precision timing distribution calibration and monitoring module will be employed in multiple timing detectors in the CMS experiment. Overall, both aspects of the project will provide a high visibility for the candidate within the collaboration and in the field.
Toward high-precision measurements of neutrino oscillations in the futur long baseline experiments

SL-DRF-20-0424

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPhN)

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

Saclay

Contact :

Alain LETOURNEAU

Starting date : 01-10-2020

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

The neutrino is currently the only particle in the standard model whose description is not entirely contained in it. His study therefore opens the way to the exploration of a new physics and to addressing very fundamental questions such as the preponderance of matter over antimatter in the universe. Future experiments with accelerator neutrinos (DUNE and T2HK) will measure its oscillation properties with unprecedented accuracy, which will require a high degree of control of uncertainties at the percent level.

One of the dominant uncertainties today is the one associated with the modelling of the neutrino interaction inside the detector. A decrease of this uncertainty would immediately imply an increase in the sensitivity of those experiments.

In this thesis work, we propose to improve the description of the neutrino-nuclei interaction, mainly the modelling of the final state of the interaction, and to evaluate its impact on the sensitivity of current and future experiments. The work will be based on the use and development of a nuclear cascade code coupled with measurement results. The results, coupled with an improvement of the near detector, would be used in the ongoing T2K experiment to improve the measurement of neutrino oscillations.

This work will also benefit to define the characteristics of the near detector in the DUNE experiment, whose components will be tested and validated at IRFU.
PRODUCTION OF ANTIHYDROGEN IONS THROUGH CHARGE EXCHANGE REACTION ON POSITRONIUM

SL-DRF-20-0474

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Antimatière et gravitation (GAG)

Saclay

Contact :

Pascal DEBU

Starting date : 01-10-2020

Contact :

Pascal DEBU
CEA - DRF

0169081399

Thesis supervisor :

Pascal DEBU
CEA - DRF

0169081399

Description

This thesis takes place in the GBAR experiment at CERN, which aims to measure the acceleration of gravity on antihydrogen. The specificity of the experiment is to use positive antihydrogen ions to produce ultra-cold antihydrogen atoms, allowing an accurate measurement of their free fall. To produce antihydrogen ions, antiprotons ( p ) must interact on a cloud of positronium (Ps), the bound state of an electron and a positron. Two successive reactions are used:



p + Ps -> H + e- et H + Ps -> H+ + e- .



Only the material counterpart of the first reaction,

p +Ps -> H + e+, was observed with 211 events. Therefore, there are only theoretical estimates of the antihydrogen ion production rate for the experiment. These estimates are subject to significant uncertainties with respect to low-energy three- and four-body interactions.

The first objective of the thesis is to manufacture and use a beam of hydrogen atoms to measure the effective cross-section of the 2nd reaction where incident antihydrogen is replaced by these hydrogen atoms. These measurements will validate the theoretical calculations and optimize the experimental conditions for GBAR (incident energy, Ps excitation level) with high statistics. The second objective is to carry out these measurements with antihydrogen atoms, with much less statistics, but with the aim of producing for the first time H + anti ions.



Group/lab/supervision

The host team includes six physicists, including the spokesperson for the collaboration, and a thesis student. GBAR is an international collaboration involving about 50 physicists from 18 laboratories.

Work proposed

At the start of the thesis, the experiment will be at the end of its installation at CERN. The student will participate in the measurements with the hydrogen beam (October 2020 - mid 2021). This work will cover the understanding of detectors as well as simulation of the experiment, estimation of efficiencies, background noise, calculation of effective cross-sections and comparison with theoretical predictions. Systematic measurements with antiprotons will start from the second half of 2021 when the antiproton beam is operational. The results will be presented at conferences and published.



Training and skills required

The student must have training in experimental corpuscular physics. He will need to acquire programming and instrumentation skills, and will be able to work in a team environment.



Skills acquired

At the end of the thesis, the student will have acquired knowledge in fundamental physics (particle and atomic physics), instrumentation (ultra-high vacuum techniques, trace detectors, lasers, electronics) and programming. He will have worked in a very competitive international environment.



Collaborations/Partnerships

The realization of the experiment is conducted as an international project. Much of the work will be done at CERN.



Contacts

Scientist :

P. Debu (thesis director), L. Liszkay (responsible for the production of positrons and positronium), P. Pérez (spokesman for the experiment).

The NUCLEUS experiment: toward a precision measurement of coherent elastic neutrino-nucleus scattering at reactors

SL-DRF-20-0407

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Sources et Réacteurs (GNSR)

Saclay

Contact :

Matthieu Vivier

Thierry Lasserre

Starting date : 01-10-2020

Contact :

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

0169086626

Thesis supervisor :

Thierry Lasserre
CEA - DRF/IRFU/SPP

0169083649

Since the first detection of the neutrino in 1956 at the Savannah River power plant (USA), nuclear reactors keep playing a central role in the understanding of the fundamental properties of the neutrinos. Neutrinos are electrically neutral elementary particles which can be of three different flavors, each of them being associated to the electron, muon and tau particles. Neutrinos can spontaneously transition from one flavor to another. This phenomenon, called neutrino oscillations, questions the validity of the standard model of particle physics and call for new physics. Because neutrinos are weakly interacting particles, detectors larger than the ton scale are often necessary to study them. This PhD thesis focuses on the development of a new technique for the detection of reactor antineutrinos, using the coherent elastic neutrino-nucleus scattering (CEvNS) process. Depending on the target nucleus, the CEvNS cross-section can be up to a factor 1000 larger than those of the other neutrino detection channels (inverse beta decay, neutrino-electron scattering), making it an attractive process to reduce the size of neutrino detectors and to perform precision neutrino physics. CEvNS is a promising process offering the possibility to carry out a rich experimental program, ranging from the study of the fundamental properties of the neutrino (magnetic moment, existence of additional sterile species) and the nucleus internal structure (weak charge distribution) to precision tests of the standard model of particle physics at low energies (measurement of the Weinberg angle, search for new couplings, etc). Finally, exploiting CEvNS for long range neutrino detection could also lead to useful applications, such as the detection of supernovae and the surveillance of nuclear reactors.

This PhD thesis takes place within the NUCLEUS experiment, which aims at detecting and studying CEvNS for the first time at a nuclear reactor. The CEvNS experimental signature is a very low energy nuclear recoil (< 0.1-1 keV), making conventional detection techniques ineffective to study this process. The NUCLEUS collaboration is therefore developing a new concept of cryogenic detectors achieving ultra-low energy thresholds down to 10 eV. The collaboration targets their deployment and commissioning at the Chooz nuclear power plant (France) by 2022/2023. The proposed PhD work consists in leading a detailed study and characterization of the backgrounds in this yet uncharted energy regime. This work is the main challenge to address in order to guarantee the success of the experiment, and it will lead to the first detection of CEvNS at a nuclear reactor.

In further details, the PhD student will first contribute to the development a full analysis chain for the processing of the NUCLEUS data. Background data and calibration data collected during the different stages of the experiment (cryogenic detector prototyping stage, blank assembly of the full experimental setup and integration of the full experiment at the Chooz nuclear plant) will be analyzed and compared to the predictions of a background modeling using the Geant 4 MC simulation package. The ultimate goal of this work is to quantify the background rejection performances of the NUCLEUS setup, and to end up with a detailed and comprehensive background modeling in the CEvNS region of interest (E < 1 keV). In the course of this work, a special attention will be paid to neutrons. Because they can elastically recoil on nuclei and hence perfectly mimic a CEvNS signal, neutrons are the ultimate type of background to fight against. Additionally to this work, the PhD student will also be expected to contribute to various service tasks for the collaboration: blank assembly of the NUCLEUS setup in Munich, integration and commissioning of the NUCLEUS setup at Chooz, calibration and data taking shift, etc. He/she will be hence expected to regularly travel to Chooz and Munich.

The PhD student will integrate the “low energy neutrino” group, which gather physicists from the particle physics and nuclear physics departments of the Institute of Research into the Fundamental laws of the Universe (Irfu) at CEA Paris-Saclay. Over the past decades, the team acquired a solid expertise in reactor antineutrino physics (Double Chooz, Nucifer and STEREO experiments) and in low energy antineutrino physics (CUORE, CUPID and KATRIN experiments). The PhD student will also work in an international environment, as the NUCLEUS collaboration gathers foreign partners in Germany, Austria and Italy.

LHC luminosity measurement with the ATLAS Liquid Argon Calorimeter and search for long lived massive particles

SL-DRF-20-0331

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Atlas (ATLAS)

Saclay

Contact :

Philippe Schwemling

Starting date : 01-10-2020

Contact :

Philippe Schwemling
CEA - Liste des pôles/Liste des départements/Liste des services/Atlas

33 1 69 08 85 85

Thesis supervisor :

Philippe Schwemling
CEA - Liste des pôles/Liste des départements/Liste des services/Atlas

33 1 69 08 85 85

The discovery of the Standard Model Higgs boson in 2012 is undoubtedly a bright success for the Standard Model of particle physics ? This discovery however does not bring any answer to many of the questions that are still open in cosmology and particle physics. Among others, there is the nature of drak matter and dark energy, the origin of the Higgs potential, and the fact that the Standard Model does not provide an explanation for the very small masses of the neutrinos. Natural solutions to these problems could come from the existence of new interaction types or new particles.

This is why 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. This is a factor two or three better than the precision that has been reached up to now.

LHC experiments are equipped with dedicated luminosity measurement subsystems, and several observables can be used to measure the luminosity. However, the techniques used have various stability and linearity issues, that complicate their exploitation.

After the LHC restart, foreseen in 2021, 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 by FPGAs of the digitized detector signals. Irfu is one of the key contributors to the design and the production to the necessary hardware elements, as one of the instituts in charge of the design and production of the LTDB (LAr Trigger Digitizing Board), i.e. the board that digitizes the detector analog signals and transmits them to the back-end FPGAs

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. Preliminary studies performed on a prototype trigger chain show that the 1% precision level should be reachable.

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. The spatial granularity of the information is however somewhat coarser than the granularity available to the main readout. This 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.



The neutrino nature through the study of double-beta decays of the Xenon 136 on in the PandaX-III experiment

SL-DRF-20-0284

Research field : Particle physics
Location :

Service de Physique Nucléaire (DPhN)

Laboratoire structure du nucléon (LSN) (LSN)

Saclay

Contact :

Damien NEYRET

Starting date : 01-10-2020

Contact :

Damien NEYRET
CEA - DRF/IRFU/DPhN/LSN

01 69 08 75 52

Thesis supervisor :

Damien NEYRET
CEA - DRF/IRFU/DPhN/LSN

01 69 08 75 52

Laboratory link : http://irfu.cea.fr/dphn/index.php

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

The neutrino, as the only particle of mater (fermion) without electrical charge, could be a Majorana particle, i.e. identical to its antiparticle. In this case a new phenomenon should appear for a few radioactive atomic nuclei: the neutrinoless double beta decay. The violation of the leptonic number which follows, forbidden by the Standard Model, would be a major discovery and one of the required conditions to explain the mater-antimatter asymmetry in the Universe.



The PandaX-III experiment aims to measure the kinematics of double-beta decays of Xenon 136 in a large volume of 10 bar gaseous Xenon. This experiment could detect double-beta decays without emission of neutrinos and distinguish them from backgrounds like regular double-beta decays with neutrino emission, gammas from radioactive contamination, or cosmics. These rare processes will be detected in gaseous Xenon inside large Time Projection Chambers (TPC) with a detection of ionization electrons based on Micromegas Microbulk micro-pattern gaseous detectors. The TPC will operate under a pressure of up to 10 bar. An excellent resolution of electron energy measurement and a very good reconstruction of the event topology is required to separate neutrinoless double-beta decays from the various backgrounds. A high radiological purity of the experimental set-up is also necessary to limit the gamma background contamination. This experiment will take place in the Jinping underground laboratory (Sichuan province, China) which presents the lowest residual cosmics rate in the world. A first 145kg-Xenon TPC chamber will be installed in 2020, and 5 modules will be installed in the following years to reach a level of 1t of Xenon.



Associated with the PandaX-III team at IRFU the student will participate to the development of data reconstruction algorithms by taking into account and compensating detectors imperfections like missing channels, performance inhomogeneities, etc... The compensation methods will include calibration methods and interpolations of missing data, and neural network methods of data corrections will be also evaluated. As soon as the data of the first TPC module are available the student will participate in collaboration of the other PandaX-III members to the analysis and the extraction of the physics results. In parallel he will participate to the detector R&D conducted on several types of Micromegas detectors, in order to reach 1% energy resolution at 2.5 MeV. This work will include performance measurements of the different prototypes in high pressure gaseous environment.

Advanced artificial intelligence techniques for the event filtering at the CMS detector

SL-DRF-20-1004

Research field : Particle physics
Location :

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

Systèmes Temps Réel, Electronique d’Acquisition et Microélectronique

Saclay

Contact :

Mehmet Ozgur SAHIN

Fabrice COUDERC

Starting date : 01-10-2020

Contact :

Mehmet Ozgur SAHIN
CEA - DRF/IRFU/DEDIP/STREAM

01 69 08 14 67

Thesis supervisor :

Fabrice COUDERC
CEA - DRF/IRFU/DPHP/CMS

01 69 08 86 83

After a very successful operation period crowned with the discovery of the Higgs boson, the Large Hadron Collider will undergo a luminosity upgrade where it is planned to increase the collision rate by a factor of ten. The CMS detector will also be upgraded to cope with these challenging environment and to enable a better event reconstruction, particularly with the new high-granularity calorimeters. Collecting, filtering and processing the data from these detectors will pose a significant challenge. In order to make the most out of it, the modern artificial intelligence techniques will be essential. We are looking for an enthusiastic student who will study the possible machine learning techniques that can be implemented in the Field Programable Gate Arrays (FPGA) to enable very high-speed reconstruction and filtering of this immense amount of data.



Event reconstruction and analysis in CMS using artificial intelligence

SL-DRF-20-0391

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe CMS (CMS)

Saclay

Contact :

Bruno LENZI

Starting date : 01-09-2020

Contact :

Bruno LENZI
CEA - DRF/IRFU/DPHP/CMS


Thesis supervisor :

Bruno LENZI
CEA - DRF/IRFU/DPHP/CMS


Laboratory link : http://irfu.cea.fr/dphp/

Recent developments in computer hardware and deep-learning algorithms, combined with large datasets, lead to impressive progress in artificial intelligence in the past few years. Image processing with computer vision techniques, in particular, emerged as dynamic and prolific field of research with many applications.



Although only marginally studied in high energy particle collisions, deep-learning algorithms already demonstrated the ability to perform particle and event classification, estimation of kinematic variables and anomaly detection. Those abilities are extremely useful in the analysis of the unprecedented amount of proton-proton collisions expected in the next running phases of the Large Hadron Collider (LHC) at CERN. The CMS detector will undergo major upgrades to deal with the increasing number of additional collisions per LHC bunch crossing (pileup), benefiting from more finely segmented detectors and precise timing information. Fast, robust and adaptive event processing and analysis will be the key to explore those upgrades.



The proposed PhD thesis topic focuses on the development of global and sophisticated algorithms using state-of-art machine learning techniques for particle identification, pileup rejection and finally event classification applied to the measurement of Higgs boson properties. The objective is to transfer the algorithmic knowledge gained in simple tasks to more complex ones. The successful candidate will contribute to those studies and participate in the development and testing of detector electronics for precise timing measurements with of the various CMS subsystems.
INTENSE POSITRONIUM TARGET FOR ANTIHYDROGEN PRODUCTION IN THE GBAR EXPERIMENT

SL-DRF-20-0473

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Antimatière et gravitation (GAG)

Saclay

Contact :

Patrice PEREZ

Starting date : 01-10-2020

Contact :

Patrice PEREZ
CEA - DRF/IRFU/DPhP/GAG

0169083583

Thesis supervisor :

Patrice PEREZ
CEA - DRF/IRFU/DPhP/GAG

0169083583

Description

This thesis takes place in the GBAR experiment at CERN, which aims to measure the acceleration of gravity on antihydrogen. The specificity of the experiment is to use positive antihydrogen ions to produce ultra-cold antihydrogen atoms, allowing an accurate measurement of their free fall. To produce antihydrogen ions, antiprotons ( p ) must interact on a cloud of positronium (Ps), the bound state of an electron and a positron. Two successive reactions are used:

p +Ps* -> H* + e- et H + Ps -> H+ + e- .



The amount of anti atoms and anti ions produced depends not only on the flux of antiprotons, but also on the density of the positronium target. In particular, the amount of anti ions produced by the second reaction is proportional to the square of the density of Ps. Positronium is produced by implanting positrons in a nanoporous silica in an amount proportional to the flux of positrons. The positron flux currently obtained is about 5 x 1E8 in 10 minutes, already representing a factor of 10 improvement over the world record.

The purpose of the thesis is to gain up to another factor 100 on this flux and measure the density of the corresponding positronium target in order to measure the effective section of the first reaction.



Group/lab/supervision

The host team includes six physicists, including the spokesperson for the collaboration, and a thesis student. GBAR is an international collaboration involving about 50 physicists from 18 laboratories.



Work proposed

Important factors can be gained in the accumulation of positrons in Penning-Malmberg traps. The technique to be used will take into account the fact that the initial positron beam in GBAR is pulsed, and will do without the buffer gas used in the first trap. The density of the Ps target can be measured either by using gamma detectors or by characterizing this target with the Ps excitation laser beam. The measurement of the cross-section will follow a thesis during which the signal and background noise were studied by simulation. The restart of the antiproton beam is scheduled for mid 2021 for periods of about six months per year. During periods without antiprotons, a proton beam will be used to study the symmetric reaction producing hydrogen. This work will cover the optimization of trapping, the understanding of detectors, the excitation laser, as well as simulations of the experiment, estimation of efficiencies, background noise, calculation of cross-sections and comparison with theoretical predictions. The results will be presented at the conference and published.



Training and skills required

The student must have training in experimental corpuscular physics. He will need to acquire programming and instrumentation skills, and will be able to work in a team environment.



Skills acquired

At the end of the thesis, the student will have acquired knowledge in fundamental physics (particle and atomic physics), instrumentation (ultra-high vacuum techniques, trace detectors, lasers, electronics) and programming. He will have worked in a very competitive international environment.



Collaborations/Partnerships

The realization of the experiment is conducted as an international project. Much of the work will be done at CERN.



Contacts

Scientific :

P. Pérez (thesis supervisor), L. Liszkay (responsible for positron and positronium production), D. van der Werf (trapping).

DETECTORS FOR TIME-OF-FLIGHT PET IMAGING WITH HIGH SPATIAL RESOLUTION

SL-DRF-20-0397

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Santé et Energie (GSE)

Saclay

Contact :

Dominique YVON

Viatcheslav SHARYY

Starting date : 01-10-2020

Contact :

Dominique YVON
CEA - DRF/IRFU/DPHP

01 6908 3625

Thesis supervisor :

Viatcheslav SHARYY
CEA - DRF/IRFU/DPHP/DO

0169086129

Personal web page : http://irfu.cea.fr/Pisp/dominique.yvon/

Laboratory link : http://irfu.cea.fr/Spp/en/Phocea/Vie_des_labos/Ast/ast_technique.php?id_ast=3937

In this thesis we propose to contribute to an ambitious detector based on Cherenkov/Scintillating crystals. We have selected technologies that are particularly effective for PET imaging. The principles of the detector are patented. They will allow one to produce neurological PET with highly improved performances. The device uses advanced particles detector technologies: a dense scintillator crystal, micro-channel plate photomultipliers, gigahertz bandwidth amplifiers and fast data acquisition modules (WaveCatcher, SAMPIC). Data processing will involve Monté-Carlo simulations and data analysis based on GATE/Geant4 and Root C++ software libraries.



Context:

Positron emission tomography (PET) is a nuclear imaging technique widely used in oncology and neurobiological research. Decay of the radioactive tracer emits positrons, which annihilate in the nearby tissue. Two gamma quanta of 511 keV energy are produced by positron annihilation and allow one to reconstruct the annihilation vertex and distribution of the tracer activity in the body of the patient.

The precise determination of the position of the positron annihilation vertex is important for an accurate image reconstruction with a good contrast. In particular, it is useful for neuroimaging studies of brain and for pre-clinical studies with animal models (rodents).



Supervision:

You will calibrate and optimize the detector prototypes and analyze the measured data. Your will be focussing on detector time and spatial resolution optimization. This will involve many skills of an instrument scientist : fast photo-detection, fast electronics read-out (analog and digital) with picosecond precision, hardware and detector simulations with GEANT4 and GATE software.



Requirements:

Knowledge in physics of particle interaction with matter, radioactivity and particle detector principles, a vocation for instrumental (hardware) work, data analysis are mandatory. Being comfortable in programming, having a background in Gate/Geant4 simulation and C++ will be an asset.



Acquired skills:

You will acquire skills in particle detector instrumentation, simulation of ionizing radiation detectors, photo-detection, implementation, operation of fast digitizing electronics, and data analysis.



Contacts:

Dominique Yvon : dominique.yvon@cea.fr

Viatcheslav Sharyy : viatcheslav.sharyy@cea.fr

T2K Near Detector performance and CP violation measurement in neutrino oscillations

SL-DRF-20-0326

Research field : Particle physics
Location :

Service de Physique des Particules (DPHP)

Groupe Neutrinos Accélérateurs (GNA)

Saclay

Contact :

Samira Hassani

Sandrine EMERY

Starting date : 01-10-2020

Contact :

Samira Hassani
CEA - DRF/IRFU/SPP/Atlas

0169087226

Thesis supervisor :

Sandrine EMERY
CEA - DSM/IRFU/SPP/TK2

0169081461

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 8of 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?



The long-baseline experiments T2HK and DUNE, will measure neutrino oscillations with high statistics, requiring a control of the systematic uncertainties at 1-2% level, the most complex ones being the modeling of the neutrino flux and of neutrino-nucleus interactions. Thus, the role of the near detectors and the neutrino-nucleus cross-section measurements are becoming crucial. T2K experiment is opening the way to the next generation, by improving the understanding of the systematic uncertainties and exercising new performing detector and analysis techniques. The final aim is the discovery of CP-violation in the leptonic sector, the definitive identification of the mass ordering through matter effects and the precise measurement of atmospheric oscillation parameters.



The T2K collaboration is preparing an upgrade of the Near Detector (ND280), to be installed in 2021, in order to improve the Near Detector performance to measure the neutrino interaction rate and thus constrain the neutrino interaction cross sections so that the systematic uncertainty in the number of predicted events at the T2K far detector, Super-Kamiokande, will be reduced to about 4% (from about 8% as of today). This will allow to improve the physics reach of the T2K project, enabling a 3sigma exclusion of CP conservation.

The upgrade of the ND280 detector consists in the addition of a highly granular scintillator detector, the Super-FGD, sandwiched between two High-Angle Time Projection Chamber (TPC). The new TPCs will be readout by resistive Micromegas detectors and instrumented with a compact and light field cage. The SuperFGD will enable much lower threshold for the particle reconstruction (notably for protons) and, for the first time in T2K, the measurement of neutrons. 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 and 2019 at CERN and DESY test-beams validating the detector technologies and their performances.



The IRFU group is heavily involved in the TPC project, especially in Micromegas detectors production and tests. The first part of the thesis will be devoted to TPC data analyses. The student will contribute to the test-beam data taking and analysis foreseen in October 2020. The work will focus on the characterization of the Micromegas resistivity and the consequent spatial and energy (dE/dx) resolution. The IRFU group is developing a quantitative model of the resistivity calculation which will be included in the simulation. A precise reconstruction algorithm will be tuned, based on the so-called Pad Response Function approach. This will be the first detailed measurement of the resistivity, uniformity and the corresponding resolution of resistive MicroMegas in a complete detector with large surfaces and thus will have an important impact for the validation of such technology for further development.

The detector construction for the ND280 Upgrade will be performed in 2019-2020, for an installation in Japan in 2021. The student will contribute also to the installation and the commissioning of the ND280 detector.



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 data samples for the analysis, 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 from neutrino interactions on nuclei, which are completely missing in the present analysis. In parallel, the theoretical systematic uncertainties will need to be reevaluated based on the new exclusive models of neutrino-nucleus interactions.

 

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