Liste des offres de thèses du laboratoire.

Atlas
Etude des propriétés du boson de Higgs avec le détecteur ATLAS au LHC
Directeur de thèse :
Emmanuel MONNIER - +33 4 91 82 72 69 - monnier@cppm.in2p3.fr
Description :

English Version: Physics at the Large Hadron Collider (LHC) at CERN (European Organization for Nuclear Research) is the high priority research field of the Particle Physics community worldwide. ATLAS is one of the two general purpose experiments installed at the LHC that discovered a Higgs boson in July 2012, key piece for the understanding of the fundamental interactions and the origin of elementary particle mass. Its physics program extends beyond Higgs property measurements to the search for signs of physics beyond the Standard Model of particle physics.

The ATLAS group of the Centre de Physique des Particules de Marseille (CPPM) is deeply involved in this scientific program, in particular linked to its expertise of the electromagnetic calorimeter. The latter is a key component for the identification and energy measurement of electrons and photons, which were at the core of the Higgs boson discovery. It is also at the forefront of this boson studies and of the supersymmetry searches in the ongoing data taking campaign, so called Run 2, with major consequences in several analyses with leptons in their final states. Moreover, for the upgrade of the accelerator performances foreseen in 2021, this calorimeter has a major ongoing development program to dramatically upgrade its trigger and readout to which the CPPM group actively contributes.

In the Standard Model, the Higgs boson is highly coupled to the top quark, the known particle with the largest mass. The only way to directly measure this Higgs-top coupling (called top Yukawa coupling) is to observe the associated production of a Higgs boson with top quarks. This will be accessible for the first time with the Run 2 data that are taken since 2015 and until 2018. This key measurement, and more generally the Higgs properties studies are of high importance since they would allow to confirm that the observed boson is the Standard Model Higgs boson, or could reveal New Physics.

The goal of this thesis is on the one hand to exploit the Run 2 data set to get the best sensitivity on the Higgs property measurements and in particular the Yukawa coupling. The student will focus on the Higgs property measurement in multilepton final states (electron or muon). The Run 2 data taking conditions at the LHC (proton-proton collision center of mass energy increased to 13 TeV, high luminosity) are particularly suited for these measurements. The sensitivity to the sub-dominant Higgs production modes  particularly its associated production with top quarks  is increased, allowing for refined measurements of the Higgs boson properties. On the other hand and in parallel, the student will also contribute to the electromagnetic calorimeter upgrade, and in particular, to the study of its upgraded configuration, first exploiting data taken with a prototype installed for the 2018 data taking, then contributing to the installation and commissioning of its final system, and finally to its validation and performances assessment with the first Run 3 data in 2021.

In this framework, the student will have to do frequent stays at CERN and the research work will combine physics analysis on real and simulated data as well as studies and operation of experimental systems.

French Version: La physique auprès du Large Hadron Collider (LHC) du Centre Européen de Recherche Nucléaire (CERN) constitue aujourd'hui l'axe de recherche prioritaire de la communauté mondiale en physique des particules. ATLAS, l'une des deux expériences généralistes installées auprès de cet accélérateur, a découvert un boson de Higgs en juillet 2012, pièce essentielle pour la compréhension des interactions fondamentales et en particulier l'origine de la masse. Son programme de physique est néanmoins plus vaste et s'étend à l'étude des propriétés du boson de Higgs et plus généralement à l'obtention des premiers signes de physique au-delà du Modèle Standard de la physique des particules.

Le groupe ATLAS du Centre de Physique des Particules de Marseille (CPPM) est fortement impliqué dans ce programme scientifique, avec notamment une expertise liée au calorimètre électromagnétique. Ce dernier est un élément clé pour l'identification et la mesure de l'énergie des électrons et des photons, qui ont fait le succès de la découverte du boson de Higgs. Il est également en pointe sur l'étude de ce boson et la recherche de supersymétrie dans la campagne de prise de données actuelle, dite « Run 2 », avec des implications majeures dans plusieurs analyses avec des leptons dans l'état final. De plus, en vue de l'amélioration des performances de l'accélérateur prévue pour 2021, ce calorimètre fait l'objet d'un important programme d'évolution de son système de lecture et de déclenchement auquel participe activement le groupe du CPPM.

Dans le Modèle Standard, le boson de Higgs se couple préférentiellement avec le quark top, particule élémentaire la plus massive jamais découverte. Le seul moyen de mesurer directement ce couplage (dit couplage de Yukawa du top) est d'observer la production associée du Higgs avec des quarks top. Cela sera accessible pour la première fois avec les données du « Run 2 » qui sont prises depuis 2015 jusqu'en 2018. Cette mesure et plus généralement, l'étude des propriétés du boson de Higgs sont très importantes, car elles peuvent confirmer que le boson observé est bien le boson de Higgs du Modèle Standard ou pourrait révéler de la nouvelle physique.

Le sujet de cette thèse est d'une part d'exploiter la prise de données du « Run 2 » pour obtenir la meilleure sensibilité sur ces mesures des propriétés du boson de Higgs, en particulier sur la mesure du couplage de Yukawa. L'étudiant(e) axera son travail d'analyse sur la mesure des propriétés du boson de Higgs dans les états finals à plusieurs leptons (électrons ou muons). Les conditions de la prise de données « Run 2 » au LHC (énergie dans le centre de masse des collisions protons-protons accrue à 13 TeV, grande luminosité) sont particulièrement favorables pour ces mesures. En effet, la sensibilité aux productions sous-dominantes du boson de Higgs  notamment en association avec une paire de quarks top - est accrue, permettant des mesures plus fines des propriétés du boson de Higgs. D'autre part et en parallèle, l'étudiant contribuera au programme d'amélioration du calorimètre électromagnétique, et en particulier, étudiera ses performances dans sa configuration optimisée, d'abord en exploitant les données prises avec un prototype installé sur le détecteur pour la prise de données 2018, puis en contribuant à l'installation et à la mise en uvre du système final et enfin à sa qualification et à l'établissement de ses performances avec les premières données du Run 3 en 2021.

Dans ce cadre l'étudiant sera amené à effectuer de nombreux séjours au CERN, et son travail de recherche combinera des analyses de physique (sur données et simulation) ainsi que l'étude et la mise en uvre de systèmes expérimentaux.

Mots clefs :
Physique des particules
Code :
Doctorat-1821-AT-01
Discovering the Higgs boson in the ttH channel with the ATLAS experiment at the LHC
Directeur de thèse :
Arnaud Duperrin - (+33) 04 91 82 72 00 - duperrin@cppm.in2p3.fr - -
Description :

The LHC will undergo long period shutdowns between 2019 and 2021 and around 2024. The ATLAS detector will be upgraded to enhance its performance at the higher luminosity. The upgrade of the ATLAS detector and of the LHC collider is necessary in order to maintain scientific progress and to explore its full capacity. This thesis work includes a contribution to the ongoing Research and Development efforts at CPPM related to the upgrade of the detector. In particular, the student will be involved in tracking and b-tagging performance studies in order to guide the design of the new pixel detector currently under development.

The discovery of the Higgs boson in 2012 has confirmed the Standard Model (SM) as an extremely successful theory of elementary particles and their interactions via three of the four fundamental forces. Still, the SM fails to account for key aspects of our universe and is unable to provide an explanation for its numerous free parameters and their hierarchical pattern, characterised by a gigantic and unnatural gap between the Higgs boson mass and the scale of quantum gravity.

Most theoretical attempts to solve these puzzles invoke the existence of physics Beyond the Standard Model (BSM), and in the pletora of BSM models that have been put forward the Higgs boson and the top quark typically play a central role. This renders direct tests of top-Higgs interactions one of the most promising tools to challenge the SM and to find possible evidence for BSM physics. This thesis will focus on the ttH(bb) process for the physics analysis, profiting from the large branching fraction of the Higgs boson to a pair of bottom quarks. The ATLAS CPPM expertise is very strong in this area with already several theses defenses on this topic.

Bibliography: Evidence for ttH production with the ATLAS detector https://indico.cern.ch/event/656771/ and https://cds.cern.ch/record/2291393/files/ATLAS-CONF-2017-076.pdf

Mots clefs :
Physique des particules
Code :
Doctorat-1821-AT-02
Km3NeT
Study of Neutrino Mass Ordering with data of the KM3NeT/ORCA deep sea Neutrino Detector
Directeur de thèse :
Paschal COYLE - office: 0491827253, portable: 0675713799 - coyle@cppm.in2p3.fr
Description :

KM3NeT/ORCA (Oscillation Research with Cosmics in the Abyss) is a deep sea neutrino telescope currently under construction at a depth of 2500m in the Mediterranean Sea off the coast of Toulon. ORCA is optimised for the detection of low energy (3-100 GeV) atmospheric neutrinos and will allow precision studies of neutrino properties including the neutrino mass ordering. ORCA is part of the multisite KM3NeT research infrastructure, which also incorporates a second telescope array (in Sicily) optimised for the detection of high-energy cosmic neutrinos. The first ORCA detection strings have recently been deployed and are providing high quality data.

During this thesis, at the Centre de Physique des Particules de Marseille, the student will develop the analysis methods for a preliminary estimation of the neutrino mass ordering with the first years of ORCA data.

There is also the possibility of a related M2 stage on this project.

Mots clefs :
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Code :
Doctorat-1821-KM-01
LHCb
Search for the rare B decays with $\tau$ leptons in the final state
Directeur de thèse :
Giampiero Mancinelli and Julien Cogan - 0491827675 - giampi@cppm.in2p3.fr , cogan@cppm.in2p3.fr
Description :

Over the past few years, several measurements related to flavor-changing neutral current transitions have shown deviations from the Standard Model (SM) expectations. These deviations build up a tension at the 4-5$\sigma$ level with respect to the Standard Model (SM) and they are currently the only indications of new physics coming from the CERN Large Hadron Collider (LHC) [1,2]. The consistent picture which is forming points towards violation of Lepton Flavour Universality (LFU), one of the building blocks of the SM. LFU violation is hence becoming an extremely hot topic on which LHCb should be able to shed light in the forthcoming years. The very rare decays of $B_(s)$ mesons into leptons are key channels to indirectly constraint the new physics phase space. The muonic final states have been widely studied by different experiments but the decays into tau leptons are still very unconstrained, because of the difficulty in reconstructing taus.

The LHCb experiment, one of the 4 large experiments operating at the LHC, is dedicated to heavy flavor physics. During the LHC Run I (2011-2012), it has collected about 3 fb$^{-1}$ of proton-proton interactions, gathering the largest sample of B mesons ever recorded, and thus it is a unique place to look for rare or forbidden decays.

After taking a leading role in the first observation of the $B^0_s \to \mu^+ \mu^-$ decay, after a 20 years search (published in Nature in 2015 [3]), the LHCb team has published the first limit on $B^0_s \to \tau^+ \tau^-$ in 2017 [4] with the Run I data. The goal of this thesis project is to exploit the full LHCb data-set (currently including 3fb$^{-1}$ of Run II data as well) to carry-out searches for several $B$ decay modes with taus in the final state : $B^0 \to K^{*0} \tau^+\ tau^-$ , $B^0_{(s)} \to \tau^+\ tau^-$ and $B^0_{(s)} \to \tau \mu$ . The development and optimization of new reconstruction algorithms and analysis techniques are envisaged, as well as frequent trips to CERN.

References: (1)arXiv:1704.05340 (2)Eur. Phys. J. C (2017) 77: 377 (3)arXiv:1411.4413 (4)arXiv:1703.02508

Mots clefs :
Physique des particules
Code :
Doctorat-1821-LH-01