Liste des offres de thèses du laboratoire.

DarkSide
Recherche directe de Matière Noire avec le détecteur DarkSide-20k / Direct search for Dark Matter with the DarkSide-20k experiment
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Directeur de thèse :
Fabrice Hubaut, Isabelle Wingerter-Seez - 04 91 82 72 51 - hubaut@in2p3.fr , wingerter-seez@cppm.in2p3.fr
Description :

La matière noire est une des grandes énigmes actuelles de la physique fondamentale. En effet, sa contribution à la masse totale de l'Univers est de 85% mais elle ne peut être expliquée dans le cadre du Modèle Standard de la physique des particules (MS). Plusieurs candidats existent pourtant dans les théories au-delà du MS : c'est le cas du WIMP (Weakly Interacting Massive Particle), un des candidats les mieux motivés car il permet de résoudre le problème de stabilité de la masse du boson de Higgs dans le MS.


Si la masse du WIMP est O(100) GeV, il a une densité compatible avec les observations cosmologiques. Les expériences recherchant la matière noire utilisent ainsi le halo de notre galaxie comme source potentielle de WIMPs. Depuis 2010, la technologie de détection la plus performante repose sur la mesure de la lumière de scintillation qui serait émise lors de la diffusion d'un WIMP sur un atome de liquide noble - argon ou xénon. L'expérience DarkSide-20k, qui sera installée à 2 km sous terre au laboratoire du Gran Sasso en Italie, est la deuxième génération de détecteurs à argon liquide. Elle utilisera une cuve cubique de 8 m de côté remplie de 50 tonnes d'argon, lue par 200 000 photomultiplicateurs au Silicium. Cela lui permet d'avoir l'une des meilleures capacités de découverte des WIMPs au niveau mondial. La prise de données devrait commencer en 2024. La phase actuelle est consacrée à la réalisation et l'exploitation d'un prototype au CERN, de taille réduite par rapport au détecteur final, mais équipé de la même technologie que DarkSide-20k.


Le sujet de cette thèse est d'effectuer une calibration précise du détecteur afin d'optimiser l'analyse des premières données. Un premier axe consistera à participer à la mise en place et à l'exploitation du système de calibration conçu au CPPM, basé sur des sources radioactives imitant le signal et le bruit de fond. En parallèle, l'étudiant(e) améliorera les algorithmes de reconstruction des données en utilisant des techniques basées sur l'intelligence artificielle (e.g. réseaux de neurones), afin d'optimiser la séparation du signal et du bruit de fond. Ces activités apportent une formation complète en physique des particules, incluant les aspects instrumentaux, software et analyse de données. Elles seront intégrées à la préparation des premières prises de données scientifiques prévues en 2024.


Dans ce cadre l'étudiant sera amené à effectuer des séjours au CERN at au Gran Sasso.


Plus de détails sur le groupe Matière Noire du CPPM : https://www.cppm.in2p3.fr/web/fr/recherche/physique_particules/#Mati%C3%A8re%20Noire



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Dark matter is today one of the main puzzles in fundamental physics. Indeed, its contribution to the total mass of the Universe is 85%, but it cannot be explained in the framework of the Standard Model (SM) of particle physics. Several candidates exist in theories beyond the SM, and the WIMP (Weakly Interacting Massive Particle) is one of the best motivated of these candidates, as it allows to also solve the SM hierarchy problem (stability of the Higgs boson mass).


If the WIMP mass is O(100) GeV, its density in the Universe is compatible with cosmological observations. Experiments searching directly for dark matter thus use our galaxy halo as a potential source of WIMPs. Since 2010, the most sensitive technology is based on the measurement of the scintillation light from the scattering of a WIMP on a liquid noble atom – argon or xenon. The DarkSide-20k experiment, which will be installed 2 km underground in the Gran Sasso laboratory in Italy, is the second generation of liquid argon detectors. It will use a cubic cryostat of 8 m side filled with 50 tons of highly purified argon, read out by 200,000 silicon photomultipliers. This allows to have a world leading discovery potential for WIMPs. The data taking should start in 2024. The actual work is dedicated to the realization and the exploitation of a prototype, of reduced size compared to the final detector but using all technologies foreseen for DarkSide-20k.


The goal of this thesis is to perform a precise calibration of the detector to optimize the first data analysis. A first axis will consist in participating to the set-up and the exploitation of the calibration system designed at CPPM, based on radioactive sources mimicking signal and backgrounds. In parallel, the student will improve data reconstruction algorithms by using artificial intelligence techniques (e.g. neural networks), to optimize the separation between signal and backgrounds. These activities bring a complete education in particle physics, including instrumental aspects, software and data analysis. They will be integrated to the preparation of the first scientific data takings foreseen in 2024.


In this framework, the student will have to do stays at CERN and Gran Sasso.


More details about the CPPM Dark Matter team : https://www.cppm.in2p3.fr/web/en/research/particle_physics/#Dark%20Matter


Mots clefs :
Physique des particules
Code :
Doctorat-2124-DS-01
LHCb
Test of Lepton Flavour Universality using BDτν B \to D^*\tau\nu decays at LHCb
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Directeur de thèse :
Olivier Leroy - 04 91 82 76 05 - Olivier.Leroy@in2p3.fr
Description :

Applications are invited for a PhD student position at the Centre de Physique des Particules de Marseille (CPPM), France. Applicants must hold a Master degree (or equivalent) in Particle Physics, or expect to obtain such a degree by September 2021. The PhD contract will start on October 1st, 2021, for 3 years. The deadline for application is March 15th, 2021, but early applications are encouraged.


LHCb is one of the four major experiments installed at the largest proton-proton collider ever built, the LHC, at Cern, Geneva, Switzerland. The experiment is dedicated to the search for Physics Beyond the Standard Model (BSM) studying beauty and charm hadrons. Since the beginning of data taking in 2010, LHCb has accumulated the largest sample of b-hadrons ever collected and published hundreds of world-leading measurements. The CPPM LHCb group is deeply involved in the experiment since its beginning.


In the past few years, two intriguing anomalies have shown up in the flavour sector. One related to the bs b \to s\ell\ell flavour changing neutral current and another one in the bcτν b \to c\tau\nu charged current. Both effects are 4σ \sim4\sigma away from the Standard Model (SM) expectation.


Concerning the second effect, the measured quantities are the ratios of branching fractions R(D())=BR(BD()τν)/BR(BD()ν) R(D(*)) = BR(B \to D^{(*)}\tau\nu) / BR(B \to D^{(*)}\ell \nu) , (=μ,e) (\ell = \mu,e) . In the Standard Model, the only difference between the numerator and the denominator is the lepton mass. When combining the results of the BaBar, Belle and LHCb experiments, the measurements appear to be 3.8σ 3.8\sigma away from their SM expectation. This is a striking hint of violation of the lepton flavour universality which clearly needs to be checked by all means.


The student will study the BD()τν B \to D^{(*)}\tau\nu channel, where the τ \tau lepton is reconstructed into its 3 pions final state (π+ππ+ν) (\pi^+\pi^-\pi^+\nu) . In addition to a measurement of the branching ratio, the student will perform an angular analysis of the decay products which will bring new sensitivity to BSM effects. She/he will use the full run1 and run2 data sets (2011-2018), to achieve an un-precedented precision and hopefully clarify the current situation. The student will often travel to Cern, to participate to run3 data taking and to present her/his results.


Applicant profile: \bf Applicant~profile: The ideal candidate will have some experience in experimental particle physics, a strong interest in data analysis and good software skills (C++, python, ROOT). She/he should have excellent academic background. Applications with a detailed CV, a motivation letter and 2 recommendation letters should be sent to: Olivier.Leroy@in2p3.fr


Keywords: \bf Keywords: Experimental High Energy Physics, LHCb, Flavour physics, New Physics, Beyond the Standard Model searches. LFU, Lepton Flavour Universality, Flavour anomalies, Data analysis.


References: \bf References:
- Measurement of BDτν B \to D^*\tau\nu branching fraction using three-prong τ \tau decays, Phys. Rev. D97, 072013 (2018).
- Model-independent method for measuring the angular coefficients of BDτν B \to D^*\tau\nu decays, JHEP 11 (2019) 133


Mots clefs :
Physique des particules
Code :
Doctorat-2124-LH-01
Renoir
Cross-correlation between CMB observables and cosmic voids in large galaxy surveys / Analyse croisée entre les observables du CMB et les vides cosmiques dans les grandes relevés de galaxies
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Directeur de thèse :
Stéphanie ESCOFFIER - 04 91 82 76 64 - escoffier@cppm.in2p3.fr
Description :

Description: The various observations of the Universe have been indicating for twenty years now that the expansion of the Universe is accelerating. The standard model of cosmology, known as the LCDM model, describes the Universe as composed of 27% dark matter and 68% dark energy. Understanding the nature of these two energy components remains one of the greatest challenges in contemporary physics. Next-generation galaxy surveys, such as Euclid or DESI, will make it possible to measure several tens of millions of galaxy spectra in the coming decade and tighten constraints on the cosmological model, or probe its alternatives like modified gravity models.


The most promising tools to constrain dark energy and gravity properties are based on the observation of large structures in the Universe. The structure of the Universe also reveals the presence of large under-dense regions, enclosed by filaments of matter. These cosmic voids, which occupy nearly 80% of the volume of the Universe, contain very few matter, and are therefore an ideal laboratory for testing dark energy scenarios.


The subject of the thesis is to extract the integrated Sachs-Wolfe (ISW) signal by cross-correlating cosmic voids with Cosmic Microwave Background (CMB). Indeed the time evolution of gravitational potentials imprints secondary anisotropies in the CMB, in addition to the primordial CMB anisotropies generated near the last scattering surface. These additional anisotropies are caused by gravitational interactions of CMB photons with the growing cosmic large-scale structure. The ISW signal is challenging to measure since it is very weak compared to primordial CMB photons. We propose here to identify cosmic voids in large spectroscopic surveys like DESI and Euclid and study how they can contribute to cold regions in the CMB temperature pattern. A focus will be given on superstructures, by stacking cosmic voids in a given direction or by identifying supervoids.


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Résumé: Les différentes observations de l'Univers indiquent depuis près de vingt ans que l'expansion de l'Univers s'accélère. Le modèle standard de la cosmologie, connu sous le nom de modèle LCDM, décrit l'Univers comme étant composé de 27% de matière noire et de 68% d'énergie noire. La compréhension de la nature de ces deux composantes énergétiques reste l'un des plus grands défis de la physique contemporaine. Les sondages spectroscopiques de galaxies de la prochaine génération, tels que Euclid ou DESI, permettront de mesurer plusieurs dizaines de millions de spectres de galaxies au cours de la prochaine décennie et de resserrer les contraintes sur le modèle cosmologique, ou de sonder ses alternatives comme les modèles de gravité modifiés.


Les outils les plus prometteurs pour contraindre l'énergie sombre et les propriétés de la gravité sont basés sur l'observation de grandes structures dans l'Univers. La structure de l'Univers révèle également la présence de grandes régions sous-denses, cloisonnées par des filaments de matière. Ces vides cosmiques, qui occupent près de 80 % du volume de l'Univers, contiennent très peu de matière, et constituent donc un laboratoire idéal pour tester des scénarios d'énergie sombre.


Le sujet de la thèse consiste à extraire le signal intégré de Sachs-Wolfe (ISW) par corrélation croisée des vides cosmiques avec le fond diffus cosmologique (CMB). En effet, l'évolution temporelle des potentiels gravitationnels imprime des anisotropies secondaires dans le CMB, en plus des anisotropies primordiales du CMB générées près de la dernière surface de diffusion. Ces anisotropies supplémentaires sont causées par les interactions gravitationnelles des photons du CMB avec la structure cosmique croissante à grande échelle. Le signal ISW est difficile à mesurer car il est très faible comparé aux photons CMB primordiaux. Nous proposons ici d'identifier les vides cosmiques dans les grands relevés spectroscopiques comme DESI et Euclid et d'étudier comment ils peuvent contribuer aux régions froides identifiées dans la carte de température du CMB. L'accent sera mis sur les superstructures, en empilant les vides cosmiques dans une direction donnée ou en identifiant les supervides.


Mots clefs :
Cosmologie observationnelle
Code :
Doctorat-2124-RE-02
Constraints on gravity by tomographic galaxy clustering with Euclid data
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Directeur de thèse :
GILLARD William - Escoffier Stephanie - 0491827667 - gillard@cppmin2p3.fr
Description :

The various observations of the Universe have been indicating for twenty years now that the expansion of the Universe is accelerating. The standard model of cosmology, known as the CDM model, describes the Universe as composed of 27% dark matter and 68% dark energy. Understanding the nature of these two energy components remains one of the greatest challenges in contemporary physics. The future Euclid space mission is dedicated to the study of dark energy and dark matter in the Universe and to test gravity on cosmological scales. Euclid was selected by the European Space Agency (ESA) in 2011 and will be launched in 2022 to probe the Universe over a 6 yearperiod. These data will revolutionize our ability to map the Universe and better understand the nature of dark energy or put Einstein's General Relativity (GR) in default. Two instruments will be embarked on board Euclid, the Near Infrared Spectrometer and Photometer (NISP) and the visible imager (VIS). The spectroscopic survey with the NISP instrument will target fifty millions of galaxies in the redshift range 0.9 < z < 1.8. The photometric survey will get the image and photometric redshift of two billions of galaxies down to a magnitude of 24.5 AB covering the redshift range 0 < z < 2.5. The subject of the thesis is to measure the galaxy clustering from the Euclid photometric catalog using a tomographic approach. The tomographic approach (2D) has several advantages compared to the standard 3D mapping. On the one hand, the number of observed objects is two orders of magnitude larger, since 2 billion galaxies are expected in imaging compared to the 50 million galaxies expected in spectroscopy. The division into several tens of slices in redshift makes it possible to keep a competitive statistic in each slice. On the other hand, the angular approach does not require fiducial cosmology for the conversion of distances, which makes it possible to constrain the cosmological models as cleanly as possible. The interest of applying this method to Euclid data is to take advantage of the double photometric/spectroscopic observation on the same fields to calibrate the photo-z. The first step of the thesis work will consist in calibrating the photometric redshifts (photo-z) of Euclid from the spectroscopic sample. This step will be done first from the Euclid Flagship simulation which contains more than 3 million objects. A machine learning approach will be considered. Then the angular clustering tools will be developed in order to extract the clustering signal from the photometric samples. This analysis will require the optimization of the processing chain in order to be able to process more than a thousand mocks for the calculation of covariance matrices. The PhD student will be member of the Euclid Consortium, with full access to Euclid data.


Keywords : Cosmology, Dark Energy, Dark Matter, General Relativity, Galaxy Clusturing, BAO, Data Analyses, Tomograpgy, Big Data, Deep Learning, EUCLID, NISP, Photometry, Spectroscopy


Applicant profile : Master in fundamental physics or astrophysics. Interest for cosmology and machine learning tools. Programming skills (python, C++), strong motivation, ability to work in teams and in large collaborations are highly recommanded.


Mots clefs :
Cosmologie observationnelle
Code :
Doctorat-2124-RE-01