Recherche d'événements double-beta sans émission de neutrinos grâce à une TPC de Xénon à haute pression lue par détection Micromegas auprès de l'expérience PandaX-III

par Benjamin Manier

Projet de thèse en Physique des particules

Sous la direction de Damien Neyret.

Thèses en préparation à Paris Saclay , dans le cadre de École doctorale Particules, Hadrons, Énergie, Noyau, Instrumentation, Imagerie, Cosmos et Simulation (Orsay, Essonne) , en partenariat avec DSM-Institut de Recherche sur les lois fondamentales de l'Univers (Irfu) (laboratoire) et de Université Paris-Sud (établissement de préparation de la thèse) depuis le 30-09-2017 .

  • Titre traduit

    Search for neutrinoless double-beta events in a high pressure Xenon TPC with Micromegas detection at the PandaX-III experiment

  • Résumé

    The neutrino, as the only particle of mater without electrical charge, could be a Majorana particle, i.e. identical to its antiparticle. In this case a new phenomenon would appear for a few radioactive isotopes: 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 experiment proposed by the PandaX-III collaboration 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 usual 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 micro-pattern gaseous detectors. This experiment will take place in the Jin Ping underground laboratory (Sichuan, China) which presents the lowest residual cosmics rate in the world. A first 200kg-Xenon TPC chamber will be installed from end of 2017, and 5 modules will be installed up to 2022 to reach a level of 1t of Xenon. An excellent resolution of electron energy measurement, and a very good radiological purity of the experimental set-up will be required in order to separate neutrinoless double-beta decays from the different backgrounds. Associated with the PandaX-III team at SPhN and SEDI (detector, electronics and computing laboratory) the student will participate to the development of high pressure Micromegas detectors with high energy resolution and their associated electronics. R&D will be conducted on several types of Micromegas detectors like Microbulk types or bulk Micromegas with very thin meshes, in order to reach 1% energy resolution at 2 MeV. This work will include performance measurements and extractions in association with our partners at Zaragoza and Shanghai universities. In parallel the student will work on algorithms of TPC data reconstruction and to determine the characteristics of double-beta decays and background events, in order to recognize and separate the two kinds of events. Test set-up data as well as Monte Carlo simulations will be studied for that goal. These developments will be used for the analysis of the first data of the PandaX-III experiment from mid-2018 in order to determine a first limit on the production of neutrinoless double-beta decays.