Thesis

Is the neutrino its own antiparticle? - Probing the nature of the neutrino with the LZ dark matter detector

• Call:

  IDPASC Portugal - PHD Programme 2019

• Academic Year:

  2019 / 2020

• Domains:

  Experimental Particle Physics | Astroparticle Physics

• Supervisor:

  Alexandre Lindote

• Co-Supervisor:

  Claudio Frederico Pascoal da Silva

• Institution:

  Universidade de Coimbra

• Host Institution:

  Laboratório de Instrumentação e Física Experimental de Partículas

• Abstract:

  Over the last two decades, the neutrino physics field has been very active, especially after the discovery of the neutrino flavour oscillations by the Super-Kamiokande and SNO experiments (Nobel prize 2015) and confirmed by many other experiments. Due to the weak interaction of the neutrinos with the matter, many of their properties are still not well known, such as their absolute mass, their mass hierarchy, the possible existence of sterile neutrinos, their magnetic moment, etc. LZ is a 10-tonne dual-phase liquid xenon detector designed to look for WIMP dark matter particles, the biggest ever built using this technology. With the protection offered by the outer layers of xenon, the 5 tonnes of the inner region of LZ will be an extraordinarily low background place, allowing to improve the current best sensitivity to WIMPs by a factor of more than 100. But this extraordinarily quiet “laboratory” can be used to study other important physics processes beyond dark matter search such as neutrino physics. Rare nuclear processes during which two neutrinos are emitted simultaneously can be used to probe some of the neutrino properties, such as double beta decay (2νββ), double electron capture (2ν2EC) and the mixed mode with positron emission 2νECβ+. Neutrinoless versions of these decays are not allowed as they would violate the conservation of the lepton number, and thus their observation would be evidence of new physics beyond the Standard Model and the proof that neutrinos are Majorana particles (i.e., they are their own antiparticles), while providing information about the neutrino mass hierarchy and effective mass. This is one of the most interesting topics in modern physics, with several experiments around the world dedicated to look for such forbidden decays in various elements (e.g. Te-130 in SNO+ and CUORE, Ge-76 in GERDA and MAJORANA). Xenon is particularly well suited for these studies given that it has two isotopes that can decay through 2νββ -- Xe-136 and Xe-134 -- and two that can decay through 2ν2EC and the mixed mode -- Xe-124 and Xe-126. This, together with its sheer size and extremely low background, places LZ in an excellent position for such studies.