Thesis

Study of neutrino interactions and search for rare decay events in the LZ dark matter search experiment

• Call:

  IDPASC Portugal - PHD Programme 2016

• Academic Year:

  2016 / 2017

• Domains:

  Astrophysics | Astroparticle Physics

• Supervisor:

  Alexandre Lindote

• Co-Supervisor:

  Francisco Neves

• Institution:

  Universidade de Coimbra

• Host Institution:

  Laboratório de Instrumentação e Física Experimental de Partículas

• Abstract:

  Merging two teams with wide experience and an history of leadership in the field of direct dark matter detection (LUX and ZEPLIN), the LZ collaboration is developing a 10-ton dual-phase Liquid Xenon detector, 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 this detector to improve the current best sensitivity to WIMPs (the leading dark matter candidate) 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. While being an irreducible source of background in the context of WIMP search, the high sensitivity of LZ will allow it to make real time observations of solar pp fusion neutrinos via elastic ve->ve scattering. LZ will also be sensitive to neutrino coherent nuclear scattering, a process that has never been observed. Understanding the expected neutrino interactions and the detector response they create is paramount for the WIMP search effort, but will simultaneously allow to study fundamental neutrino properties and their astrophysics sources (e.g. survival probability, solar neutrino flux, sterile neutrino mixing angle). Rare decays in xenon also constitute a background for WIMP search, making it crucial to understand their expected rates and the detector response, but are interesting in their own right. Some of these decay modes may be observed for the first time in LZ, while for others the current lifetime limits can be improved. While several experiments study the double beta (2ß) decay of Xe-136, that of Xe-134 may be first seen in LZ. Of even higher interest are the double beta plus (2ß+), double electron capture (2EC) and the mixed mode expected for Xe-124. Two neutrinos double electron capture (2v2EC) is a decay mode allowed by the Standard Model, in which two of the orbital electrons are captured by two protons and two neutrinos are emitted. It is only possible in 35 isotopes and its detection is challenging -- given the long half-life (O(10^21 years)) and the fact that only X-rays and Auger electrons from the excited final atom can be detected. The extra decay modes, with positron emission, are also possible but less favored by kinematics; a search for those decay modes -- further complicated by their continuous energy spectra -- is also foreseen.