Neutrino physics with the XENONnT experiment

One of the most active fields in physics is the search for Dark Matter, for which the XENON Project is one of the main protagonists. The new XENONnT experiment will be operative starting from 2020 in the underground Laboratori Nazionali del Gran Sasso, under 3600 meters water equivalent of mountain rock shield. It is a multi-ton detector for direct search of Dark Matter, consisting of a double phase liquid-gas xenon TPC which contains 5.9 t of liquid xenon target mass, inserted in a Cryostat surrounded by a tank containing 700 t of Gd-loaded water, instrumented with PMTs for muon and neutron tagging. Its aim, as that of its precursor XENON1T, is to detect WIMPs elastic scattering off xenon nucleus through the measure of the light and charge observable signals produced by recoils in LXe. A new neutron Veto system, surrounding the outer Cryostat and instrumented with 120 additional PMTs, will contribute to reduce the neutron background in the TPC. Thanks to the large xenon target used, this experiment is sensitive also to all flavors of Supernova neutrinos. These can be detected through two different interactions channels: through coherent elastic scatters on xenon nuclei in the TPC and through interactions of electron antineutrinos with protons of water via inverse beta decay process. In the first part of this work, after a theoretical introduction to neutrino physics, I present the results of a Monte Carlo simulation to predict the XENONnT detection efficiencies for neutrino events as IBD interactions in the neutron and muon Vetoes. In the last part of the thesis, I investigate the XENONnT possibility to detect neutrinoless double beta decay of Xe-136 isotope, a Standard Model forbidden decay which can prove the Majorana nature of neutrinos. Starting from evaluation of the ER background rate from Cryostat and PMTs in the energy region where we expect to observe neutrinoless double beta decay, the sensitivity of XENONnT for this nuclear decay was estimated.