Neutrino physics with the XENONnT Water Cherenkov Veto

Dark Matter and neutrinos constitute two of the most elusive components of the Universe. The XENONnT experiment, located at the underground INFN Laboratori Nazionali del Gran Sasso (LNGS) in Italy, aims to detect Weakly Interacting Massive Particles (WIMPs), one of the leading Dark Matter candidates nowadays. A dual-phase Time Projection Chamber (TPC) filled with 6 t of liquid xenon is employed to achieve this purpose. The TPC is surrounded by the Neutron Veto (NV) and the Muon Veto (MV), which operate in coincidence with the core detector to discriminate backgrounds such as radiogenic neutrons and cosmic muons. The Muon Veto contains approximately 700 tonnes of water, with about 34 tonnes being nearly optically separated in the inner Neutron Veto. Neutrinos, through coherent neutrino-nucleus scattering (CE$\upnu$NS), constitute a major background due to their similarity to a WIMP signal. Nevertheless, neutrinos are also an important signal to be investigated. Therefore, assessing the NV and MV ability to detect signals from two of the most important neutrino sources in the MeV-GeV range, galactic core-collapse supernova (CCSN) and atmospheric neutrinos, is crucial. Simulations of a benchmark CCSN scenario in the MV (NV) predict 108 (8) detected positron events, out of the expected 162 (8) inverse beta decay interactions occurring within a 10 s burst. This study concludes that the NV features a positron detection threshold of about 0.5 MeV, while the MV exhibits a $\sim$5 MeV detection threshold. Atmospheric neutrino interactions yield an annual rate of 56 (4) detected out of approximately 88 (5) expected events in the MV (NV), arising from interactions in pure water of electron and muon neutrinos and antineutrinos. Extrapolating these results to XLZD by assuming a proposed MV+NV configuration with $\sim1300$ tonnes of total water volume and the same performance of the XENONnT vetoes, the detection of 118 atmospheric neutrino events per year can be achieved.