Characterizations of Future Low-Energy Neutrino Experiments at the Spallation Neutron Source

Abstract

Measurements of low-energy neutrino-nucleus interactions provide a sensitive probe of physics beyond the Standard Model. One such interaction, coherent elastic neutrino-nucleus scattering (CEvNS), was first observed in 2017 and has since become the focus of an expanding experimental program. The development of next-generation CEvNS detectors requires detailed characterization of detector materials at low energies.This work investigates cryogenic undoped cesium iodide as a potential target material for CEvNS detection. To enable its application, measurements of the nuclear recoil response, or quenching factors, are required. This thesis reports the first measurement of quenching factors in undoped cesium iodide cooled to 77 K, establishing values in the range 12.8–18.8% for nuclear recoil energies between 8 and 52 keVnr.The implications of CEvNS measurements for sterile neutrino phenomenology are also considered. Constraints on sterile neutrino mixing parameters are derived from existing COHERENT data, and sensitivity projections are developed for future detectors. These include the first projections that combine neutral-current and charged-current detection channels.The results presented here inform the characterization of cesium iodide as a CEvNS detector medium and the role of COHERENT data in constraining sterile neutrino models.