Background Characterization of NEWS-G3 for Detecting Coherent Elastic Neutrino-Nucleus Scattering at a Nuclear Reactor

Abstract

The NEWS-G collaboration uses spherical proportional counters (SPCs) to perform a direct detection dark matter search for weakly interacting massive particles (WIMPs). SPCs exploit the ionization of gas to detect nuclear recoils at sub-keV sensitivities, which makes them excellent candidates for the detection of coherent elastic neutrino-nucleus scattering (CEvNS) using a nuclear reactor as a neutrino source. One of the greatest challenges in detecting CEvNS is overcoming the overwhelming backgrounds that obscure the elusive signals. NEWS-G3 is a new experiment using an SPC to detect CEvNS at a nuclear reactor. To suppress the background effects, NEWS-G3 has seven layers of passive shielding of varying materials and a single layer of an active muon veto scintillator system. The muon veto scintillator system has been successfully characterized and optimally calibrated and, through simulation, is shown to have an efficiency ≥99.85%. Simulation results explore the effects on overall muon-induced background rates for different veto window lengths and target gas parameters. First measurements using the NEWS-G3 detector result in a ≥98.5% background suppression, with future optimization to occur. The work presented in this thesis demonstrates an understanding of the expected background rates and highlights the feasibility of performing a CEvNS search using NEWS-G3 at a nuclear reactor.