UC Berkeley

This dissertation chronicles the role of optical photon-based detection technologies in the past, present, and future of neutrino physics. The initial chapters summarize the history of the field, following chapters explaining key areas of current research. The focus splits then splits, first covering studies with the current-generation, kiloton-scale SNO+ experiment, which has operated with significant amounts of liquid scintillator as its target since 2020. The next sections highlight work undertaken toward the development of a new paradigm known as “hybrid” detection, which aims to benefit from the two optical light emission mechanisms, Cherenkov radiation and scintillation, currently drawn on separately in today’s experiments.

For SNO+, the experiment is described and this work explores the first demonstrations of α and instrumental background rejection on scintillator data, performed using likelihood-ratio-based classification with hit timing. These demonstrations provide powerful tools for a broad range of physics analyses in SNO+. Additionally, an analysis to determine the 8B solar neutrino flux is performed on two datasets, one from when the SNO+ detector was only partially filled with liquid scintillator for an extended period of time due to the COVID-19 pandemic, and one from when the detector was completely full with the final scintillator cocktail for a period of over a year. The measured flux in both periods, [5.13+1.29−1.11(stat.)+0.45−0.53(syst.)]×10^6 cm^−2 s^−1 and [5.74+0.84−0.77(stat.)]×10^6 cm^−2 s^−1 respectively, is consistent with theoretical predictions from leading Standard Solar Models. This gives confidence in the understanding of SNO+’s operations in this period and adds to the family of measurements made of this flux around the community.

Subsequent discussion introduces the hybrid paradigm and outlines the areas where this technology is maturing. This dissertation presents key explorations into the physics potential at large-scales of this technology using well-motivated modeling and reconstruction for the first time. The potential for neutrinoless double beta decay and CNO solar neutrino flux measurements are examined, with capabilities akin to or exceeding state of the art experiments in a range of scenarios. Also presented is the particle identification capability of the novel scintillating medium water-based liquid scintillator based on lab-measured timing and light yield properties, with substantial rejection power identified between α and β signals. These explorations provide a confirmation of the possibilities for hybrid detection and help pave the way for concrete realizations of these technologies at larger scales.