Reactor Antineutrinos In The Sno+ Water Phase And Detector R&d For Large-Scale Neutrino Detectors

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Doctor of Philosophy (PhD)
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Physics & Astronomy
Elementary Particles and Fields and String Theory
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Kaptanoglu, Tanner

This dissertation presents two topics, both inspired by my work on the SNO+ experiment. First, I describe a search for reactor antineutrino interactions in the SNO+ water-filled detector using a 190.3 day dataset. Reactor neutrinos have never before been detected in a water Cherenkov detector, primarily due to the difficulty in detecting the low energy signal from neutron captures on free protons. However, enormous effort towards driving the trigger threshold to an unprecedentedly low level and reducing radioactive background levels have made this search possible in SNO+. The analysis described in this thesis uses a likelihood-ratio based approach to identify potential inverse beta decay interactions by selecting event pairs that are temporally and spatially coincident. This thesis presents the signal and background expectation and studies the background rates in carefully chosen sidebands. The signal window has has been partially unblinded, and a total of one event is observed, consistent with the expectation. Future efforts that build on the work presented in this thesis and include more SNO+ water-phase data are expected to result in the first ever significant detection of reactor antineutrinos in a water Cherenkov detector. The second topic in this thesis focuses on R&D effort relevant for current and future large-scale neutrino detectors, such as SNO+, KamLAND-Zen, JUNO, and THEIA. Detectors hoping to observe low-energy solar neutrinos and/or neutrinoless double beta decay will need high efficiency PMTs, state-of-the-art liquid scintillator, and new and emerging technology. My work in bench-top characterization of several modern PMTs and liquid scintillator mixtures has been critical for understanding the expected detector response and sensitivty of SNO+, future upgrades to SNO+, and other liquid scintillator detectors. Additionally, a new instrument called the dichroicon was developed to provide spectral photon sorting for large-scale Cherenkov and liquid scintillator detectors. The dichroicon is characterized on the bench-top and in simulation and shows excellent promise for use in future detectors.

Joshua Klein
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