| Summary: | This thesis presents the first measurement of oscillation in antineutrinos from nuclear reactor cores, detected in liquid scintillator at SNO+. The small cluster of reactor cores along the Canadian-American border creates a distinct oscillated antineutrino energy spectrum, from which oscillation parameter values can be extracted. A likelihood analysis is presented, measuring the sensitivity to neutrino oscillation parameter ∆m 221 based on 100 tonne-years exposure. The Covid-19 pandemic forced a halt of the SNO+ scintillator fill, however stable data was recorded over 127 days in an approximately half-full detector. BiPo214 coincidence pairs provided an in-situ calibration of the LAB + 0.5g/L PPO scintillator cocktail. The reduced scintillator volume and livetime in the partially filled detector lead to limited sensitivity to the neutrino oscillation parameter ∆m^{2}_{21} . Strong agreement was seen between the 44 events measured in data and the total 45±6.7 stat events expected due to signal reactor antineutrinos and background geoneutrinos and α-n. Due to the limited statistics, two values of ∆m^{2}_{21} were favoured,8.8(+1.1,-1.3) and 12.6(+1.6,-1.3) ×10^{-5} eV^2. The current global PDG value of ∆m^{2}_{21} = 7.53±0.18×10^{-5}eV^{2} was found to be within a 1σ frequentist confidence interval of the smaller of the best-fit ∆m^{2}_{21} value. Following a successful first measurement of reactor antineutrinos, the analysis will be continued into the fully filled scintillator phases of SNO+. Simulation studies show that a precise measurement of ∆m 221 may be possible, where the current global uncertainty (dictated primarily by the KamLAND measurement) can be surpassed in 3-5 years of livetime in the Te-loaded scintillator phase, depending primarily on continued reactor activity and α-n levels. The uncertainty in ∆m^{2}_{21} impacts the interpretation of neutrino beam experimental results, making its measurement particularly relevant. Also discussed in this work, is a novel design for the next generation of large-scale liquid scintillator detectors (comparable to JUNO in size). The proposed ‘SLIPS’ design may allow for a much more simple and economical construction of large-scale liquid scintillator detectors, potentially impacting a number of areas, 0νββ and solar, supernova and geoneutrinos along with long baseline monitoring of reactors. Potential detector designs are discussed, with simulation studies demonstrating the possible quality of event reconstruction.
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