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Data Analysis of the Water and Scintillator Phases of SNO+ : from Solar Neutrino Measurements to Double Beta Decay Sensitivity Studies
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SNO+ is a leading liquid scintillator experiment for neutrino physics, with the ultimate goal of conducting a low background search for 0ѵꞵꞵ decay using 1300 kg of 130Te. The observation of this lepton-number-violating nuclear transition would provide fundamental insights regarding the neutrino mass and nature, opening doors to physics beyond the Standard Model. The success of this search relies on a complete understanding of the backgrounds contaminating the 0ѵꞵꞵ region-of-interest, and an accurate model of the energy response of the detector. Both are addressed continuously during three different stages of the experiment’s operations – water, scintillator and Te-loaded phases.
This thesis presents the analysis of data taken during the water and scintillator phases of the SNO+ experiment. Optical calibration data taken with a deployed source during the water phase allowed to measure for the first time in situ key optical parameters for the detector model, which will be common to all phases. The initial liquid scintillator data, taken during a 7 month transition period when the detector was half-filled with 365 tonnes of liquid scintillator on top of water, was used to characterize the intrinsic background contaminants in the scintillator. The background model was validated with a target-out double beta decay analysis, which tested for any unexpected background sources or leakage within the expected 0ѵꞵꞵ decay region-of-interest. Moreover, these data allowed the first physics measurement using scintillator in SNO+ – a measurement of the 8B solar neutrino flux, Փ8B =6.534 (+26.11%)/(-22.39%) (stat.) (+11.38%)/(-9.64%) (syst.) X 106 cm-2 s-1 with an exposure of 11.2 kt day, compatible with previous measurements by other experiments.
Based on the best knowledge of the backgrounds in the detector and of its energy response, a Monte Carlo based analysis was performed in order to evaluate the expected precision for the measurement of the 2ѵββ decay of 130Te, one of the major intrinsic background expected for the 0ѵββ search. Due to the large detector mass and isotope loading, SNO+ will achieve exposures competitive with other double beta decay experiments and statistical uncertainties well below 1% with a few months of data. It is expected that the future half-life measurement will be limited by systematic uncertainties due to energy scale and background correlations, which could be on the order of 5%. These will have to be accurately determined and minimized using calibrations after the tellurium is loaded.
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Decaimento beta duplo física de neutrinos calibração detector de Cherenkov detector de cintilador líquido Double beta decay neutrino physics calibration water Cherenkov detectors liquid scintillator Detectors