The Energy Resolution of the SNO+ Detector in Liquid Scintillator Phase and Implications for Double Beta Sensitivity

Abstract

SNO+ is a multi-purpose liquid scintillator detector that ultimately aims to detect the hypothesized neutrinoless double beta decay (0νββ) through loading of 130Te as the target isotope. To this day the discovery of the neutrino mass and neutrino oscillations is the only proof of physics beyond the Standard Model. The detection of the rare 0νββ decay would revolutionize the field of physics and alter our understanding of the world. To perform such an experiment, the background rates must be extremely low in order to carry out the search for this signal in its energy region-of-interest. SNO+ is situated 2 km underground, in Creighton mine, Sudbury, ON. naturally shielded from cosmic radiation that otherwise would be extremely challenging to get rid of. One of the dominant systematic uncertainties in double beta decay analysis is expected to be the understanding of the energy resolution of the detector. In order to quantify whether the current understanding of the energy resolution is sufficient, a pure selection of mono-energetic 214Po events was collected utilizing 214Bi-214Po coincidences. A comparison of data and Monte Carlo simulation of the 214Po events yielded an estimate of the energy resolution systematic, which was then applied in sensitivity studies using fake datasets to evaluate its impact on the neutrinoless double beta decay sensitivity. Based on the best knowledge of the background in the detector in the liquid scintillator phase, this analysis developed a background model concerning the most contributing background sources in the region-of-interest for 0νββ decay to investigate the sensitivity levels of SNO+ at the current stage. These studies reveal that continued improvement in our understanding of the energy resolution is required.