Robust Signal Extraction Methods and Monte Carlo Sensitivity Studies for the Sudbury Neutrino Observatory and SNO+ Experiments

The third and final phase of the Sudbury Neutrino Observatory (SNO) experiment utilized a series of He proportional counters called Neutral Current Detectors (NCDs) to detect the neutrons produced by the neutral current interactions of solar neutrinos in the detector. The number of neutrons detected by the NCDs, and hence the total flux of B solar neutrinos, has been determined using two novel signal extraction techniques which were designed to be robust against potential unexpected behaviour in the NCD background. These techniques yield total B solar neutrino flux measurements of 5.04 −0.40(stat)± 0.28(syst)x10cms and (4.40− 6.43)x10cms, which are in good agreement with previous SNO results and with solar model predictions, and which confirm that previous NCD analyses were not unduly affected by unexpected background behaviour. The majority of the hardware from the now-completed SNO experiment will be reused to create a new liquid scintillator based neutrino experiment called SNO+. An important part of the SNO+ physics program will be a search for neutrinoless double beta decay, carried out by dissolving Nd into the scintillator. The sensitivity of the SNO+ experiment to neutrinoless double beta decay has been evaluated. If loaded at 0.1% (w/w) with natural neodymium, after 1 kT·a of data taking SNO+ would have a 90%C.L. sensitivity of T 0ν 1/2 > 8.0x10 24 a or better 50% of the time; if the experiment were run with neodymium enriched to 50% in Nd this limit improves to 57x10 a. Under a reasonable choice for the Nd neutrinoless double beta decay matrix element, these half lives correspond to upper limits on the effective Majorana neutrino mass of 112 meV and 42 meV, respectively. These limits are competitive with those expected from all other near-term neutrinoless double beta decay experiments.