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neutrinoSNO+ Report Summary

Project ID: 278310
Funded under: FP7-IDEAS-ERC
Country: United Kingdom

Final Report Summary - NEUTRINOSNO+ (Probing fundamental properties of the neutrino at the SNO+ Experiment)

This project has significantly advanced the analysis tools of the SNO+ collaboration in readiness for data analysis across all the planned data taking phases. Although the SNO+ project has suffered significant delays beyond the control of this project, meaning that we have only recently commenced stable data taking in the first, water-filled, phase of detector operation, the analysis tools are in an advanced stage of readiness to be applied as data becomes available.
We have commissioned the in-situ optical modules, designed to measure the Rayleigh scattering in the detector with collimated beams of laser light, using initial data taken with the partially filled detector such that we are confident that we can accurately simulate the expected beam pulses. The analysis tools to extract the Rayleigh scattering in both the water and scintillator filled detector have been developed and thoroughly tested on Monte Carlo data sets and are ready for application as soon as the full detector calibration runs are taken. We expect to be able to measure the wavelength-dependent scattering length in the water to an accuracy of ~25%, and have shown that the remaining uncertainty will have negligible effects on the measured timing, charge and hit distributions of events within the detector.
We have developed a technique to securely contain a pure Yttrium-90 beta-emitting calibration source in glass micro-capillaries with negligible attenuation of the beta radiation, allowing calibration of liquid scintillator light yield directly for beta radiation. Safe practises were developed for preparing and handling the source, but the risk of contamination to the SNO+ detector could not be completely mitigated so we chose to focus on using this source in separate test stands for studying the scintillator properties. However, we identified the potential to use in-situ radioactive background sources (C14, Bi210, Po210 and BiPo214) to calibrate the energy resolution of the SNO+ detector in response to beta and alpha radiation and have developed analysis tools to fit the energy resolution with a predicted accuracy of **% without any risk of detector contamination.
We have prepared detailed analysis tools in readiness for measuring low energy solar neutrino fluxes and searching for neutrinoless double beta decay signals. The most challenging aspect of both these analyses is to be able to characterise and reject background events from other sources such as radioactive contamination in the detector media, and to accurately account for the effects of uncertainties in the detector response on the final physics measurements. We have advanced the collaboration’s tools for fitting out the signal and background components from measured energy spectra, including the addition of new features to account for the particle dependent variations in response that we have identified, and methodology to optimise the information obtained from separate background sources to constrain systematic uncertainties.
Detailed studies of many background components including random event pile-up and 214BiPo and 212BiPo fast coincidence events have been conducted and tools have been developed to tag and reject these background contributions such that they are reduced by many orders of magnitude and make only small contributions to the total background count for both the solar and double beta analyses. The effect of different scintillator optical properties on these algorithms has been studied. The amount of signal sacrificed by applying the developed rejection criteria is also now well understood, such that we can effectively optimise and apply the SNO+ analyses once data is available.
In order to perform the above analyses, we have invested significant time and expertise into developing the SNO+ Monte Carlo and Data Processing software, including the addition of critical reconstruction algorithms and utilities to support Grid computing resources. With this legacy, the SNO+ collaboration is now smoothly processing data as it arrives from the detector ready for speedy analysis, and has capabilities to prepare large accurate Monte Carlo Simulations of the SNO+ detector.

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United Kingdom
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