Calibration of the Scintillation Timing in SNO+ using In-Situ Backgrounds

Abstract

The SNO+ Collaboration has recently concluded loading its liquid scintillator with PPO, the primary fluor, and the loading of the wavelength shifter, bisMSB, is ongoing. For each stage of the experiment, reliable position and energy reconstruction is essential, and in the face of a changing scintillator cocktail, methods have been developed to rapidly calibrate the SNO+ optical model. To this end, a novel technique for calibrating the time response of the SNO+ liquid scintillator using in-situ backgrounds was developed. By using in-situ coincident backgrounds, it is possible to calibrate both the $\beta^-$ and $\alpha$ time responses, as well as facilitate frequent monitoring of the background levels without compromising the radiopurity of the detector. Accurate calibration of the liquid scintillator emission times allows the exploration of time-based particle discrimination, such as between single-site ($\beta^-$) and multi-site ($\beta^- \gamma$) interactions.