NEXO light detection system

Abstract

nEXO is a future 5-tonne scale liquid xenon time projection chamber (TPC) experiment looking for hypothetical neutrinoless double beta decay of isotope 136Xe. To attain the projected half-life sensitivity of 1028 years, it aims to achieve an energy resolution of 1% or better at the Q-value (Qββ = 2.458 MeV) of the decay. nEXO plans to employ silicon photomultipliers (SiPMs) on the lateral surface of the cylindrical TPC to detect the light signals. Newly developed SiPMs sensitive to vacuum ultraviolet (VUV) light will be directly used for the detection of scintillation photons (λ = 175nm) in liquid xenon. For achieving the target energy resolution, the light detection system must have high photon detection efficiency, low correlated avalanche noise and low dark noise rate. The SiPM devices from two vendors are considered for the light detection system in the experiment. The primary goal of this research project is to characterize the VUV-SiPMs and measure their various features like gain, crosstalk, afterpulsing, dark noise rate, reflectivity and photon detection efficiency. Along with all these measurements, a monitoring tool will be required to test the large number of SiPMs before installing them in the detector. Current-voltage(IV) curve characterisation is being explored as a quick quality-testing tool for the performance of SiPM.