Pulse Shape Discrimination in CUPID-Mo using Principal Component Analysis

Abstract

CUPID-Mo is a cryogenic detector array designed to search for neutrinoless double-beta decay ($0\hat{I}½{\hat{I}}^2{\hat{I}}^2$) of ${}^{100}$Mo. It uses 20 scintillating ${}^{100}$Mo-enriched Li${}_2$MoO${}_4$ bolometers instrumented with Ge light detectors to perform active suppression of $\hat{I}\pm$ backgrounds, drastically reducing the expected background in the $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ signal region. As a result, pileup events and small detector instabilities that mimic normal signals become non-negligible potential backgrounds. These types of events can in principle be eliminated based on their signal shapes, which are different from those of regular bolometric pulses. We show that a purely data-driven principal component analysis based approach is able to filter out these anomalous events, without the aid of detector response simulations.