Pulse Shape Discrimination In Cupid-Mo Using Principal Component Analysis

CUPID-Mo is a cryogenic detector array designed to search for neutrinoless double-beta decay (0 nu beta beta) of Mo-100. It uses 20 scintillating Mo-100-enriched Li2MoO4 bolometers instrumented with Ge light detectors to perform active suppression of alpha backgrounds, drastically reducing the expected background in the 0 nu beta beta 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.