Pulse Shape Discrimination of Bulk and Very Bulk Events within HPGe Detectors

TL;DR

This paper presents two pulse shape discrimination methods, CCM and Fisher's LDA, to distinguish bulk from very bulk events in HPGe detectors, improving background rejection for dark matter searches.

Contribution

It introduces and compares two linear PSD techniques, CCM and Fisher's LDA, for effective discrimination of event types in HPGe detectors.

Findings

FOM for CCM is 1.38 ± 0.33

FOM for Fisher's LDA is 1.62 ± 0.18

Both methods effectively discriminate event types

Abstract

The CDEX (China Dark matter Experiment) now deploys ~10 kg pPCGe (p-type Point Contact Germanium) detectors in CJPL (China Jinping Underground Laboratory). It aims to detect rare events such as dark matter and 0vbb (neutrinoless double beta decay). The discrimination of bulk and very bulk events are essential for improvements of the analysis threshold of dark matter. Very bulk events are generated near the p+ point surface of pPCGe, which are usually from radioactive materials of electronic devices. Due to different locations of charge collection, bulk and very bulk events have different pulse shape. This paper will present two linear PSD (Pulse Shape Discrimination) methods: CCM (Charge Comparison Method) and Fisher's LDA (Linear Discriminant Analysis), to realize the discrimination of bulk and very bulk events. The results show that FOMs (Figure of Merit) are 1.38 $\pm$ 0.33 and 1.62 $\pm$ 0.18 by CCM and Fisher's LDA respectively.