# Suppression of alpha-induced lateral surface events in the COBRA experiment using CdZnTe detectors with an instrumented guard-ring electrode

## TL;DR

This paper demonstrates that instrumenting the guard-ring electrode in CdZnTe detectors significantly suppresses alpha-induced surface background events in the COBRA experiment, enhancing the detection sensitivity for neutrinoless double beta decay.

## Contribution

The study introduces a guard-ring electrode instrumentation method that achieves over 5300-fold suppression of alpha surface events, surpassing previous pulse-shape analysis techniques.

## Key findings

- Suppression factor of 5300 for alpha-induced events
- Retention of 85.3% of gamma events
- Superior suppression compared to pulse-shape analysis

## Abstract

The COBRA collaboration searches for neutrinoless double beta-decay ($0\nu\beta\beta$-decay) using CdZnTe semiconductor detectors with a coplanar-grid readout and a surrounding guard-ring structure. The operation of the COBRA demonstrator at the Gran Sasso underground laboratory (LNGS) indicates that alpha-induced lateral surface events are the dominant source of background events. By instrumenting the guard-ring electrode it is possible to suppress this type of background. In laboratory measurements this method achieved a suppression factor of alpha-induced lateral surface events of $5300^{+2660}_{-1380}$, while retaining $85.3\pm0.1\%$ of gamma events occurring in the entire detector volume. This suppression is superior to the pulse-shape analysis methods used so far in COBRA by three orders of magnitude.