Pulse shape discrimination studies with a Broad-Energy Germanium detector for signal identification and background suppression in the GERDA double beta decay experiment

TL;DR

This study introduces a novel pulse shape discrimination method for Broad-Energy Germanium detectors, significantly improving background rejection in double beta decay experiments by efficiently identifying single-site events.

Contribution

The paper presents a new pulse shape analysis technique exploiting electrical field distribution in BEGe detectors for enhanced event discrimination.

Findings

Background survival probability for 60Co is 0.93%

Background suppression for 226Ra is 21%

Acceptance of double escape events is 89%

Abstract

First studies of event discrimination with a Broad-Energy Germanium (BEGe) detector are presented. A novel pulse shape method, exploiting the characteristic electrical field distribution inside BEGe detectors, allows to identify efficiently single-site events and to reject multi-site events. The first are typical for neutrinoless double beta decays (0-nu-2-beta) and the latter for backgrounds from gamma-ray interactions. The obtained survival probabilities of backgrounds at energies close to Q(76Ge) = 2039 keV are 0.93% for events from 60Co, 21% from 226Ra and 40% from 228Th. This background suppression is achieved with 89% acceptance of 228Th double escape events, which are dominated by single site interactions. Approximately equal acceptance is expected for 0-nu-2-beta-decay events. Collimated beam and Compton coincidence measurements demonstrate that the discrimination is largely independent of the interaction location inside the crystal and validate the pulse-shape cut in the energy range of Q(76Ge). The application of BEGe detectors in the GERDA and the Majorana double beta decay experiments is under study.