Pulse shapes from electron and photon induced events in segmented high-purity germanium detectors

Abstract

Experiments built to search for neutrinoless double beta-decay are limited in their sensitivity not only by the exposure but also by the amount of background encountered. Radioactive isotopes in the surrounding of the detectors which emit gammaradiation are expected to be a significant source of background in the GERmanium Detector Array, GERDA.Methods to select electron induced events and discriminate against photon induced events inside a germanium detector are presented in this paper. The methods are based on the analysis of the time structure of the detector response. Data were taken with a segmented GERDA prototype detector. It is shown that the analysis of the time response of the detector can be used to distinguish multiply scattered photons from electrons.

Test of pulse shape analysis using single Compton scattering events

“…2.1. However, a conservative cut of R 90 < 2 mm is used to distinguish SSEs from MSEs [1]. The fractions of SSEs (f SSE ) in each sample are listed in Table 2.…”

“…The same artificial neural network (ANN) package as used in [1] is used here to perform the pulse shape analysis. The ANN is trained with an SSE sample against an MSE sample.…”

“…While the charge amplitude of the induced pulse is determined by the number of carriers (thus by the energy deposited), the time spectrum of the pulse (pulse shape) is determined by the location(s) of the energy deposition(s) and thus the charge drifting times. MSEs are expected to have more involved pulse shapes than SSEs, and thus, pulse shape analysis (PSA) can be used to separate the two classes of events [1][2][3][4][5][6].…”

“…Another common method to collect an SSE-dominant sample is to select the double-escape events (DEP) [1,3,4,6]. The incoming photon interacts with the germanium detector through pair production and the two 511 keV photons from the positron annihilation escape the detector without further interaction.…”

Background rejection and sensitivity for new generation Ge detectors experiments

“…A brief description of these simulations and algorithms and the results obtained are presented here, estimating the sensitivity that could be reached by a 0νβ β experiment using enriched germanium detectors and this technique. The performance of novel pulse shape analysis techniques has been also studied in other works [8,9,10,11].…”