Pulse fitting for event localization in high purity germanium point contact detectors

Abstract

P-type Point Contact (PPC) detectors are used in rare-event searches, such as neutrinoless double-beta decay and dark matter searches, due to their low radioactive backgrounds and low energy thresholds. The Majorana collaboration operates the Majorana Demonstrator experiment, which uses high purity germanium (HPGe) point contact (PPC) detectors with the goal of experimentally observing neutrinoless double-beta decay. Neutrinoless double-beta decay is an experimental proof of the hypothesis that neutrinos are Majorana particles. Observing this decay can give us major insights into physics beyond the Standard Model of particle physics. But to observe neutrinoless double-beta decay, experiments have to be designed to detect the faintest signals because the current best lower limit of the half-life of the decay is ~ 10^25 years. This work aims to determine the location of the energy depositions in PPC detectors using the charge signal that is collected from the single point contact electrode. By comparing the charge signals to a library of simulated signals, events can be localized, in some cases, with a resolution of 1mm. This is of interest in localizing low energy backgrounds in these types of detectors.