Münster 2017 – scientific programme
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T: Fachverband Teilchenphysik
T 12: Neutrinophysik 2 (Doppelbetazerfall)
T 12.6: Talk
Monday, March 27, 2017, 18:05–18:20, VSH 118
Pulse Shape Discrimination for the Gerda Experiment — •Victoria Wagner for the GERDA collaboration — Max-Planck Institut für Kernphysik, Heidelberg
The Gerda experiment searches for neutrinoless double beta decay of 76Ge using high purity germanium (HPGe) detectors operated in liquid argon (LAr). The aim is to explore half-lives of the order of 1026 yr. Therefore, Gerda relies on improved active background reduction techniques such as pulse shape discrimination (PSD) in which the time structure of the germanium signals is analyzed to discriminate signal- from background-like events. Two types of HPGe detectors are operated: semi-coaxial detectors previously used in the Heidelberg-Moscow and IGEX experiments and new BEGe detectors. For semi-coaxial detectors a method based on an artificial neural network is used. Due to their special geometry, BEGe detectors feature an enhanced PSD. The analysis is based on a single parameter, the ratio of the maximum amplitude of the current pulse over the energy, A/E. 76 % of the background events in the region of interest are rejected while keeping a signal efficiency of 87 %. In Gerda Phase I, a background index of the order of 10−2 cts/keV·kg·yr has been achieved. The Phase II upgrade features an active veto based on the read-out of argon scintillation light (LAr veto) for further background discrimination. Together, PSD and LAr veto achieve a BI of the order of 10−3 cts/keV·kg·yr. With this unprecedented BI, less than one background event is expected until an exposure of 100 kg·yr. The talk reviews the applied PSD methods and their impact on the experimental sensitivity.