Wuppertal 2015 – scientific programme
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T: Fachverband Teilchenphysik
T 28: Niederenergie Neutrinophysik II
T 28.7: Talk
Monday, March 9, 2015, 18:15–18:30, I.12.01 (HS 30)
Investigation of n+ Surface Events in HPGe detectors for Liquid Argon Background Rejection in GERDA — •Bjoern Lehnert for the GERDA collaboration — TU-Dresden, Dresden
The GERDA experiment is searching for neutrinoless double beta decay (0νββ) in 76Ge using an array of germanium detectors immersed in liquid argon (LAr). Phase II of the experiment aims to improve the background level by a factor 10 in order to reach 10−3 counts / (kg·keV·yr). A strong suppression technique is required to suppress the intrinsic LAr background of 42Ar / 42K. 30 newly produced p-type Broad Energy Germanium (BEGe) detectors will be deployed in Phase II. The n+ electrode of the GERDA BEGe detectors is covering 96-98 % of the surface and is between 0.5 and 1.2 mm thick. Betas from the 42K decay can penetrated the detector surface and deposit energies within the 0νββ region. Experiences from GERDA Phase I show that these surface events are the dominate background component without suppression.
Energy depositions inside the n+ layer create pulse shapes that are slower than those from interactions in the bulk. This talk will present a rejection technique for those events. The signal development inside the n+ layer is modeled and applied in Geant4 Monte Carlo simulations. The simulations are compared with data for 241Am and 90Sr calibration source measurements. The suppression capabilities are extrapolated for 42K in GERDA Phase II.