PNNL

Abstract

P-type point contact (PPC) HPGe detectors are a leading technology for rare event searches in 36 germanium, due to their excellent energy resolution, low thresholds, and multi-site event rejection 37 capabilities. Alpha particles incident on the passivated surface of these detectors leads to a poorly 38 understood background. We have characterized a PPC detector's response to particles incident on the sensitive passivated and p+ 39 surfaces. The detector used is identical to those used in the Majorana Demonstratorexperiment, a search for 0 in 7640 Ge. Over most of the surface, we observe charge trapping and signicant energy loss in events. These events also exhibit a delayed charge signature caused by the slow recovery of a fraction of the trapped charge. This signature can be used to reliably identify background events on the passivated surface of the detector. In this measurement, this method is complementary to existing rising-edge-based analysis methods of identication. Combining the delayed charge recovery (DCR) discriminator with these methods, we 46 demonstrate the ability to effectively reject all surface events (to within statistical uncertainty7 with a loss of only 0.2% of bulk events. In the Majorana Demonstratorexperiment, this method has been used to reduce the background rate in the neutrinoless double-beta decay region of interest window by an order of magnitude; such a tool will likely be used in the upcoming LEGEND-200 experiment.