Eur. Phys. J. C (2022) 82: 226
https://doi.org/10.1140/epjc/s10052-022-10161-y

Special Article - Tools for Experiment and Theory

-event characterization and rejection in point-contact HPGe detectors

¹ Pacific Northwest National Laboratory, 99354, Richland, WA, USA
² Department of Physics and Astronomy, University of South Carolina, 29208, Columbia, SC, USA
³ Oak Ridge National Laboratory, 37830, Oak Ridge, TN, USA
⁴ National Research Center “Kurchatov Institute” Institute for Theoretical and Experimental Physics, 117218, Moscow, Russia
⁵ Department of Physics, University of South Dakota, 57069, Vermillion, SD, USA
⁶ Department of Physics, North Carolina State University, 27695, Raleigh, NC, USA
⁷ Triangle Universities Nuclear Laboratory, 27708, Durham, NC, USA
⁸ Max-Planck-Institut für Physik, 80805, Munich, Germany
⁹ Physik-Department, Technische Universität, 85748, Munich, Germany
¹⁰ South Dakota School of Mines and Technology, 57701, Rapid City, SD, USA
¹¹ Department of Physics and Astronomy, University of North Carolina, 27514, Chapel Hill, NC, USA
¹² Department of Physics, Duke University, 27708, Durham, NC, USA
¹³ Center for Experimental Nuclear Physics and Astrophysics, and Department of Physics, University of Washington, 98195, Seattle, WA, USA
¹⁴ Nuclear Science Division, Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA
¹⁵ Los Alamos National Laboratory, 87545, Los Alamos, NM, USA
¹⁶ Department of Physics and Astronomy, University of Tennessee, 37916, Knoxville, TN, USA
¹⁷ Physics Department, Williams College, 01267, Williamstown, MA, USA
¹⁸ Department of Physics, Engineering Physics and Astronomy, Queen’s University, K7L 3N6, Kingston, ON, Canada
¹⁹ Department of Physics, Indiana University, 47405, Bloomington, IN, USA
²⁰ IU Center for Exploration of Energy and Matter, 47408, Bloomington, IN, USA
²¹ Joint Institute for Nuclear Research, 141980, Dubna, Russia
²² SLAC National Accelerator Laboratory, 94025, Menlo Park, CA, USA
²³ Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, 28040, CIEMAT, Madrid, Spain
²⁴ Applied Physics Laboratory, Johns Hopkins University, 20723, Laurel, MD, USA
²⁵ Applied Research Associated, 27615, Raleigh, NC, USA
²⁶ Jet Propulsion Laboratory, California Institute of Technology, 91109, Pasadena, CA, USA
²⁷ Universität Hamburg, 20146, Hamburg, Germany

^ac jgruszko@unc.edu

Received: 25 February 2021
Accepted: 23 February 2022
Published online: 15 March 2022

Abstract

P-type point contact (PPC) HPGe detectors are a leading technology for rare event searches due to their excellent energy resolution, low thresholds, and multi-site event rejection capabilities. We have characterized a PPC detector’s response to particles incident on the sensitive passivated and p surfaces, a previously poorly-understood source of background. The detector studied is identical to those in the MajoranaDemonstrator experiment, a search for neutrinoless double-beta decay () in Ge. decays on most of the passivated surface exhibit significant energy loss due to charge trapping, with waveforms exhibiting a delayed charge recovery (DCR) signature caused by the slow collection of a fraction of the trapped charge. The DCR is found to be complementary to existing methods of identification, reliably identifying background events on the passivated surface of the detector. We demonstrate effective rejection of all surface events (to within statistical uncertainty) with a loss of only 0.2% of bulk events by combining the DCR discriminator with previously-used methods. The DCR discriminator has been used to reduce the background rate in the region of interest window by an order of magnitude in the MajoranaDemonstrator  and will be used in the upcoming LEGEND-200 experiment.