The CAGE Scanner: Development of a Novel Surface Event Rejection Technique in High Purity Germanium Detectors

Abstract

The search for neutrinoless double beta (0νββ) decay aims to answer far-reaching questions about thenature of the neutrino mass, violation of lepton number conservation in the Standard Model, and the matterantimatter asymmetry of the universe. The LEGEND experiment is pursuing this rare event search with the use of semiconductor detectors constructed of high-purity germanium, enriched in the candidate isotope 76Ge. Precise understanding of detector response to radiation is crucial to the success of this experimental effort. This work describes the operation and improvement of the Collimated Alphas, Gammas, and Electrons (CAGE) Scanner, a test cryostat dedicated to the study of surface event behavior in different germanium detector geometries. Analysis of CAGE scans led to the development of a new pulse shape parameter, Early Charge (EQ), which is then applied to a subset of LEGEND-200 data to investigate its impact on LEGEND-200 backgrounds.