Post-upgrade performance of GERDA Phase II

Abstract

Excellent spectroscopic performance, event topology information and outstanding radiopurity are unique properties of HPGe detectors that facilitate the search for 0vββ decay of 76Ge. A detection of this process would shed light onto physics beyond the standard model, as it would uncover the Majorana nature of neutrinos. The GERDA experiment employs an array of HPGe detectors, made from isotopically modified material, in an active liquid argon shield at the LNGS underground laboratory. The combination of an ultra-low background environment with active background rejection techniques allows the exploration of 0vββ decay half-lives beyond 1026 yr. No signal has been found in the first 58.9 kg⋅yr of Phase II data, from which the most stringent limit on 0vββ decay of 76Ge has been derived. In the course of an upgrade new HPGe detectors of novel type have been added to the array, increasing the total mass of enriched germanium to 44.2 kg. More than one year of data has been collected in this configuration. The first 24.9 kg⋅yr reveal encouraging performance for the ongoing 0vββ decay search.