Search for neutrinoless double beta decay with the Gerda experiment: Phase II
Abstract
The GERmanium Detector Array (Gerda) experiment, located at the Gran Sasso underground laboratory in Italy, is built for the search of 0vββ decay in 76Ge. Gerda operates bare high purity germanium detectors submersed in liquid Argon (LAr). Phase I of the experiment was completed reaching an exposure of about 21 kg.yr with a background level of 10-2 cts/(keV.kg.yr). Gerda Phase I set a limit on the 0vββ decay of 76Ge of T1/20v > 2.1.1025 yr. In Phase II 35 kg of germanium detectors enriched in 76Ge are operated to reach an exposure of 100 kg.yr. The design goal is to reduce the background by one order of magnitude to reach the sensitivity for T1/20v = (1026) yr. The Phase II setup comprises thirty newly produced Broad Energy Germanium (BEGe) detectors. They contribute to the background reduction with better energy resolution and enhanced pulse shape discrimination. To achieve the necessary background reduction, the setup was complemented with LAr veto. The hardware upgrade for Phase II was finished and all detectors were deployed in December 2015. We present the first results of Phase II with 10.8 kg.yr exposure reached in June 2016.