Results on neutrinoless double beta decay of⁷⁶Ge from the GERDA experiment

Abstract

Abstract. The Germanium Detector Array (GERDA) experiment is searching for neutrinoless double beta (0νββ) decay of 76 Ge, a lepton number violating nuclear process predicted by extensions of the Standard Model. GERDA is an array of bare germanium diodes immersed in liquid argon located at the Gran Sasso National Laboratory (LNGS) in Italy. The results of the GERDA Phase I data taking with a total exposure of 21.6 kg yr and a background index of 0.01 cts/(keV kg yr) are presented in this paper. No signal was observed and a lower limit of T 0ν 1/2 > 2.1 × 10 25 yr (90% C.L.) was derived for the half-life of the 0νββ decay of 76 Ge. Phase II of the experiment aims to reduce the background around the region of interest by a factor of ten.