Results on neutrinoless double beta decay of 76Ge from GERDA Phase I

TL;DR

This paper reports the results of the GERDA Phase I experiment searching for neutrinoless double beta decay in 76Ge, setting new lower limits on the decay half-life and improving constraints on lepton number violation.

Contribution

First comprehensive results from GERDA Phase I with improved background suppression and combined analysis establishing more stringent half-life limits for neutrinoless double beta decay in 76Ge.

Findings

No signal observed for neutrinoless double beta decay.

Lower limit on half-life: > 2.1 x 10^{25} years (90% C.L.).

Combined data yields half-life > 3.0 x 10^{25} years (90% C.L.).

Abstract

Neutrinoless double beta decay is a process that violates lepton number conservation. It is predicted to occur in extensions of the Standard Model of particle physics. This Letter reports the results from Phase I of the GERmanium Detector Array (GERDA) experiment at the Gran Sasso Laboratory (Italy) searching for neutrinoless double beta decay of the isotope 76Ge. Data considered in the present analysis have been collected between November 2011 and May 2013 with a total exposure of 21.6 kgyr. A blind analysis is performed. The background index is about 1.10^{-2} cts/(keV kg yr) after pulse shape discrimination. No signal is observed and a lower limit is derived for the half-life of neutrinoless double beta decay of 76Ge, T_1/2 > 2.1 10^{25} yr (90% C.L.). The combination with the results from the previous experiments with 76Ge yields T_1/2 > 3.0 10^{25} yr (90% C.L.).