Results on Neutrinoless Double-beta Decay of Ge-76 from Phase I of the GERDA Experiment

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 Ge-76. Data considered in the present analysis have been collected between November 2011 and May 2013 with a total exposure of 21.6 kg_s13_s178201_s19yr. A blind analysis is performed. The background index is about 1×10-2_s13_s178201_s19_s13_s178201_s19counts/(keV_s13_s178201_s19kg_s13_s178201_s19yr) after pulse shape discrimination. No signal is observed and a lower limit is derived for the half-life of neutrinoless double beta decay of Ge-76, T1/2(0_s13_s17957_s19)>2.1×10^25_s13_s178201_s19_s13_s178201_s19yr (90% C.L.). The combination with the results from the previous experiments with Ge-76 yields T1/2(0_s13_s17957_s19)>3.0×10^25_s13_s178201_s19_s13_s178201_s19yr (90% C.L.).