Final Results of GERDA on the Search for Neutrinoless Double-β Decay

The GERmanium Detector Array (GERDA) experiment searched for the lepton-number-violating neutrinoless double-beta (0 nu beta beta) decay of Ge-76, whose discovery would have far-reaching implications in cosmology and particle physics. By operating bare germanium diodes, enriched in Ge-76, in an active liquid argon shield, GERDA achieved an unprecedently low background index of 5.2 x 10(-4) counts/(keV kg yr) in the signal region and met the design goal to collect an exposure of 100 kg yr in a background-free regime. When combined with the result of Phase I, no signal is observed after 127.2 kg yr of total exposure. A limit on the half-life of 0 nu beta beta decay in Ge-76 is set at T-1/2 > 1.8 x 10(26) yr at 90% C.L., which coincides with the sensitivity assuming no signal.