Neutrinoless double-β decay of 76Ge:: First results from the International Germanium Experiment (IGEX) with six isotopically enriched detectors

The International Germanium Experiment (IGEX) has six HPGe detectors, isotopically enriched to 86% in Ge-76, containing approximately 90 active moles of Ge-76, These detectors of 2 kg each operate in the Canfranc Underground Laboratory (Spain) with pulse-shape analysis electronics, One detector (similar to 0.7 kg active volume) has been operating in the Baksan Low-Background Laboratory for several years. and two additional similar detectors will operate in Baksan. A maximum likelihood analysis of 74.84 active mole years of data yields a lower bound T(1/2)(0v)greater than or equal to 0.8 x 10(25) yr (90% C.L.), corresponding to [M-v] <(0.5-1.5) eV, depending on the theoretical nuclear matrix elements used to extract the neutrino mass parameter. [S0556-2813(99)01604-0].