The International Germanium Experiment (IGEX) has six HPGe detectors, isotopically enriched to 86% in ${}^{76}\mathrm{Ge},$ containing approximately 90 active moles of ${}^{76}\mathrm{Ge}.$ Three detectors of 2 kg each operate in the Canfranc Underground Laboratory (Spain) with pulse-shape analysis electronics. One detector (∼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 $T_{1/2}^{0\nu }>~0.8\times {10}^{25}\mathrm{yr}$ (90% C.L.), corresponding to $〈m_{\nu }〉<(0.5\mathrm{}–1.5)\mathrm{eV},$ depending on the theoretical nuclear matrix elements used to extract the neutrino mass parameter.

• Received 25 June 1998

DOI:https://doi.org/10.1103/PhysRevC.59.2108