The Majorana 76Ge double-beta decay project

The interest and relevance of next-generation 0(nu) betabeta-decay experiments is increasing. Even with nonzero neutrino mass strongly suggested by solar and atmospheric neutrino experiments sensitive to deltam(2), 0(nu) betabeta-decay experiments are still the only way to establish the Dirac or Majorana nature of neutrinos by measuring the effective electron neutrino mass, <m(nu)>. In addition, the atmospheric neutrino oscillation experiments imply that at least one neutrino has a mass greater than about 50 meV. The Majorana Experiment expects to probe an effective neutrino mass near this critical value. Majorana is a next-generation Ge-76 double-beta decay search. It will employ 500 kg of Ge, isotopically enriched to 86% in Ce-76, in the form of similar to 200 detectors in a close-packed array. Each crystal will be electronically segmented and each segment fitted with pulse-shape analysis electronics. This combination of segmentation and pulse-shape analysis significantly improves our ability to discriminate neutrinoless double beta-decay from internal cosmogenic Ge-68 and Co-60. The half-life sensitivity is estimated to be 4.2 x 10(27) y corresponding to a <m(nu)> range of less than or equal to 20-70 meV, depending on the nuclear matrix elements used to interpret the data.