The majorana 76Ge double-beta decay project

Abstract

The interest and relevance of next-generation 0 v ββ-decay experiments is increasing. Even with nonzero neutrino mass strongly suggested by solar and atmospheric neutrino experiments sensitive to δm 2, 0 v ββ-decay experiments are still the only way to establish the Dirac or Majorana nature of neutrinos by measuring the effective electron neutrino mass, 〈 m v 〉. 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 76Ge double-beta decay search. It will employ 500 kg of Ge, isotopically enriched to 86% in 76Ge, in the form of ∼ 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 68 Ge and 60 Co. The half-life sensitivity is estimated to be 4.2 × 10 27 y corresponding to a 〈 m v 〉 range of ≤ 20 − 70 meV, depending on the nuclear matrix elements used to interpret the data.