The Heidelberg-Moscow double beta decay experiment with enriched 76Ge: First results

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Abstract Status and perspectives of the HEIDELBERG-MOSCOW double beta decay experiment which is undertaken in the GRAN SASSO laboratory, are presented. Of the 16.9 kg of enriched (86%) 76Ge in hands of the cooperation, 6.5 kg have been converted into detectors. A 1 kg enriched detector was installed in July 1990, a 2.9 kg enriched detector, the largest HP Ge detector ever produced, with efficiency of 118% has been installed by september 1991. Present limits for 0νββ decay to the g.s. and first excited state of 76Se, respectively, are: T 1 2 0ν (0 + → 0 + ) > 1.1 (2.0) × 10 24 y, and T 1 2 0ν (0 + → 0 + ) > 2.2 (3.6) × 10 23 y with 90% (68%) c.1. These values are the most stringent directly measured 0νββ half life limits known up to now. They correspond to an effective neutrino mass limit of