Search for neutrinoless double beta decay with enriched 76Ge in Gran   Sasso 1990-2003
  The results of the HEIDELBERG-MOSCOW experiment which searches with 11 kg of enriched 76Ge for double beta decay in the GRAN Sasso underground laboratory are presented for the full running period August 1990 - May 2003. The duty cycle of the experiment was ~80%, the collected statistics is 71.7 kg y. The background achieved in the energy region of the Q value for double beta decay is 0.11 events/ kg y keV. The two-neutrino accompanied half-life is determined on the basis of more than 100 000 events. The confidence level for the neutrinoless signal has been improved to 4.2 sigma. 
H.V. Klapdor-Kleingrothaus, I.V. Krivosheina, A. Dietz, and O.   Chkvorets (MPI-Kernphysik, Heidelberg, Germany)