Data Acquisition and Analysis of the 76Ge Double Beta Experiment in Gran   Sasso 1990-2003
  Data acquisition in a long running underground experiment has its specific experimental challenges, concerning data acquisition, stability of the experiment and background reduction. These problems are addressed here for the HEIDELBERG-MOSCOW experiment, which collected data in the period August 1990 - May 2003. The measurement and the analysis of the data is presented. The duty cycle of the experiment was ~80%, the collected statistics is 71.7 kgy. 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 a 4 sigma level. 
H.V. Klapdor-Kleingrothaus, A. Dietz, I.V. Krivosheina and O.   Chkvorets