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 are presented. The duty cycle of the experiment was ~80%, and the collected statistics is 71.7 kg year. The background achieved in the energy region of the Q value for double beta decay is 0.11 events/kg year 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 level