THE EVIDENCE FOR THE OBSERVATION OF 0νββ DECAY: THE IDENTIFICATION OF 0νββ EVENTS FROM THE FULL SPECTRA

In this brief review, a description of the observed evidence for neutrinoless double beta 3–5 in the 76 Ge experiment in Gran Sasso (Heidelberg–Moscow experiment) which has been operated with 11 kg enriched 76 Ge detectors in the period 1990–2003, is provided. Two different methods of pulse shape analysis have been used to select potential 0νββ events from the γ background of the measured spectrum — a selection by a neuronal net approach, 3,4,16 and a selection by a new method comparing measured pulses with a library of pulse shapes of point-like events calculated from simulation of the electric field distribution in the detectors (see Refs. 6–8 and 37). The latter method also allows spatial localization of measured events. Both methods lead to selections of events at Q ββ with almost no γ-background. The observed line at Q ββ is identified as a 0νββ signal. It has a confidence level of more than 6σ.