Theoretical investigation of the dependence of double beta decay tracks in a Ge detector on particle and nuclear physics parameters and separation from gamma ray events

The sizes of tracks of events of neutrinoless double-beta decay in a Germanium detector depend on particle physics and nuclear physics parameters such as neutrino mass, right-handed current parameters, etc., and nuclear matrix elements. In this paper for the first time Monte Carlo simulations of neutrino-accompanied (2νββ) and neutrinoless double-beta decay (0νββ) events, and of various kinds of background processes such as multiple and other γ interactions are reported for a Ge detector. The time history of the evolution of the individual events is followed and the sizes of the events (partial volumes in the detector inside which the energy of the event is released) are investigated. Effects of the angular correlations of the two electrons in ββ decay, which again depend on the above nuclear and (for 0νββ decay) on particle physics parameters, are taken into account and have been calculated for this purpose for the first time on basis of the experimental half-life of 76Ge and of realistic nuclear matrix elements. The sizes determine, together with the location of the events in the detector, the pulse shapes to be observed. It is shown for ββ decay of 76Ge, that ββ events should be selectable with high efficiency by rejecting large size (high multiplicity) γ events. Double-escape peaks of similar energy of γ lines show concerning their sizes similar behavior as 0νββ events, and in that sense can be of some use for corresponding 'calibration' of pulse shapes of the detector. The possibility to distinguish ββ events from γ events is found to be essentially independent of the particle physics parameters of the 0νββ process. A brief outlook is given on the potential of future experiments with respect to determination of the particle physics parameters ,<λ>,<η>