Understanding Pulse Shape Discrimination in Germanium Detectors: Diffusion Effects

The Gerda experiment is searching for neutrinoless double beta (0$\nu \beta \beta$) decay in ${}^{76}$Ge using high purity Germanium detectors. To reach sensitivities for the 0$\nu \beta \beta$ decay half-life of >10${}^{26}$ years the energy region of interest needs to be background free during the run time of the experiment. A crucial requirement to assure this is an excellent discrimination of signal and background like events. For this purpose pulse shape discrimination of the germanium detector signals is utilized. In the case of BEGe type detectors the ratio of the maximum amplitude of the current pulse and the energy, A/E, is used to distinguish between signal and background like events. In order to achieve a better understanding on how the A/E parameter depends on energy, simulations of the signal pulses have been performed. The simulations of charge carrier behavior make it possible to study the effects of charge diffusion, self-repulsion, and the initial charge cloud size on A/E. In this talk the implementation of the diffusion effects in the simulation will be summarized and their influence on the discrimination parameter will be discussed.