Background Suppression Using Pulse Shape Analysis with a BEGe Detector for Neutrinoless Double Beta Decay Search with GERDA

A pulse shape analysis for distinguishing between double beta decay-like interactions and multiple-scattered photons was performed for the first time using a BEGe-type detector. This discrimination method is included in the research and development for the second phase of the GERDA experiment, since active background suppression techniques are necessary to reach sensitivity for the ⁷⁶Ge neutrinoless double beta decay half life of >10²⁶ years. A suppression of backgrounds in the energy region of interest around the ⁷⁶Ge Q_ββ = 2039 keV is demonstrated, with (0.93±0.08)% survival probability for events from ⁶⁰Co, (21±3)% for ²²⁶Ra, and (40±2)% for ²²⁸Th. This performance is achieved with (89±1)% acceptance of ²²⁸Th double escape events, which are analogous to double beta decay.