Photon identification in double beta decay-experiments using segmented germanium detectors

The sensitivity of experiments searching for neutrinoless double beta-decay of 76Ge is limited by background due to γ-radiation. The GERmanium Detector Array, GERDA, is a new experiment for which new background reduction techniques are developed. In the second phase of the experiment segmented detectors will be installed. The segmentation facilitates the identification of events with photons in the final state. The volume over which energy is deposited inside a detector depends on the incident particle. Photons with an energy around 1 MeV predominantly Compton-scatter and deposit energy on a cm-scale. In contrast, electrons with similar energies deposit energy locally on a mm-scale. For the segmentation scheme under study anti-coincidence requirements between the segments of a detector can be used to identify photons. In addition, the time structure of detector responses gives complementary information on the spread of energy inside the detector and thus allows further identification of photon events. Data was taken with a GERDA prototype detector and analyzed with respect to the potential of photon identification. The impact for GERDA is discussed. (orig.)