In-situ production of long-lived isotopes by cosmic muon interactions may generate a non-negligible background for deep underground rare event searches. Previous Monte Carlo studies for the GERDA experiment at LNGS identified the delayed decays of 77Ge and its metastable state 77mGe as dominant cosmogenic background in the search for neutrinoless double beta decay of 76Ge. This might limit the sensitivity of next generation experiments aiming for increased 76Ge mass at background-free conditions and thereby define a minimum depth requirement. A re-evaluation of the 77(m)Ge background for the GERDA experiment has been carried out by a set of Monte Carlo simulations. The obtained 77(m)Ge production rate is (0.21±0.01) nuclei/(kg⋅yr). After application of state-of-the-art active background suppression techniques and simple delayed coincidence cuts this corresponds to a background contribution of (2.7±0.3)⋅10−6 cts/(keV⋅kg⋅yr). The suppression achieved by this strategy equals an effective muon flux reduction of more than one order of magnitude. This virtual depth increase opens the way for next generation rare event searches.
@article{arxiv.1802.05040,
title = {Virtual depth by active background suppression: Revisiting the cosmic muon induced background of GERDA Phase II},
author = {C. Wiesinger and L. Pandola and S. Schönert},
journal= {arXiv preprint arXiv:1802.05040},
year = {2018}
}