The cosmic muon-induced background for the LEGEND-1000 alternative site at LNGS

The in-situ production of long-lived radio-isotopes by cosmic muon interactions may generate a non-negligible background for rare event searches in the deep subsurface. The delayed decay of ^77(m)Ge has been identified as the dominant in-situ cosmogenic contributor for a neutrinoless double-beta decay search with ⁷⁶Ge. The future ton-scale LEGEND-1000 experiment requires a total background of ≤ 10⁻⁵ cts/(keV·kg·yr). Dedicated Monte Carlo studies of the ^77(m)Ge background at the alternative LNGS site were performed. The addition of passive neutron moderators, in combination with a delayed coincidence strategy, results in a background contribution of 8.6×10⁻⁷ cts/(keV·kg·yr) with an additional dead time of < 9%.