Search for the in-situ production of 77Ge in the GERDA neutrinoless double-beta decay experiment

The beta decay of Ge and Ge, both produced by neutron capture on Ge, is a potential background for Germanium based neutrinoless double-beta decay search experiments such as GERDA or the LEGEND experiment. In this work we present a search for Ge decays in the full GERDA Phase II data set. A delayed coincidence method was employed to identify the decay of Ge via the isomeric state of As (, , μ , As). New digital signal processing methods were employed to select and analyze pile-up signals. No signal was observed, and an upper limit on the production rate of Ge was set at nuc/(kg yr) (90% CL). This corresponds to a total production rate of Ge and Ge of nuc/(kg yr) (90% CL), assuming equal production rates. A previous Monte Carlo study predicted a value for in-situ Ge and Ge production of (0.21 ± 0.07) nuc/(kg.yr), a prediction that is now further corroborated by our experimental limit. Moreover, tagging the isomeric state of As can be utilised to further suppress the Ge background. Considering the similar experimental configurations of LEGEND-1000 and GERDA, the cosmogenic background in LEGEND-1000 at LNGS is estimated to remain at a sub-dominant level.