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

## TL;DR

This paper reports a search for the in-situ production of 77Ge in the GERDA experiment, which is important for reducing background noise in neutrinoless double-beta decay studies.

## Contribution

The study introduces new digital signal processing methods and sets an upper limit on 77Ge production rates.

## Key findings

- No signal of 77Ge decay was observed in the GERDA Phase II dataset.
- An upper limit of <0.216 nuc/(kg·yr) was set for the production rate of 77Ge at 90% confidence level.
- The isomeric state of 77mAs can be used to suppress 77Ge background in future experiments.

## Abstract

The beta decay of \documentclass[12pt]{minimal}
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\begin{document}$$^{77}$$\end{document}77Ge and \documentclass[12pt]{minimal}
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\begin{document}$$^{77\textrm{m}}$$\end{document}77mGe, both produced by neutron capture on \documentclass[12pt]{minimal}
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\begin{document}$$^{76}$$\end{document}76Ge, 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 \documentclass[12pt]{minimal}
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\begin{document}$$^{77}$$\end{document}77Ge decays in the full GERDA Phase II data set. A delayed coincidence method was employed to identify the decay of \documentclass[12pt]{minimal}
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\begin{document}$$^{77}$$\end{document}77Ge via the isomeric state of \documentclass[12pt]{minimal}
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\begin{document}$$^{77}$$\end{document}77As (\documentclass[12pt]{minimal}
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\begin{document}$$9/2^+$$\end{document}9/2+, \documentclass[12pt]{minimal}
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\begin{document}$${475}\,\hbox {keV}$$\end{document}475keV, \documentclass[12pt]{minimal}
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\begin{document}$${T_{1/2} = {114}\,{\upmu }\hbox {s}}$$\end{document}T1/2=114μs, \documentclass[12pt]{minimal}
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\begin{document}$$^{77\textrm{m}}$$\end{document}77mAs). 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 \documentclass[12pt]{minimal}
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\begin{document}$$^{77}$$\end{document}77Ge was set at \documentclass[12pt]{minimal}
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\begin{document}$$<0.216$$\end{document}<0.216 nuc/(kg\documentclass[12pt]{minimal}
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\begin{document}$$\cdot $$\end{document}· yr) (90% CL). This corresponds to a total production rate of \documentclass[12pt]{minimal}
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\begin{document}$$^{77}$$\end{document}77Ge and \documentclass[12pt]{minimal}
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\begin{document}$$^{77\textrm{m}}$$\end{document}77mGe of \documentclass[12pt]{minimal}
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\begin{document}$$<{0.38}$$\end{document}<0.38 nuc/(kg\documentclass[12pt]{minimal}
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\begin{document}$$\cdot $$\end{document}· yr) (90% CL), assuming equal production rates. A previous Monte Carlo study predicted a value for in-situ \documentclass[12pt]{minimal}
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\begin{document}$$^{77}$$\end{document}77Ge and \documentclass[12pt]{minimal}
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\begin{document}$$^{77\textrm{m}}$$\end{document}77mGe 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 \documentclass[12pt]{minimal}
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\begin{document}$$^{77\textrm{m}}$$\end{document}77mAs can be utilised to further suppress the \documentclass[12pt]{minimal}
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\begin{document}$$^{77}$$\end{document}77Ge 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.