We present the measurement of the two-neutrino double-$\mathrm{<ruby><rb>\beta </rb><rt>べーた</rt></ruby>}$ decay rate of ${}^{76}\mathrm{Ge}$ performed with the GERDA Phase II experiment. With a subset of the entire GERDA exposure, 11.8 kg yr, the half-life of the process has been determined: $T_{1/2}^{2\mathrm{<ruby><rb>\nu </rb><rt>にゅー</rt></ruby>}}=(2.022\pm 0.018_{\mathrm{stat}}\pm 0.038_{\mathrm{syst}})\times {10}^{21}\mathrm{yr}$. This is the most precise determination of the ${}^{76}\mathrm{Ge}$ two-neutrino double-$\mathrm{<ruby><rb>\beta </rb><rt>べーた</rt></ruby>}$ decay half-life and one of the most precise measurements of a double-$\mathrm{<ruby><rb>\beta </rb><rt>べーた</rt></ruby>}$ decay process. The relevant nuclear matrix element can be extracted: ${\mathcal{M}}_{\mathrm{eff}}^{2\mathrm{<ruby><rb>\nu </rb><rt>にゅー</rt></ruby>}}=(0.101\pm 0.001)$.

• Received 13 May 2023
• Accepted 15 August 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.142501

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

Published by the American Physical Society