Final Results of GERDA on the Two-Neutrino Double-β Decay Half-Life of 76Ge

We present the measurement of the two-neutrino double-β decay rate of ⁷⁶Ge 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: T₁^{/2 2 ν}=(2.022 ±0.01 8_stat±0.03 8_syst)×10²¹ yr . This is the most precise determination of the ⁷⁶Ge two-neutrino double-β decay half-life and one of the most precise measurements of a double-β decay process. The relevant nuclear matrix element can be extracted: M_eff^{2 ν}=(0.101 ±0.001 ) .