Two-neutrino double-β decay measurement of ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$

From data accumulated over 6140 h with 172 g of enriched molybdenum (1.18 mol yr of ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$) with the NEMO 2 detector in the Fréjus Underground Laboratory, a clear ββ2ν signal (1433 events) is observed, leading to a half-life ${\mathit{T}}_{1/2}$=0.95±0.04(stat)±0.09(syst) ${10}^{19}$ yr. The experimental two-electron energy spectrum and the two-electron angular distribution are in agreement with the expected ones. Limits for ββ0ν decays to the ground state, excited states ($2_1^{+}$ and $0_1^{+}$), and also with Majoron emission are given.