Two-neutrino double-β decay measurement ofMo100

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 Fr\'ejus Underground Laboratory, a clear \ensuremath{\beta}\ensuremath{\beta}2\ensuremath{\nu} signal (1433 events) is observed, leading to a half-life ${\mathit{T}}_{1/2}$=0.95\ifmmode\pm\else\textpm\fi{}0.04(stat)\ifmmode\pm\else\textpm\fi{}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 \ensuremath{\beta}\ensuremath{\beta}0\ensuremath{\nu} decays to the ground state, excited states (${2}_{1}^{+}$ and ${0}_{1}^{+}$), and also with Majoron emission are given.