Final results on ${}^{\text{82}}$Se double beta decay to the ground state of ${}^{\text{82}}$Kr from the NEMO-3 experiment

Abstract

Using data from the NEMO-3 experiment, we have measured the two-neutrino double beta decay ($2\hat{I}½{\hat{I}}^2{\hat{I}}^2$) half-life of ${}^{82}$Se as $T_{1/2}^{2ν} = \left[ 9.39 \pm 0.17\,\left(\mbox{stat}\right) \pm 0.58\,\left(\mbox{syst}\right)\right] \times 10^{19}$ y under the single-state dominance hypothesis for this nuclear transition. The corresponding nuclear matrix element is $\left|M^{2\hat{I}½}\right|=0.0498\pm 0.0016$. In addition, a search for neutrinoless double beta decay ($0\hat{I}½{\hat{I}}^2{\hat{I}}^2$) using 0.93 kg of ${}^{82}$Se observed for a total of 5.25 y has been conducted and no evidence for a signal has been found. The resulting half-life limit of $T_{1/2}^{0ν} > 2.5 \times 10^{23} \,\mbox{y} \,(90\%\,\mbox{C.L.})$ for the light neutrino exchange mechanism leads to a constraint on the effective Majorana neutrino mass of $\langle m_ν \rangle < \left(1.2 - 3.0\right) \,\mbox{eV}$, where the range reflects $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ nuclear matrix element values from different calculations. Furthermore, constraints on lepton number violating parameters for other $0\hat{I}½{\hat{I}}^2{\hat{I}}^2$ mechanisms, such as right-handed currents, majoron emission and R-parity violating supersymmetry modes have been set.

14 pages, 10 figures