Measurement of the $2 u\beta\beta$ Decay Half-Life and Search for the $0 u\beta\beta$ Decay of $^{116}$Cd with the NEMO-3 Detector

摘要

The NEMO-3 experiment measured the half-life of the $2\nu\beta\beta$ decayand searched for the $0\nu\beta\beta$ decay of $^{116}$Cd. Using $410$ g of$^{116}$Cd installed in the detector with an exposure of $5.26$ y,($4968\pm74$) events corresponding to the $2\nu\beta\beta$ decay of $^{116}$Cdto the ground state of $^{116}$Sn have been observed with a signal tobackground ratio of about $12$. The half-life of the $2\nu\beta\beta$ decay hasbeen measured to be $T_{1/2}^{2\nu}=[2.74\pm0.04\mbox{(stat.)}\pm0.18\mbox{(syst.)}]\times10^{19}$y. No events have been observed above the expected background while searchingfor $0\nu\beta\beta$ decay. The corresponding limit on the half-life isdetermined to be $T_{1/2}^{0\nu} \ge 1.0 \times 10^{23}$ y at the $90$ % C.L.which corresponds to an upper limit on the effective Majorana neutrino mass of$\langle m_{\nu} \rangle \le 1.4-2.5$ eV depending on the nuclear matrixelements considered. Limits on other mechanisms generating $0\nu\beta\beta$decay such as the exchange of R-parity violating supersymmetric particles,right-handed currents and majoron emission are also obtained.