Final results of the Aurora experiment to study 2${\hat{I}}^2$ decay of ${}^{116}$Cd with enriched ${}^{116}$CdWO${}_4$ crystal scintillators

Abstract

The double-beta decay of ${}^{116}$Cd has been investigated with the help of radiopure enriched ${}^{116}$CdWO${}_4$ crystal scintillators (mass of 1.162 kg) at the Gran Sasso underground laboratory. The half-life of ${}^{116}$Cd relatively to the $2\nu 2{\hat{I}}^2$ decay to the ground state of ${}^{116}$Sn was measured with the highest up-to-date accuracy as $T_{1/2}=(2.63_{-0.12}^{+0.11})\times 10^{19}$ yr. A new improved limit on the 0$\hat{I}½$2${\hat{I}}^2$ decay of ${}^{116}$Cd to the ground state of ${}^{116}$Sn was set as $T_{1/2}\ge 2.2\times 10^{23}$ yr at 90\% C.L., which is the most stringent known restriction for this isotope. It corresponds to the effective Majorana neutrino mass limit in the range $⟨m_{\hat{I}}½⟩\le (1.0-1.7)$ eV, depending on the nuclear matrix elements used in the estimations. New improved half-life limits for the 0$\hat{I}½$2${\hat{I}}^2$ decay with majoron(s) emission, Lorentz-violating $2\nu 2{\hat{I}}^2$ decay and $2{\hat{I}}^2$ transitions to excited states of ${}^{116}$Sn were set at the level of $T_{1/2}\ge 10^{20}-10^{22}$ yr. New limits for the hypothetical lepton-number violating parameters (right-handed currents admixtures in weak interaction, the effective majoron-neutrino coupling constants, R-parity violating parameter, Lorentz-violating parameter, heavy neutrino mass) were set.

30 pages, 17 figures and 7 tables