Search for double beta decay of ${}^{106}$Cd with an enriched ${}^{106}$CdWO${}_4$ crystal scintillator in coincidence with CdWO${}_4$ scintillation counters

Abstract

Studies on double beta decay processes in ${}^{106}$Cd were performed by using a cadmium tungstate scintillator enriched in ${}^{106}$Cd at 66% (${}^{106}$CdWO${}_4$) with two CdWO${}_4$ scintillation counters (with natural Cd composition). No effect was observed in the data accumulated over 26033 h. New improved half-life limits were set on the different channels and modes of the ${}^{106}$Cd double beta decay at level of $\lim T_{1/2}\sim 10^{20}-10^{22}$ yr. The limit for the two neutrino electron capture with positron emission in ${}^{106}$Cd to the ground state of ${}^{106}$Pd, $T^{2ν\mathrm{EC}β^+}_{1/2}\geq2.1\times 10^{21}$ yr, was set by the analysis of the ${}^{106}$CdWO${}_4$ data in coincidence with the energy release 511 keV in both CdWO${}_4$ counters. The sensitivity approaches the theoretical predictions for the decay half-life that are in the range $T_{1/2}\sim 10^{21}-10^{22}$ yr. The resonant neutrinoless double-electron capture to the 2718 keV excited state of ${}^{106}$Pd is restricted at the level of $T_{1/2}^{0\hat{I}½2K}\ge 2.9\times 10^{21}$ yr

16 pages, 10 figures, 2 tables