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

TL;DR

This study searched for double beta decay in $^{106}$Cd using an enriched scintillator and counters, setting new half-life limits around 10^{20}-10^{22} years, with no observed decay events.

Contribution

First to use an enriched $^{106}$CdWO$_4$ scintillator with coincidence detection to improve limits on $^{106}$Cd double beta decay modes.

Findings

No decay signals observed over 26033 hours.

Set new half-life limits at $ ext{level of } 10^{20}-10^{22}$ years.

Sensitivity approaches theoretical decay half-life predictions.

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, $T^{2\nu\mathrm{EC}\beta^+}_{1/2}\geq2.1\times 10^{21}$ 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 $T_{1/2}\sim10^{21}-10^{22}$ yr. The resonant neutrinoless double-electron capture to the 2718 keV excited state of $^{106}$Pd is restricted at the level of $T^{0\nu\mathrm{2K}}_{1/2}\geq2.9\times10^{21}$ yr