Search for $2β$ decay of $^{106}$Cd with enriched $^{106}$CdWO$_4$ crystal scintillator in coincidence with four HPGe detectors

Abstract

A radiopure cadmium tungstate crystal scintillator, enriched in 106 Cd to 66%, with mass of 216 g ( 106 CdWO 4 ), was used to search for double beta decay processes in 106 Cd in coincidence with four ultra-low background high purity germanium detectors in a single cryostat. New improved limits on the double beta processes in 106 Cd have been set on the level of 10 20 − 10 21 yr after 13085 h of data taking. In particular, the half-life limit on the two neutrino electron capture with positron emission, T 2νεβ + 1/2 ≥ 1.1 × 10 21 yr, has reached the region of theoretical predictions. With this half-life limit the effective nuclear matrix element for the 2νεβ + decay is bounded as M 2νεβ + ef f ≤ 1.1. The resonant neutrinoless double electron captures to the 2718 keV, 2741 keV and 2748 keV excited states of 106 Pd are restricted at the level of T 1/2 ≥ (8.5 × 10 20 − 1.4 × 10 21 ) yr.

RES-NOVA sensitivity to core-collapse and failed core-collapse supernova neutrinos

“…This crystal features extremely low concentration of radioactive impurities (i.e. 238 U, 232 Th and 210 Pb) when archaeological Pb is used, as demonstrated in [49,50]. In addition, PbWO 4 is a widely developed crystal for high energy physics applications as major component for electromagnetic calorimeters (e.g.…”