Search for $2\beta$ decay of {106}$Cd with an enriched {106}$CdWO$_4$ crystal scintillator in coincidence with four HPGe detectors
A radiopure cadmium tungstate crystal scintillator, enriched in Cd106 to 66% with mass of 216 g (Cd106WO4) was used to search for double b decay processes in Cd106 in coincidence with four ultra low background high purity germanium detectors in a single cryostat. Improved limits on the double b processes in Cd106 have been set on the level of 1020 1021 yr after 13 085 h of data taking. In particular, the half life limit on the two neutrino electron capture with positron emission, T2neb+1/2>=1.1x1021 yr, has reached the region of theoretical predictions. With this half life limit the effective nuclear matrix element for the 2neb+ decay is bounded as M2neb+eff<=1.1. The resonant neutrinoless double electron captures to the 2718 2741 and 2748 keV excited states of Pd106 are restricted at the level of T1/2>(8.5x1020 1.4x1021) yr.