Search for double beta decay of zinc and tungsten with low background ZnWO 4 crystal scintillators

Abstract

Double beta processes in 64Zn, 70Zn, 180W, and 186W have been searched for with the help of large volume (0.1–0.7 kg) low background ZnWO 4 crystal scintillators at the Gran Sasso National Laboratories of the INFN (Italy). The total measurement time exceeds ten thousand hours. New improved half-life limits on double electron capture and electron capture with positron emission in 64Zn have been set, in particular (all the limits are at 90% C.L.): T 1 / 2 0 ν 2 ε ⩾ 1.1 × 10 20 yr , T 1 / 2 2 ν ε β + ⩾ 7.0 × 10 20 yr , and T 1 / 2 0 ν ε β + ⩾ 4.3 × 10 20 yr . In addition, new T 1 / 2 bounds were set for different modes of 2 β processes in 70Zn, 180W, and 186W at the level of 10 17–10 20 yr.