Final results of an experiment to search for 2β processes in zinc and tungsten with the help of radiopure ZnWO4crystal scintillators

A search for the double beta decay of zinc and tungsten isotopes has been performed with the help of radiopure ZnWO 4 crystal scintillators (0.1–0.7 kg) at the Gran Sasso National Laboratories of the INFN. The total exposure of the low background measurements is 0.529 kg × yr. New improved half-life limits on the double beta decay modes of 64 Zn, 70 Zn, 180 W and 186 W have been established at the level of 10 18 –10 21 yr. In particular, limits on double electron capture and electron capture with positron emission in 64 Zn have been set: T 2ν2 K 1/2 ⩾ 1.1 × 10 19 yr, T 0ν2ε 1/2 ⩾ 3.2 × 10 20 yr, T 2νεβ + 1/2 ⩾ 9.4 × 10 20 yr and T 0νεβ + 1/2 ⩾ 8.5 × 10 20 yr all at 90% CL. Resonant neutrinoless double electron capture in 180 W has been restricted on the level of T 0ν2ε 1/2 ⩾ 1.3 × 10 18 yr. A new half-life limit on α transition of 183 W to the metastable excited level 1/2 − 375 keV of 179 Hf has been established: T 1/2 ⩾ 6.7 × 10 20 yr.