Final results of an experiment to search for 2β processes in zinc and tungsten with the help of radiopure ZnWO4 crystal scintillators

A search for the double beta decay of zinc and tungsten isotopes has been performed with the help of radiopure ZnWO4 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 x yr. New improved half-life limits on the double beta decay modes of Zn-64, Zn-70, W-180 and W-186 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 Zn-64 have been set: T-1/2(2 nu 2K) >= 1.1 x 10(19) yr, T-1/2(0 nu 2 epsilon) >= 3.2 x 10(20) yr, T-1/2(2 nu epsilon beta+) >= 9.4 x 10(20) yr and T-1/2(0 nu epsilon beta+) >= 8.5 x 10(20) yr all at 90% CL. Resonant neutrinoless double electron capture in W-180 has been restricted on the level of T-1/2(0 nu 2 epsilon) >= 1.3 x 10(18) yr. A new half-life limit on alpha transition of W-183 to the metastable excited level 1/2(-) 375 keV of Hf-179 has been established: T-1/2 >= 6.7 x 10(20) yr.