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

TL;DR

This study used radiopure ZnWO4 crystal scintillators at Gran Sasso to search for double beta decay in zinc and tungsten isotopes, setting new half-life limits and improving constraints on rare decay processes.

Contribution

It provides the first experimental limits on several double beta decay modes in zinc and tungsten isotopes using ZnWO4 scintillators, enhancing the sensitivity of such searches.

Findings

Established new half-life limits on double beta decay modes of 64Zn, 70Zn, 180W, and 186W.

Set constraints on resonant neutrinoless double electron capture in 180W.

Improved the half-life limit on alpha decay of 183W to 179Hf.

Abstract

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 yr. New improved half-life limits on the double beta decay modes of 64Zn, 70Zn, 180W, and 186W 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 64Zn have been set: T_{1/2}(2\nu 2K) > 1.1 10^{19} yr, T_{1/2} (0\nu 2\epsilon) > 3.2 10^{20} yr, T_{1/2} (2\nu \epsilon \beta^+) > 9.4 10^{20} yr, and T_{1/2} (0\nu \epsilon \beta^+) > 8.5 10^{20} yr, all at 90% C.L. Resonant neutrinoless double electron capture in 180W has been restricted on the level of T_{1/2} (0\nu 2\epsilon) > 1.3 10^{18} yr. A new half-life limit on alpha transition of 183W to the metastable excited level 1/2^- 375 keV of 179Hf has been established: T_{1/2} > 6.7 10^{20} yr.