New limit for the half-life of double beta decay of $^{94}$Zr to the first excited state of $^{94}$Mo

TL;DR

This study sets a new lower limit on the half-life of double beta decay of $^{94}$Zr to an excited state of $^{94}$Mo, improving previous experimental bounds and contributing to understanding neutrino properties.

Contribution

The paper provides the most stringent experimental lower limit on the half-life of $^{94}$Zr double beta decay to the first excited state, using a low-background detector and extended exposure.

Findings

No evidence of decay was observed.

Lower half-life limit improved by a factor of 4.

Estimated sensitivity of the experiment is $2.0 imes 10^{19}$ years.

Abstract

Neutrinoless Double Beta Decay is a phenomenon of fundamental interest in particle physics. The decay rates of double beta decay transitions to the excited states can provide input for Nuclear Transition Matrix Element calculations for the relevant two neutrino double beta decay process. It can be useful as supplementary information for the calculation of Nuclear Transition Matrix Element for the neutrinoless double beta decay process. In the present work, double beta decay of $^{94}$Zr to the $2^{+}_{1}$ excited state of $^{94}$Mo at 871.1 keV is studied using a low background $\sim$ 230 cm$^3$ HPGe detector. No evidence of this decay was found with a 232 g.y exposure of natural Zirconium. The lower half-life limit obtained for the double beta decay of $\rm^{94}Zr$ to the $2^{+}_{1}$ excited state of $\rm^{94}Mo$ is $T_{1/2} (0\nu + 2\nu)> 3.4 \times 10^{19}$ y at 90% C.L., an improvement by a factor of $\sim$ 4 over the existing experimental limit at 90\% C.L. The sensitivity is estimated to be $T_{1/2} (0\nu + 2\nu) > 2.0\times10^{19}$ y at 90% C.L. using the Feldman-Cousins method.