An improved half-life limit of the double beta decay of $^{94}$Zr into the excited state of $^{94}$Mo

TL;DR

This study conducted a sensitive search for double beta decay of $^{94}$Zr into an excited state of $^{94}$Mo, setting a new lower half-life limit that improves previous bounds by 50% using underground gamma spectroscopy.

Contribution

The paper reports the first improved half-life limit for $^{94}$Zr double beta decay into excited states, enhancing the sensitivity of previous measurements by 50%.

Findings

No decay signal observed.

New lower half-life limit: $5.2\times10^{19}$ years.

Limit applies to both $0\nu\beta\beta$ and $2\nu\beta\beta$ modes.

Abstract

A search for the double beta decay transition of $^{94}$Zr into the first excited state of $^{94}$Mo has been performed at the Felsenkeller underground laboratory in Dresden, Germany. A 341.1 g zirconium sample with natural isotopic composition has been measured for 43.9 d in an ultra low background gamma spectroscopy setup. No signal has been observed and a new best lower half-life limit is set as $5.2\times10^{19}$ yr (90% CI). This limit is valid for the $0\nu\beta\beta$ and $2\nu\beta\beta$ decay into excited states of $^{94}$Mo but cannot distinguish between the two modes. Existing limits are improved by 50%.