New Half-life Limits on Double Beta Decays of Pd110 and Pd102 into Excited States

TL;DR

This study sets new lower bounds on the half-lives of double beta decay and electron capture in Pd110 and Pd102, improving previous limits and providing first constraints for certain excited states using underground HPGe detectors.

Contribution

It provides the first experimental lower half-life limits for all excited states in Pd110 and Pd102 and improves existing bounds by over three times.

Findings

No signal detected in the search.

Lower half-life limits established for specific excited states.

First experimental limits for all excited states in Pd110 and Pd102.

Abstract

A search for excited state transitions of double beta decay in Pd110 and double electron capture in Pd102 has been performed in the HADES underground laboratory with two low background HPGe detectors in sandwich configuration. After an exposure of 35.92 kg*d, no signal was found. The frequentist spectral analysis resulted in lower half-life limits of 1.98e20 yr and 1.72e20 yr (95% CL) for the first 0+ and 2+ excited state in Pd110 respectively. This is an improvement by more than a factor of 3 with respect to previous measurements. In Pd102, the lower half-life limit could be improved to 5.95e18 yr (95% CL) for the first 0+ excited state. Furthermore, first experimental lower half-live limits are found for all possible excited states in the Pd110 and Pd102 systems.