Search for 2K(2\nu)-capture of Kr-78

TL;DR

This study searches for double K-capture in Kr-78 using high-pressure counters, observing a potential signal with a half-life around 1.4 x 10^{22} years, indicating possible rare nuclear decay.

Contribution

It presents the first experimental search for 2K(2 u)-capture in Kr-78 using a novel method with enriched krypton and reports a potential detection.

Findings

Observed an excess of events possibly indicating 2K-capture in Kr-78.

Estimated half-life for the process as approximately 1.4 x 10^{22} years.

Provides experimental limits and evidence for rare nuclear decay in krypton.

Abstract

Results of a search for Kr-78 double K-capture at the second stage of the experiment with high-pressure copper proportional counters are presented. The method is based on comparison of spectra measured with natural and enriched krypton. The total exposure of the low background measurements is for Kr-78 152 g*yr and for Kr-nat 106 g*yr. An excess of events was observed in the analysis of Kr-78 selected data collected during 2008-2010 years. This excess could correspond to a double K-capture of Kr-78 with the half-life of T_{1/2}(2K,2\nu + 0\nu)=[1.4^{+2.2}_{-0.7}]\cdot 10^{22}$ yr (90% C.L.)