New Limits on Double Electron Capture of $^{40}$Ca and $^{180}$W

TL;DR

This paper reports new experimental limits on double electron capture processes in isotopes $^{40}$Ca and $^{180}$W using data from the CRESST-II experiment, significantly improving previous bounds.

Contribution

It provides the first limits on double electron capture in $^{40}$Ca and $^{180}$W from the CRESST-II data, enhancing the sensitivity of such searches.

Findings

Established new half-life limits for $^{40}$Ca and $^{180}$W.

Improved existing limits by factors of 1.4 to 30.

Used 730 kg days of low-background data.

Abstract

We analyzed low-background data from the CRESST-II experiment with a total net exposure of 730 kg days to extract limits on double electron capture processes. We established new limits for $^{40}$Ca with $T_{1/2}^{2v2K}>9.9\times10^{21}$ y and $T_{1/2}^{0v2EC}>1.4\times10^{22}$ y and for $^{180}$W with T$_{1/2}^{2v2K}>3.1\times10^{19}$ y and $T_{1/2}^{0v2EC}>9.4\times10^{18}$ y at 90% CL. Depending on the process, these values improve the currently best limits by a factor of $\sim$1.4-30.