Search for $\beta^+$EC and ECEC processes in $^{112}$Sn

TL;DR

This study sets new experimental limits on rare double electron capture and positron emission processes in tin-112, exploring potential decay enhancements and discussing future research prospects.

Contribution

It provides the first experimental half-life limits for $eta^+$EC and ECEC processes in $^{112}$Sn, including a specific limit for ECEC(0$ u$) to an excited state.

Findings

Half-life limit of $4.7 imes 10^{20}$ years for ECEC(0$ u$) in $^{112}$Sn

Limits on other $eta^+$EC and ECEC processes between $(0.6-8.7) imes 10^{20}$ years

Discussion on possible decay rate enhancement due to near-degeneracy with excited states

Abstract

Limits on $\beta^+$EC (here EC denotes electron capture) and ECEC processes in $^{112}$Sn have been obtained using a 380 cm$^3$ HPGe detector and an external source consisting of 53.355 g enriched tin (94.32% of $^{112}$Sn). A limit with 90% C.L. on the $^{112}$Sn half-life of $4.7\times 10^{20}$ y for the ECEC(0$\nu$) transition to the $0^+_3$ excited state in $^{112}$Cd (1871.0 keV) has been established. This transition is discussed in the context of a possible enhancement of the decay rate by several orders of magnitude given that the ECEC$(0\nu)$ process is nearly degenerate with an excited state in the daughter nuclide. Prospects for investigating such a process in future experiments are discussed. The limits on other $\beta^+$EC and ECEC processes in $^{112}$Sn were obtained on the level of $(0.6-8.7)\times 10^{20}$ y at the 90% C.L.