Eur. Phys. J. A (2026) 62: 124
https://doi.org/10.1140/epja/s10050-026-01899-0

Regular Article - Theoretical Physics

Large-scale shell-model investigation of $2\nu$ECEC in $_{}^{132}$Ba and $_{}^{78}$Kr

Department of Physics, Indian Institute of Technology Roorkee, 247 667, Roorkee, India

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Received: 4 January 2026
Accepted: 6 June 2026
Published online: 24 June 2026

Abstract

We present a theoretical investigation of two-neutrino double electron capture ($2\nu$ECEC) in $_{}^{132}$Ba and $_{}^{78}$Kr based on large-scale shell-model calculations. The nuclear matrix elements (NMEs) for the $2\nu$ECEC process in $_{}^{132}$Ba and $_{}^{78}$Kr are calculated using the SN100PN and GWBXG effective interactions, respectively. The reliability of the employed interactions is first examined through a comparison of the calculated and experimental spectroscopic properties of the parent, intermediate, and granddaughter nuclei involved in the decay. We also examine the cumulative contribution of the $2\nu$ECEC NME with respect to the $1^{+}$ state energies in the intermediate nuclei. The present results provide an updated and improved shell-model estimate of the $2\nu$ECEC NME and half-life for $_{}^{78}$Kr relative to earlier studies, and a baseline theoretical prediction for $_{}^{132}$Ba that may assist future experimental efforts in constraining this rare decay mode.