Shell-model description for the first-forbidden $\beta^-$ decay of $^{207}$Hg into the one-proton-hole nucleus $^{207}$Tl

Abstract

In this work, we have performed large-scale shell-model calculations for the first-forbidden $\beta ^{-}$ decay of $^{207}$Hg into the one-proton-hole nucleus $^{207}$Tl corresponding to the recently available experimental data from ISOLDE-CERN [T. A. Berry et al., Phys. Rev. C 101, 054311 (2020)]. We have used the one-particle one-hole ($1p$-$1h$) truncation for both protons and neutrons simultaneously across the doubly-shell closure at $^{208}$Pb in the final states of $^{207}$Tl. In our calculations, we have also considered the effect of mesonic enhancement $\epsilon _{\mathrm{mec}}=2.01\pm 0.05$ in the rank-0 for the axial-charge matrix element $\gamma _{5}$. Here, we have calculated the $\log ft$ values from the ground-state of $^{207}$Hg to the several excited states of $^{207}$Tl and obtained a good agreement between the calculated and the experimental data. In the experimental data spin and parity for some states are not yet confirmed, thus based on the shell-model results for the $\log ft$ values we have given the prediction for these states. This is the first theoretical calculation for the $\log ft$ values for these transitions.