Core polarization effects on spin-dipole and first-forbidden β-decay operators in the lead region

The effect of two-particle–two-hole ground-state correlations on spin-dipole transitions and the similar first-forbidden β-decay transitions is studied for nuclei in the lead region with realistic shell-model interactions. Transitions are considered between states for which one is a particle-hole excitation of the other. It is found that the tensor component of the residual interaction is quite important for the $0^{\mathrm{-}}$ and $1^{\mathrm{-}}$ spin-dipole transitions and the analogous β-decay matrix elements. It is destructive for $0^{\mathrm{-}}$ and constructive for $1^{\mathrm{-}}$ so that the quenching of the two modes is quite different. The atypical 1${\mathit{g}}_{9/2}$→0${\mathit{h}}_{9/2}$ transition is described. The results are compared to previous determinations.