Enhancement of the isovectorM1strength in28Si due to meson exchange currents

Meson exchange currents (MEC’s) can induce an enhancement of the $B\left(M1\mathrm{}\right)\mathrm{}$ strength in nuclei over the corresponding Gamow-Teller strength. Such an increase was observed in ${}^{28}$Si [C. Lüttge et al., Phys. Rev. C 53, 127 (1996)], but the experimental ratio was much larger than shell model predictions using the unified $\mathrm{sd}$-shell interaction and corrections to the $g$ factors which incorporate MEC effects. It is pointed out that, when taking the Gamow-Teller strength from a reanalysis of the ${}^{28}$Si$\mathrm{}(p,n)\mathrm{}$ data as well as from a recent ${}^{28}{\mathrm{S}\mathrm{i}(}^3\mathrm{H}\mathrm{e},t)$ experiment, the derived ratio is now in good agreement with the shell model results. This finding provides strong support that the observed enhancement is due to meson exchange currents.