New evidence for meson-exchange-current enhancement of isovector M1 strength

We report here isovector M1 strength distributions in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ obtained in a high-resolution (e,e’) experiment at the Darmstadt Electron Linear Accelerator. The M1 strength is strongly enhanced relative to the Gamow-Teller strength for analog transitions observed in recent (p,n) and (n,p) experiments at the Indiana University Cyclotron Facility and TRIUMF. We show that this enhancement can likely be attributed to meson-exchange contributions to the spin part of the M1 operator.