Inelastic proton scattering at energies of a few hundred million electron volts and extreme forward angles selectively excite the isovector spin-flip $M1$ ($\mathrm{IVS}M1$) resonance. A method based on isospin symmetry is presented to extract its electromagnetic transition strength from the $(p,p^{\prime })$ cross sections. It is applied to ${}^{48}\mathrm{Ca}$, a key case for an interpretation of the quenching phenomenon of the spin-isospin response, and leads to a $M1$ strength consistent with an older $(e,e^{\prime })$ experiment excluding the almost two times larger value from a recent $(\gamma ,n)$ experiment. Good agreement with electromagnetic probes is observed in ${}^{208}\mathrm{Pb}$, suggesting the possibility of extracting systematic information on the IVSM1 resonance in heavy nuclei.

• Received 9 October 2015
• Revised 7 January 2016

DOI:https://doi.org/10.1103/PhysRevC.93.041302