Investigation of Internal Isospin Mixing of Isobaric Analog Resonances from Polarized-Proton Experiments

The lowest analog resonances in ${}_{}{}^{89}{}_{}{}^{}\mathrm{Y}$, ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$, ${}_{}{}^{91}{}_{}{}^{}\mathrm{Nb}$, and ${}_{}{}^{93}{}_{}{}^{}\mathrm{Nb}$ have been investigated with polarized protons. The consistent fit of the direct and compound-nucleus contributions to both resonance and background scattering for the elastic proton and the neutron decay channels yields an internal spreading width ${\Gamma }_{\mathrm{int}}\downarrow =12\mathrm{}\pm 3$ keV.