Pion single charge exchange onLi7at low energies

Forward-angle differential cross sections for the isobaric-analog-state transition, ${}_{}{}^7{}_{}{}^{}$Li(${\pi }^{+}$,${\pi }^0$ ${)}^7$Be, were measured at 33.5, 41.1, 48.7, and 58.8 MeV. A minimum in the excitation function of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ at 42.3±1 MeV reflects the analogous minimum in the free πN cross section, which, according to current phase-shift analyses, is between 45 and 50 MeV. The data are compared with optical-model calculations.