Isobaric Analog States in Pion Single-Charge-Exchange Reactions on and above the (3,3) Resonance Energy

The 0° differential cross sections of (${\pi }^{+}$, ${\pi }^0$) reactions on a series of nuclei to isobaric analog states were determined at 165, 230, and 295 MeV. For each energy, the $A$ dependence is well described by a power law of the form $\sigma =g\left(E\right)\mathrm{}(N-Z)\mathrm{}{A}^{-\alpha \mathrm{}\left(E\right)\mathrm{}}$, where $\alpha \mathrm{}\left(E\right)\mathrm{}$ is a decreasing function of energy. The 0° excitation functions peak around the (3,3) resonance energy for all nuclei except ${}_{}{}^{90}{}_{}{}^{}\mathrm{Zr}$. A possible explanation in terms of neutron and proton densities is discussed.