Elastic Scattering of 50-MeVπ+fromC12

Results for the elastic scattering of 50-MeV ${\pi }^{+}$ on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ are presented. Contrary to experience at energies above 100 MeV, simple optical models (with parameters derived from $\pi -N$ phase shifts) give poor fits to the data. Forcing good fits yields potentials that are pion producing or in violation of unitarity. We conclude that improved optical potentials will be required to describe low-energy data.