Excitation functions at 175° (lab) for elastic scattering of ${\pi }^{+}$ from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ have been measured across the energy region of the pion-nucleon (3,3) resonance. Optical-model calculations with matter distributions deduced from electron scattering qualitatively reproduce the data, but better agreement can be obtained with suitable modifications. These modifications may indicate the effects of the nuclear medium on the basic pion-nucleon interaction.

• Received 6 October 1986

DOI:https://doi.org/10.1103/PhysRevC.35.1148