The pion single-charge-exchange reactions ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}({\pi }^{\pm }, {\pi }^0)$ were measured at 164 MeV in the angular range 0° to 30°. The spectra show pronounced peaks at energies corresponding to the analog states of the isovector electric dipole resonance in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. The maximum (${\pi }^{-}, {\pi }^0$) cross section is 1.69±0.24 times the (${\pi }^{+}, {\pi }^0$) cross section. The measured angular distribution shapes and magnitudes are quite well described by distorted-wave impulse-approximation calculations based on the Goldhaber-Teller transition density.

• Received 19 July 1982

DOI:https://doi.org/10.1103/PhysRevLett.49.1376