Elastic scattering ofπ+andπ−fromCa40at 64.8 MeV

Angular distributions of ${\pi }^{+}$ and ${\pi }^{-}$ elastic scattering on ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ at 64.8 MeV are presented. The data are analyzed using a first-order, nonlocal optical model based on a Kisslinger $t$ matrix with an off-shell form factor. This model is unable to fit the data for any value of the off-shell parameter $\alpha$ unless the nuclear matter radius is allowed to vary from that derived from electron scattering. The resulting best-fit radii are as much as 0.40 fm larger than the electron scattering value for ${\pi }^{+}$ and 0.55 fm larger for ${\pi }^{-}$. For a given $\alpha$ the ${\pi }^{-}$ best fit radius is also consistently larger by about 0.2 fm than that for ${\pi }^{+}$. In addition, the fits show no significant preference for any value of $\alpha$ between 400 and 900 MeV/c. Inclusion of the normally omitted second-order potential terms in the optical model does not significantly alter the results.