Pauli-principle effects in pion scattering from the lightest nuclei

We investigate the effect of the Pauli principle in π-nucleus scattering. Descriptions are made in terms of the optical potential based on the multiple scattering formalism and a prescription is given for incorporating the Pauli effect. Detailed examinations are performed for π-d, ${\mathrm{-}}^3$He, and ${\mathrm{-}}^4$He scattering in the energy range $T_{\pi }$=50–300 MeV. The Pauli effect is found to cause an important medium correction in both low and intermediate energy regions, and this aspect is emphasized for the more strongly correlated nucleus. Attention is paid to the πN partial wave mixing. It is seen that the mixing between the $P_{33}$ and the other partial waves gives a non-negligible contribution throughout the energy range considered.