Role ofρ2term in pion-nucleus dynamics

Abstract

We study the corrections to the first-order optical potential in $\ensuremath{\pi}$-nucleus elastic scattering from 28 to 260 MeV. The dynamical effects of true pion absorption (and correlations) are incorporated into our analysis through the inclusion of a second-order optical potential. We have performed a ${\ensuremath{\chi}}^{2}$ fit to the measured $\ensuremath{\pi}\ensuremath{-}^{4}\mathrm{He}$ and $\ensuremath{\pi}\ensuremath{-}^{12}\mathrm{C}$ elastic differential cross sections in order to determine a parametrization of the second-order optical potential. It is shown that the inclusion of these higher-order effects not only yields excellent fits to the low-energy data (50 MeV), but also systematically improves calculated cross sections at the larger angles in the resonance region. We also find a general improvement in the agreement between the calculated and measured total cross sections, in particular at low energies. Since our first-order potential is essentially parameter free, we believe that the parameters of the second-order potential determined from the present work are meaningful and may serve as a useful guide in future microscopic analyses.NUCLEAR REACTIONS Pion-helium and pion-carbon scattering (28-260 MeV). Role of second-order optical potential.