Distorted-wave impulse approximation and coupled-channels analysis of inelastic pion scattering from 18O.

Abstract

Data for inelastic pion scattering from $^{18}\mathrm{O}$ at ${T}_{\ensuremath{\pi}}$=164 MeV, exciting the lowest ${2}^{+}$, ${3}^{\mathrm{\ensuremath{-}}}$, and ${1}^{\mathrm{\ensuremath{-}}}$ states, were analyzed by distorted-wave impulse approximation and coupled-channel calculations using transition densities derived from shell model calculations. Coupled-channels effects were found to be relatively unimportant for the ${2}^{+}$ and ${3}^{\mathrm{\ensuremath{-}}}$ states, but non-negligible for the excitation of the ${1}^{\mathrm{\ensuremath{-}}}$ state. Nevertheless, the inclusion of multistep excitation paths is not sufficient to generate a fit to the ${1}^{\mathrm{\ensuremath{-}}}$ data with the shell model wave functions. Major modifications are needed in the radial dependence of the neutron and proton parts of the transition density for the ${0}^{+}$\ensuremath{\rightarrow}${1}^{\mathrm{\ensuremath{-}}}$ one-step process.