Pion inelastic scattering to giant resonances and low-lying collective states inSn118andCa40

Abstract

A comparison of differential cross sections for inelastic scattering of 130 MeV positive and negative pions has been made for studying the giant resonance region in ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$ and ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$. In addition, several of the low-lying collective states in each target were examined. Comparison to distorted wave impulse approximation calculations allowed collective deformation lengths βR and fractions of the energy-weighted sum rules to be extracted. For bound collective states, the strengths for ${\pi }^{+}$ and ${\pi }^{\mathrm{-}}$ were nearly equal, as has been found for other scattering probes. Giant quadrupole and dipole excitations in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ (T=0) had nearly equal ${\pi }^{+}$ and ${\pi }^{\mathrm{-}}$ sum rule strengths. Quadrupole and monopole excitations in ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$ near 14 MeV show about twice the ${\pi }^{\mathrm{-}}$ transition strengths compared to those for ${\pi }^{+}$, contrary to expectations from simple isoscalar models.