Pion inelastic scattering to giant resonances and low-lying collective states in 118Sn and 40Ca.

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 \ensuremath{\beta}R and fractions of the energy-weighted sum rules to be extracted. For bound collective states, the strengths for ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ 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 ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ sum rule strengths. Quadrupole and monopole excitations in $^{118}\mathrm{Sn}$ near 14 MeV show about twice the ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ transition strengths compared to those for ${\ensuremath{\pi}}^{+}$, contrary to expectations from simple isoscalar models.