Excitation of the Isoscalar Giant Quadrupole Resonance inSn118(π±,π±′)

Ths isoscalar giant quadrupole resonance is studied in ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}({\pi }^{\pm },{\pi }^{\pm \prime })$ at 130 MeV. It is found that the ratio of ${\pi }^{-}$ to ${\pi }^{+}$ cross sections at their maximum is 1.9 and that 57% of the energy-weighted sum rule is exhausted in ${\pi }^{-}$ scattering. This large ratio of ${\pi }^{-}$ to ${\pi }^{+}$ cross sections is not anticipated by conventional models, and may be interpreted as evidence for substantial isovector strength.