Comment on the characterization of the giant quadrupole resonance inPb208as reported fromπ+/π−scattering

Studies of ${\pi }^{+}$/${\pi }^{\mathrm{-}}$ inelastic excitation of the giant quadrupole resonance in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ have been interpreted as implying a quadrupole matrix element ratio for neutron to proton excitations of $M_{\mathrm{n}/M_{\mathrm{p}=3.8\mathrm{}}}$, and a reduced electric transition rate of B(E2)↑=1010±600 $e^2$ ${\mathrm{fm}}^4$. These values are in strong disagreement with the results of a large body of inelastic light-ion scattering data as well as recent electron scattering results, all of which are consistent with a predominantly isoscalar character for this resonance. A similar situation prevails for the scattering of 400-MeV ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and 1428-MeV ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ ions where Coulomb excitation is important, and the inelastic cross sections are very sensitive to B(E2)↑ as well as the hadronic interaction strength. Studies of the photon decay of the giant quadrupole resonance are also in good agreement with random phase approximation calculations that imply a predominantly isoscalar character; this agreement would be destroyed if the interpretation of the pion experiment were correct.