Possible existence of a low-energy octupole resonance in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$

The possibility of a low-energy octupole resonance in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ which exhausts a significant fraction of the energy-weighted isoscalar sum rule is investigated in a distorted-wave-Born-approximation–random-phase-approximation model. It is found that the ∼15% sum-rule fraction, seen recently in low-energy (p,p’) reactions, depends sensitively on the strength of the isovector projectile-target nucleon interaction.