Giant dipole resonances built on isobaric analog states in pion double charge exchange

Giant resonances were observed in (+,-) double charge exchange (at T=292 MeV) on Fe56, Se80, and Pb208 at excitation energies of 28.5, 34.6, and 43.6 MeV, respectively. An angular distribution for Fe56 was measured and observed to have a dipole shape. The variation of excitation energy above the double isobaric analog state is consistent with an A-1/3 dependence, as expected for giant dipole resonances built on the isobaric analog states. The Fe56 angular distribution agrees well with a coupled-channels impulse-approximation calculation in which sequential single charge exchange through the isobaric analog to the giant dipole resonance is evaluated.