Energy dependence of double giant resonances in pion double charge exchange

The energy dependence of the giant dipole resonance built on the isobaric analog state was measured in pion-induced double charge exchange on {sup 13}C at incident pion energies of 140-295 MeV. The cross-section increases with energy. The excitation function has a typical non-spin-flip signature, expected from simple considerations and verified by sequential model calculation. The results indicate that the pion DCX reaction excites this resonance predominantly via a two-step sequential process. Three narrower low-lying states in {sup 13}O (E{sub x}=2.9, 4.3 and 5.9 MeV) exhibit a clear spin=flip signature and most likely correspond to the giant Gamow-Teller strength built on the isobaric analog state. The authors will discuss the new results from LAMPF and the general features of these exotic nuclear states.