Double giant dipole resonance in the (π-,π+) reaction

The double isovector giant dipole state has been observed in the (π-,π+)ΔTx=+2 double-charge-exchange reaction on 13C, 27Al, 40Ca, 56Fe, 59Co, and 93Nb. The resonances observed in the (π-,π+) reaction are closely related via Coulomb displacement energy and isospin symmetry to the resonances measured in the inverse (π+,π-) reaction on the same nuclei. The new observations provide a direct determination of the upper isospin component of the double giant dipole state, which is generally very weak in the (π+,π-) reaction. The comparison between the double dipole in the two double-charge-exchange modes gives valuable information on the isospin splitting and the Pauli-blocking effects for isotensor transitions