Comparison of the double giant-dipole states observed in (π−,π+) and (π+,π−) reactions onCa40andAl27

The double isovector giant-dipolar state has been observed in the (${\mathrm{\pi }}^{\mathrm{-}}$,${\mathrm{\pi }}^{+}$) Δ${\mathit{T}}_{\mathit{z}}$=+2 and (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{\mathrm{-}}$) Δ${\mathit{T}}_{\mathit{z}}$=-2 double-charge-exchange reactions on ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$. The resonances observed in the (${\mathrm{\pi }}^{\mathrm{-}}$,${\mathrm{\pi }}^{+}$) reaction are closely related via Coulomb energy and isospin symmetry to the resonances measured in the inverse (${\mathrm{\pi }}^{+}$,${\mathrm{\pi }}^{\mathrm{-}}$) reaction on the same nuclei. The new observations provide strong support for the identification of the double giant-dipole state in nuclei. The differences between the self-conjugate and non-self-conjugate cases are outlined.