Soft Dipole Resonances in 8 He and 8 C

Soft dipole resonances in 8 He and 8 C are investigated by applying the complex scaling method to the α + N + N + N + N five-body model for the isospin T = 2 system. The 1 − excited resonant states are calculated at ( E x , Γ) = (14.0, 21.1) MeV and (12.7, 24.0) MeV for 8 He and 8 C, respectively. From the analyses of the configuration mixing and the spatial properties, the soft dipole resonances of two nuclei are understood to be the vibrational states of valence nucleons and the α core. They are also seen to have a good isospin symmetry. In contrast, the ground states of two nuclei show different spatial properties indicating the symmetry breaking due to the Coulomb repulsion of valence protons in 8 6 C 2 .