Soft dipole resonance in neutron-rich 8He

Abstract In neutron-rich 8He, we study the soft dipole resonance, which is regarded as a oscillation of four valence neutrons against 4He core, and its effect on low-energy electric strength with 4He+n+n+n+n five-body cluster model. This work an extended earlier letter [T. Myo K. Kat?, Phys. Rev. C 106, L021302 (2022)]. The unbound 1? states 8He are obtained complex-energy eigenvalues by using complex scaling method calculated in terms complex-scaled Green’s function. Two kinds dominant excitation modes confirmed below 20 MeV energy. strengths 10 exhausted 7He+n channel, sequentially decays to 6He+n+n. Above MeV, arise from mode (4n) oscillating core. We further explore possibility resonance for this state carefully searching pole finally predict corresponding energy 14 decay width 21 MeV. exhausts about half relative motion between core 4n.