High precision studies of soft dipole mode in two-neutron halo nuclei: ${}^6$He case

The “soft dipole” E1 strength function is calculated for the transition from the ${}^6$He $0^{+}$ ground state to the $1^{-}$ continuum ${}^4$He+$n$+$n$. The calculations were performed within the hyperspherical harmonics formalism. The sensitivity of the results to the ${}^6$He ground state structure and to final state interactions, are analyzed. The large-basis calculations show the reliably converged results for soft dipole strength function and for momentum correlations of the ${}^{6}He\to {}^4$He+$n$+$n$ dissociation products. Transition mechanisms are analyzed based on the momentum correlations. The comparison with experimental data is provided.