Two-neutron halo state of 15B around 3.48 MeV by a three-body model

We investigate low-lying bound states of the neutron-rich nucleus 15B by assuming it is a three-body system made of an inert core 13B and two valence neutrons. The three-body wave functions are obtained using the Faddeev formalism. Special attention is paid to the excited state at 3.48(6) MeV observed in the 13C(14C,12N)15B reaction, whose properties are less clear theoretically. In our three-body model, besides the ground state , a second state is discovered at around 3.61 MeV, which might be identified with the excited state observed at 3.48(6) MeV. We study this state in detail. It turns out to be a two-neutron halo state with a large matter radius .