Two-neutron transfer in nuclei close to the drip line

Abstract

We investigate the two-neutron transfer modes induced by $(t,p)$ reactions in neutron-rich oxygen isotopes. The nuclear response to the pair transfer is calculated in the framework of continuum quasiparticle random phase approximation (cQRPA). The cQRPA allows a consistent determination of the residual interaction and an exact treatment of the continuum coupling. The $(t,p)$ cross sections are calculated within the distorted wave Born approximation approach and the form factors are evaluated by different methods: macroscopically, following the Bayman and Kallio method, and fully microscopically. A significant part of the cross section corresponds to a high-lying collective mode built entirely upon continuum quasiparticle states.