In two-neutron halo nuclei, the importance of two-neutron correlation in their binding mechanisms has been suggested from the core+n+n three-body calculations. This two-neutron correlation is characterized as the spatially-localized n-n pair, the so-called dineutron, and has attracted much attention from both theoretical and experimental sides.
In this talk, we discuss the dineutron correlations in the ground and excited states of two-neutron halo nuclei by using two kinds of reactions.
For the excited states, we consider the nuclear breakup reaction of 6He. We investigate the decay mode of the 2+ resonant state, which is populated by the breakup reaction by 12C at 240 MeV/nucleon, and discuss the role of two-neutron correlation in decay from the 2+ resonance.
For the ground state, we investigate the neutron knockout reaction of 6He. In quasifree knockout reactions, the knocked-out neutron is free from final-state interactions, and it is expected that we could extract the ground-state information from the observables. We discuss the possibility of direct measurement of dineutron correlation in the knockout reaction.