Three-body correlations in electromagnetic dissociation of Borromean nuclei: The 6 He case

Dissociation of 6 He on a lead target has been studied at 240 MeV/u. The four-momenta of the two neutrons in coincidence with α -particles have been measured and used to reconstruct the three-body energy and angular correlations in the final state. For the first time, three-body correlations were included in the analysis of the 6 He dissociation data, and compared with calculations assuming a dipole mode for the electromagnetic dissociation. In addition, the experimental data have been analyzed using a series expansion of the final transition amplitude into hyperspherical functions, showing the importance of both nn and αn final-state interactions. It is shown that the dissociation process is governed by a transition of one neutron from the p -shell in the 6 He ground state to the s -shell in the continuum further indicating that the role of the transition through an intermediate 5 He( 3 / 2 − ) state is more important than expected.