Probing the 8 He ground state via the 8 He(p,t) 6 He reaction

The weakly-bound 8 He nucleus exhibits a neutron halo or thick neutron skin and is generally considered to have an � + 4n structure in its ground state, with the four valence neutrons each occupying 1p 3/2 states outside thecore. The 8 He(p,t) 6 He reaction is a sensitive probe of the ground state structure of 8 He, and we present a consistent analysis of new and existing data for this reaction at incident energies of 15.7 and 61.3 A MeV, respectively. Our results are incompatible with the usual assumption of a pure (1p3/2) 4 structure and suggest that other configurations such as (1p 3/2 ) 2 (1p 1/2 ) 2 may be present with significant probability in the ground state wave function of 8 He.