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

The weakly-bound 8He nucleus exhibits a neutron halo or thick neutron skin and is generally considered to have an α+4n structure in its ground state, with the four valence neutrons each occupying 1p3/2 states outside the α core. The 8He(p,t)6He reaction is a sensitive probe of the ground state structure of 8He, and we present a consistent analysis of new and existing data for this reaction at incident energies of 15.7 and 61.3AMeV, respectively. Our results are incompatible with the usual assumption of a pure (1p3/2)4 structure and suggest that other configurations such as (1p3/2)2(1p1/2)2 may be present with significant probability in the ground state wave function of 8He.