Elastic scattering of $^{8}$He + $^{4}$He and two-neutron transfer and the influence of resonances in $^{12}$Be

Scattering of $^8$He from $^4$He has been performed through the coincident detection of the scattered particles using a silicon array within a helium-4 gas volume with a $^8$He beam. This permitted the reconstruction of the interaction probability as a function of position within the gas and hence the excitation function to be calculated together with the angular distribution of the products. These measurements also enabled the reconstruction of the two-neutron transfer to $^6$He + $^6$He. The measurements provide the first characterisation of the scattering of the α+4n , $^8$He, halo nucleus from $^4$He and the 2n-transfer to populate the symmetric final state. The results indicate the presence of a L=4 component at excitation energies of 14–15 MeV, consistent with a broad ( ∼1 MeV ) $J^π$=4$^+$ resonance. These measurements would agree with generalized two-centre cluster model (GTCM) calculations indicating a cluster, or molecular, structure predicted at this energy.