2 n -transfer contribution in the 4 H e ( 6 H e , 6 H e ) 4 He cross section at E c . m . = 11.6 MeV

The ${}^{6}\mathrm{He}$ $+$ ${}^{4}\mathrm{He}$ elastic scattering cross section was measured at ${E}_{\mathrm{c}.\mathrm{m}.}=11.6\mathrm{MeV}$ using a ${}^{6}\mathrm{He}$ radioactive beam and a ${}^{4}\mathrm{He}$-implanted Al foil as target. The use of the thin implanted target allowed to enlarge the angular range in which the data were collected, with respect to a previous measurement at the same center-of-mass energy. The new and previous data are compared with several calculations. The inclusion of a description for the $2n$-transfer process, either with a parity-dependent term, or with a distorted-wave Born approximation transfer amplitude, is crucial to reproduce the increase of the cross section at large angles, thus assessing the contribution of the $2n$-transfer process to the reaction. At the present energy, the complicated nature of the transfer process and the possible role played by the coupling to other channels, in particular, the breakup, require sophisticated reaction models in order to extract the relevant information on the peculiar ${}^{6}\mathrm{He}$ nucleus. The quality of the data is such that the differences between ${}^{6}\mathrm{He}$ and the similar ${}^{6}\mathrm{Li}$ system should be identified by such calculations.