Proton elastic scattering with ⁹Li and ¹¹Li and its halo structure

We have studied the proton elastic scattering of ⁹Li and ¹¹Li using the Born approximation and the optical potential approach. We first studied the data qualitatively by the Born approximation and found that the small cross section of p + ¹¹Li, which had been observed at E_p = 62 MeV, can be understood as the break-up effect of halo neutrons from ¹¹Li. We then searched for the optical potential parameters for both p + ⁹Li and p + ¹¹Li under the assumption that ¹¹Li has a halo structure of two weakly bound neutrons around the ⁹Li core. We found a good parameter set and concluded that the break-up effect of halo neutrons is essential to understand the p + ¹¹Li data.