Do Halo Nuclei Follow Rutherford Elastic Scattering at Energies Below the Barrier? The Case of 11Li

The first measurement of the elastic scattering of the halo nucleus Li-11 and its core Li-9 on Pb-208 at energies near the Coulomb barrier is presented. The Li-11 + Pb-208 elastic scattering shows a strong reduction with respect to the Rutherford cross section, even at energies well below the barrier and down to very small scattering angles. This drastic change of the elastic differential cross section observed in Li-11 + Pb-208 is the consequence of the halo structure of Li-11, as it is not observed in the elastic scattering of its core Li-9 at the same energies. Four-body continuum-discretized coupled-channels calculations, based on a three-body model of the Li-11 projectile, are found to explain the measured angular distributions and confirm that the observed reduction is mainly due to the strong Coulomb coupling to the dipole states in the low-lying continuum of Li-11. These calculations suggest the presence of a low-lying dipole resonance in Li-11 close to the breakup threshold. DOI: 10.1103/PhysRevLett.109.262701