Do halo nuclei follow Rutherford Elastic Scattering at energies below the barrier? The case of [superscript 11]Li

Abstract

The first measurement of the elastic scattering of the halo nucleus [superscript 11]Li and its core [superscript 9]Li on [superscript 208]Pb at energies near the Coulomb barrier is presented. The [superscript 11]Li + [superscript 208]Pb 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 [superscript 11]Li + [superscript 208]Pb is the consequence of the halo structure of [superscript 11]Li, as it is not observed in the elastic scattering of its core [superscript 9]Li at the same energies. Four-body continuum-discretized coupled-channels calculations, based on a three-body model of the [superscript 11]Li 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 [superscript 11]Li. These calculations suggest the presence of a low-lying dipole resonance in [superscript 11]Li close to the breakup threshold.