One-neutron knockout from individual single-particle states of Be-11

The structure of the halo nucleus Be-11 has been studied using the reaction Be-9(Be-11,Be-10 + gamma) at 60 MeV/nucleon. The ground State structure of Be-11 is determined by comparing the experimental cross sections to a calc ulation combining spectroscopic factors from the shell model with l-depende nt single-particle cross sections obtained in an eikonal model. This experi ment shows the dominant 1s single-particle character of the Be-11 ground st ate and indicates a small contribution of 0d admixture in the wave function . After correction for the approximately 22% intensity to excited levels,a clean and precise distribution of parallel momentum for knockout from the 1 s halo wave function is obtained for the first time.