Abstract
The momentum distributions of the residual nuclei after one-neutron removal, measured in coincidence with gamma rays, identify the excited levels of these residues. The resulting differential partial cross sections map the momentum content and structure of the removed-nucleon wave function and provide an exacting test of theory. Data for population of the C-14 and Be-10 ground states show an asymmetry that is incompatible with the currently used eikonal descriptions. A fully dynamical description of the elastic break-up mechanism provides an understanding of the new observation, which will be most pronounced for nuclear halo states, This interpretation is clarified by an analysis of the angular distribution of the heavy residues.