Single-neutron removal reactions from ¹⁵C and ¹¹Be: Deviations from the eikonal approximation

The momentum distributions of the residual nuclei after one-neutron removal have been measured in coincidence with gamma rays identifying the distributions associated with the excited and ground state levels of these residues. These differential partial cross sections map the momentum content of the removed-nucleon wave functions and their description provides an exacting test of the reaction dynamics. Momentum distribution data when populating the ¹⁴C and ¹⁰Be ground states show a low-high momentum asymmetry that is incompatible with the hitherto used eikonal descriptions. A fully dynamical coupled discretized continuum channels description of the elastic breakup mechanism is shown to provide an understanding of this new observation which is most pronounced for weakly bound, s-wave, nuclear halo states. This interpretation is clarified further by an analysis of the momentum distributions as a function of the angle of detection of the heavy ground state residues.