Anomalous population of 10He states in reactions with 11Li

Structure with the lowest energy observed in the He-10 spectrum populated in the proton knockout reaction with a Li-11 beam has a peak at 1.2 to 1.5 MeV. This peak is usually interpreted as a resonant 0(+) ground state of He-10. Our theoretical calculations indicate that this peak is likely to be a superposition of 1(-), 0(+), and 2(+) excitations with very similar shapes. Moreover, the soft 1(-) excitation appears to be the lowest in energy. Such an anomalous continuum response is traced to the halo structure of Li-11 providing an extreme low energy shift to all the expected continuum excitations. Competition between effects on the spectrum of the initial-state structure and of the final-state interaction and three-body correlations in He-10 are discussed. The analogous effect of an extreme low-energy shift could also be expected in other cases of 2n emitters populated in reactions with halo nuclei. A simplified example of the He-10 spectrum in alpha knockout from Be-14 is given. We also discuss limits on the properties of He-9 stemming from the observed He-10 spectrum.