Continuum spectroscopy of halo nuclei

Halo nuclei represent a new type of structure found in extremely neutron rich light nuclei, at the limits of nuclear existence. Of particular interest are Borromean nuclei, where none of the binary substructures can bind. Similar structures, Efimov states, have now also been produced in traps in molecular physics. Nuclear physics has in recent years taken further steps to also explore the nature of the halo continuum, in fact the major part of the spectrum since halo nuclei support only one or a few bound states. Since 3 → 3 scattering is prohibitively difficult to perform, the halo continuum has so far been excited in binary collisions, proceeding via the exotic ground state which to various degrees puts its imprint on the result. Below we discuss via examples how to disentangle continuum structures, comparing with recent correlation data. The work involves a consistent treatment of halo structure and reaction theory, and emphasizes the important future role of exclusive observables and complete experiments. (author)