FINGERPRINTS OF A POSSIBLE LOW-LYING RESONANCE IN LI-11

Radioactive beams of Borromean halo-like nuclei like Li-11 have provid ed possibilities for studying the exotic structure of such objects. Si nce the information is obtained in collision studies, in particular fr om break-up channels, one has to disentangle the structure information from the reaction mechanism. A satisfactory treatment within a three- body model for the projectile requires a four-body continuum calculati on. As an exploratory step towards this end, we give a phenomenologica l discussion based on data for He-6 and Li-11 projectiles for high and low energies from 1 GeV A(-1) down to 30 MeV A(-1). Data for both tra nsverse and longitudinal momentum distributions for the three-body con stituents of these projectiles are used. We argue that the data can be consistently understood in a picture where the high-energy data mainl y correspond to direct break-up of the projectile ground state in a Se rber model, while the low-energy data exhibit the fingerprint of a seq uential break-up process via a narrow low-lying resonance, observed in He-6 but hitherto not identified in Li-11.