Nuclear reactions: a tool to study halo nuclei
Pierre Capel (HIM, KPH Mainz)

The development of radioactive-ion beams (RIB) in the mid-80s has enabled the study of nuclear structure far from stability. Halo nuclei are probably the most peculiar feature uncovered through RIB. These light neutron-rich nuclei exhibit a much larger matter radius than their isobars.
This peculiarity is qualitatively explained by the very low separation of one or two neutrons observed in these nuclei. This low binding indeed enables the one or two valence neutrons to tunnel far away into the classically forbidden region and hence to exhibit a high probability of presence at a large distance from the other nucleons. Halo nuclei can thus be seen as a dense core surrounded by a neutron halo. These peculiar nuclei have been the focus of many theoretical and experimental studies.
Being radioactive, halo nuclei cannot be prepared as a target and studied through usual spectroscopic techniques. To infer information about their structure, one must resort to indirect techniques such as reactions. An accurate reaction model, coupled to a realistic description of the projectile is thus needed to extract reliable information from measurements. After an introduction on the physics of halo nuclei, I will describe the theoretical framework in which nuclear reactions are modelled. Then, I will present the state of the art in nuclear-reaction theory and the knowledge one can expect to gain from reaction data.