Introduction

Nuclear halo states are one of the more fascinating phenomena discovered in the spectrum of light nuclei. They occur close to the neutron drip lines as a threshold phenomenon when one or more weakly bound nucleons tunnel into the surrounding space. The general structure of these halo states is by now almost generally understood, but the precise role of intruder states and pairing in the continuum still needs to be discussed theoretically and experimentally. The existence of halo states has important consequences for the continuum spectra of such nuclei. This continuum can be probed in low-energy reactions important in astrophysics, or in breakup reactions of halo projectiles. A great deal more work is needed to understand the many-body continuum of two-nucleon halo systems. Here, it will be instructive to examine the isospin analogue, namely two-proton radioactivity in nuclei in the vicinity of the proton dripline. Possible proton halo states are also under discussion now.

Experimental probing of halo states continues to be obtained from more precise breakup and particle transfer reactions, and supplements the measurements of size, of momentum distributions of fragments, and of beta decays to or from halo states. Most recently, the kinematically-complete measurements of breakup reactions is leading to a new experimental wealth of information on structures in the continuum of halo nuclei, including Borromean continuum. Details of two-neutron correlations and core-excited states have been measured, challenging both halo structure models and theories of reaction dynamics.

It is therefore necessary to combine present and future theoretical capabilities with detailed and accurately-specified experimental observations. The aim of the planned workshop is therefore to gather theorists, and experimentalists with a flair for theory, to take the measure of current and future progress in this field.

This workshop is a natural followup of the previous workshops help in 1996 and 2001 with the same title and the same organisers. These were judged by both the theory and experimental participants to provide most instructive, fruitful and informal meeting grounds for the detailed discussion of all the necessary issues. Since we see that much has developed in the five years since the last meeting, a successor workshop should prove similarly beneficial.