Rearrangements in three-body decaying resonances

Abstract

Three-body decays of many-body nuclear resonances are processes where N particles in a quasi-stable configuration are divided into three fragments. The momentum distributions of the fragments carry the information of the resonance and the decay process. Calculated results should be compared to accurate and complete measurements with the purpose of extracting such information. Two almost independent problems must be solved before fully reliable results become available. First, contraction of the N-body degrees of freedom to those of three particles has to be consistently achieved. This presents a conceptual problem since it implies matching of rather incompatible models and the related effective interactions. The second problem is that the resonance structure often furthermore undergoes major changes from small to large distances. The couplings causing these changes may in principle be known within a given three-body model, but even under this assumption, the accuracy requirements are very hard to meet in difficult cases. Different reasons apply to different cases. One example is when very small couplings extend over large distances as for prominent substructures. We illustrate these two open problems with a number of nuclear three-body decays. We emphasize that these problems are the simplest of a much more advanced series of multi-body decays and reaction processes proceeding from N particles to three-body clusters.