R-Matrix Analysis

Abstract

Experiments involving polarization techniques have nowhere unearthed a richer structure of observed phenomena than in those scattering and reaction processes involving very few nucleons. This paper is concerned with a program, carried out with colleagues at Los Alamos, with its first goal as a phenomenological understanding of these processes. It is the belief of those of us working on this program that our approach is essentially dictated by the fact that the overwhelming amount of information already collected seems to be still only marginally sufficient to describe the complex behavior of these systems. This somewhat paradoxical situation, that an almost unmanageable quantity of data is still perhaps just on the threshold of encompassing all aspects of the behavior of such a system, seems to call for an approach with two main features. First, all channels and all complementary experiments should be described simultaneously. Second, an energy dependent parameterization should be used, if only because the data are not sufficiently complete at single energies. The simultaneous description of all channels allows us to make use of the very important principle of unitarity of the collision matrix S. The need for an energy dependent parameterization has led us to choose the R-matrix formalism. In this context that formalism is to be regarded as a practical tool. This paper does not discuss the role of the R-matrix in general theories of nuclear reactions. It may be, however, that the results of the present work will have a place in such discussions.