Strong Interaction Studies via Meson-Nucleus Reactions

Abstract

The role of meson-nucleus reaction studies in the investigation of strong interactions is surveyed. In the first part, the pion-nucleus interaction in the region of the 3-3 resonance is discussed. Success and limitations of the Ll-h formalism which is based on the impulse approximation are examined. A consistent picture of a large variety of one-nucleon process­ es has been obtained and will be presented as well as failures in the basic understanding of two-body processes. In the second part, the various possibilities for specific strong inter­ action studies with particularly selected hadronic systems are demonstrated. The cases of K+ -nucleus interactions to examine quantitatively the basic impulse approximation, of K--nucleus resonance interactions for the study of orbitally excited baryons and the cases of S*- and 77'-nucleus interactions to investigate hadronic interactions in the presence of exotic multiquark or gluonic components are presented. Quarks and gluons constitute the microscopic degrees of freedom in strong interaction physics. Quarks are the constituents of hadronic matter, gluons are the carriers of the strong force. Nucleons and mesons constitute the effective degrees of freedom in terms of which nuclear structure and nuclear reactions are traditionally described. The relation between the microscopic and the effective degrees of free­ dom has not been established in nuclear physics. Neither is the success of the traditional description of nuclear phenomena properly understood, nor are its limita­ tions defined in precise terms. The central concept of the traditional description of nuclear reactions is that of the impulse-approximation. In the impulse approximation, the hadron-nucleus inter­ action is calculated in terms of the experimentally determined corresponding hadron­ nucleon interaction on the one hand and in principle well defined many .. body correc­ tions on the other. By construction, the impulse approximation becomes exact in the low density limit irrespective of the underlying hadron-nucleon dynamics. This is clearly one of the reasons for the success of such an approach in terms of effective degrees of freedom and phenomenological interactions. Within this framework, the microscopic degrees of freedom can show up only in the medium modification to the free hadron-nucleon interaction, i.e., only at the level where standard many-body corrections appear. To assess the validity of this effective description of nuclear reactions is possible only if this description has been carried through beyond the