Models of high energy ρρ,ρ̄ρ scattering

Abstract

A phenomenological description is sought of the dynamics operating in high energy elastic hadron-hadron scattering. The predictions of a simple Pomeron and weak cut model of high energy elastic scattering are compared with the new and surprising ρ̄ρ data from the ISR and Sρ̄ρS Collider. The model, which gives a complete account of all the lower energy data, is incompatible with the unexpected energy dependence of the differential cross-section shown by the Collider data. Modifications within the original framework of the model are examined but found inadequate and it is concluded that new contributions are necessary. Two avenues are explored as likely candidates for the correct approach. The first approach considered is the possible existence of a small odd charge conjugation term with constant or increasing contribution to the cross-section. Two existing models of such an "Odderon" effect are studied which give good agreement with the new data but neither of which are entirely satisfactory. A reggeized Odderon contribution, analagous to these models, is examined and limitations are placed on its effect. The second possibility considered as a description of the additional contributions to the model are the correction terms necessary to prevent the violation of unitarity and the breaking of asymptotic bounds. An eikonalization model, in which a-channel unitarity is explicitly satisfied, is reviewed but several theoretical problems emerge due to the nature of the basic exchange and the model gives a relatively poor description of the data. A" similar model in which the born term is described by a Pomeron with the appropriate Regge phase is developed. This clears up some of the theoretical problems but is found to exaggerate the problems encountered in fitting the data and it is concluded that such an eikonal description is unlikely to work. A simple model of the unitarity corrections which gives a better chance of reproducing the data is proposed. The results of the phenomenology of the asymptotic and perturbative Reggeon field theory approaches to elastic scattering are briefly reviewed.