Topics in the generalized vector dominance model

Abstract

This thesis covers two topics in the Generalized Vector Dominance Model. In the first topic we construct a model for dilepton production in hadron·hadron interactions based on the idea of generalized vectordominance. We argue that in the high-mass region the generalized vectordominance model and the Drell-Yan parton model are alternative descriptions of the same underlying physics. In the low-mass regions the models differ; the vector-dominance approach predicts a greater production of dileptons. We compare the model to the limited dilepton data that are presently available and also integrate over one of the leptons to study the contributions to the single-lepton yield. Without the benefit of some very recent data we find that the high-mass vector mesons which are the hallmark of the generalized vector-dominance model make little contribution to the large yield of leptons observed in the transverse-momentum range 1 < p .< 6 GeV. The recently measured hadronic parameters lead one to believe that detailed fits to the data are possible under our model. The possibility was expected, and we illustrate with a simple model the extreme sensitivity of the large-p lepton yield to the 1arge- transverse-momentum tail of vector-meson production. The second topic is an attempt to explain the mysterious phenomenon of photon shadowing in nuclei utilizing the contribution of the 10ngitudinally polarized photon. We argue that if the scalar photon antishadows, it could compensate for the transverse photon, which is presumed to shadow. We find in a very simple model that the scalar photon could indeed anti-shadow. The principle feature of our model is a cancellation of amplitudes. The scheme is consistent with scalar photonnucleon data as well. We test our idea with two simple GVDM models and find that the anti-shadowing contribution of the scalar photon is not sufficient to compensate for the contribution of the transverse photon. We find it doubtful that the scalar photon makes a significant contribution to the total photon-nuclear cross section.