TOWARDS A COMPLETE DESCRIPTION OF HIGH-ENERGY PHOTOPRODUCTION

A real photon has a dual nature, as a pointlike elementary particle an d as a qqBAR fluctuation, in the latter case often with hadron-like pr operties. Therefore high-energy gammap interactions have a rich and no t yet well explored structure. In this paper, we propose a consistent formulation, which is based on a subdivision of the total cross sectio n into three distinct event classes: direct, VMD and anomalous. The VM D class, in its turn, contains the subclasses familiar from hadron-had ron physics. Within this approach, we calculate all the partial cross sections. Many other aspects of the event classes are also considered, such as proton and photon structure functions, jet rates and beam rem nant structures. A major role is played by two distinct transverse mom entum cut-off scales, which separate the classes. When all the ingredi ents are put together, we obtain a detailed model for photoproduction events. In order to test this approach, we also propose several altern ative scenarios, each of which emphasizes different aspects of the pho ton. Predictions are presented for HERA events.