Towards a complete description of high-energy photoproduction

A real photon has a dual nature, as a pointlike elementary particle and as a qq fluctuation, in the latter case often with hadron-like properties. Therefore high-energy γp interactions have a rich and not yet well explored structure. In this paper, we propose a consistent formulation, which is based on a subdivision of the total cross section into three distinct event classes: direct, VMD and anomalous. The VMD class, in its turn, contains the subclasses familiar from hadron-hadron 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 remnant structures. A major rôle is played by two distinct transverse momentum cut-off scales, which separate the classes. When all the ingredients are put together, we obtain a detailed model for photoproduction events. In order to test this approach, we also propose several alternative scenarios, each of which emphasizes different aspects of the photon. Predictions are presented for HERA events.