Towards a complete description of high-energy photoproduction

Abstract

A real photon has a dual nature, as a pointlike elementary particle and as a qq uctuation, in the latter case often with hadron-like properties. Therefore high-energy p i n teractions 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 t w o distinct transverse momentum cut-o 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 di erent aspects of the photon. Predictions are presented for HERA events.

PYTHIA 6.4 physics and manual

“…Higher diffractive topologies, such as central diffraction, are currently neglected. In the following, the elastic and diffractive cross sections and event characteristics are described, as given in the model by Schuler and Sjöstrand [Sch94,Sch93a]. The non-diffractive component is identified with the 'minimum bias' physics already mentioned, a practical but not unambiguous choice.…”

“…In fact, the structure is still not so well understood. The model we outline is the one studied by Schuler and Sjöstrand [Sch93,Sch93a], and further updated in [Fri00]. In this model the physical photon is represented by…”

“…Historically, the model was first developed for photoproduction, i.e. a real photon on a hadron target [Sch93,Sch93a]. Thereafter γγ physics was added in the same spirit [Sch94a,Sch97].…”

“…X AB = X AB .) Parameterizations not provided in [Don92] have been calculated in the same spirit, making use of quark counting rules [Sch93a].…”

“…is resolved in a partonic substructure, then high-p ⊥ parton-parton interactions are possible, as described in sections 8.2.1 and 8.4.1. These interactions may be further subdivided into VMD and anomalous (GVMD) ones [Sch93,Sch93a]. 3.…”