Survey of present data on photon structure functions and resolved photon processes

Present data on the partonic content of the photon from LEP, TRISTAN and HERA accelerators are reviewed and the essential aspects of the underlying ideas and methods are pointed out. Results of the unpolarized photon structure function F2γ from DISeγ experiments and on large pT jet production processes in the resolved γγ collisions are presented for both real and virtual photons. The results of analysis of the hadronic final state accompanying the DISeγ measurements, showing some discrepancies with the Monte Carlo models, are collected together and presented as a separate issue. Also results on the DISeγ with leptonic final states are shown. The results from resolved real and virtual photon processes at HERA collider based on the single- and double-jet events, also charged particles and prompt photons, are presented. In the context of virtual photon processes the data for forward jet and forward particle production are included. In addition, a short presentation of the recent data on the heavy quark content of the photon is given. Related topics – the polarized (spin-dependent) structure functions for the real and virtual photon, the structure function of the electron and the photonic content of the proton are also shortly mentioned.