We discuss several mechanisms of heavy quark production in (real) photon-nucleon and (real) photon (real) photon collisions. In particular we focuse on application of the Saturation Model. We discuss how to generalize the formula from virtual photon proton scattering and analyze threshold effects. We discuss a possibility to measure the cross section for γγ → 2c2c̄. In addition to the main dipol...

A preliminary update of the previous OPAL measurement of the inclusive production of D mesons in anti-tagged photon-photon collisions is presented together with the first preliminary OPAL measurement of bottom production in photon-photon collisions.

Photon-photon collisions are investigated in the framework of the two-component Dual Parton Model. The model contains contributions from direct, resolved soft and resolved hard interactions. All free parameters of the model are determined in fits to hadronhadron and photon-hadron cross section data. The model is shown to agree well to hadron production data from hadron-hadron and photon-hadron ...

I discuss mechanisms of heavy quark production in (real) photon-nucleon and (real) photon (real) photon collisions. In particular, I focuse on application of the Saturation Model. In addition to the main dipole-nucleon or dipole-dipole contribution included in recent analyses, I propose how to calculate within the same formalism the hadronic single-resolved contribution to heavy quark productio...

This review covers selected results from the LEP experiments on the structure of quasi-real and virtual photons. The topics discussed are the total hadronic cross-section for photon-photon scattering, hadron production, jet cross-sections, heavy quark production for photon-photon scattering, photon structure functions, and crosssections for the exchange of two virtual photons.