γγ Physics

Abstract

This chapter is devoted to QCD and, more generally, Strong Interaction studies in γγ collisions. For our purposes, LEP2 is a continous energy γγ collider with a reach of up to 100 GeV center of mass energy for some observables. At low energy, the main studies concern resonance production and quasi two-body processes which probe the meson and baryon wavefunctions. At high energy, the partonic structure of the photon plays a dominant role and, as for hadronic processes, several tests of perturbative QCD, using many different observables, are possible. A specific feature of γγ collisions is the variability of the mass of the incoming photons which can be used to tune the non-perturbative component of the photon.