Measurement of the Hadronic Photon Structure Function in Two-Photon Collisions

The photon is surely one of the most important elementary particles, and consequently its interaction and structure is of extraordinary interest. In the classical theory of light there is no interaction between light waves, even the photon as a particle does not exist. But quantum field theory allows that photons fluctuate into pairs of charged particles over a short period of time due to the Heisenberg uncertainty principle and in this way can interact with each other. e + e −colliders like LEP at CERN provide an experimental environment in which high energy photons are produced with sufficient luminosity so that interesting two-photon experiments can be performed.