Measurements of the QED structure of the photon Academic Article uri icon


  • The structure of both quasi-real and highly virtual photons is investigated using the reaction \({\rm e^+e^-}\rightarrow{\rm e^+e^-}\mu^+\mu^-\), proceeding via the exchange of two photons. The results are based on the complete OPAL dataset taken at \({\rm e^+e^-}\) centre-of-mass energies close to the mass of the Z boson. The QED structure function \(F^\gamma _2\) and the differential cross-section \({\rm d}\sigma/{\rm d}x\) for quasi-real photons are obtained as functions of the fractional momentum x from the muon momentum which is carried by the struck muon in the quasi-real photon for values of \(Q^2\) ranging from 1.5 to 400 GeV\(^2\). The differential cross-section \({\rm d}\sigma/{\rm d}x\) for highly virtual photons is measured for \(1.5 P^2\). Based on azimuthal correlations the QED structure functions \(F^\gamma _{\rm A}\) and \(F^\gamma _{\rm B}\) for quasi-real photons are determined for an average \(Q^2\) of 5.4 GeV\(^2\).


publication date

  • January 1, 1999