Measurements of the QED structure of the photon

The structure of both quasi-real and highly virtual photons is investigated using the reaction e(+)e(-) --> e(+)e(-) mu(+)mu(-), proceeding via the exchange of two photons. The results are based on the complete OPAL dataset taken at e(+)e(-) centre-of-mass energies close to the mass of the Z boson. The QED structure function F(2)(gamma) and the differential cross-section d sigma/dx 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 d sigma/dx for highly virtual photons is measured for 1.5 < Q(2) < 30 GeV(2) and 1.5 < P(2) < 20 GeV(2), where Q(2) and P(2) are the negative values of the four-momentum squared of the two photons such that Q(2) > P(2). Based on azimuthal correlations the QED structure functions F(A)(gamma) and F(B)(gamma) for quasi-real photons are determined for an average Q(2) of 5.4 GeV(2).