# Measurements of the QED structure of the photon Academic Article

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• 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$$^2$$.