2018 Impact factor 4.843
Particles and Fields
Eur. Phys. J. C 11, 409-425
DOI 10.1007/s100529900205

Measurements of the QED structure of the photon

The OPAL Collaboration

G.Abbiendi$^{\rm 2}$ - et al.

2 Dipartimento di Fisica dell' Università di Bologna and INFN, 40126 Bologna, Italy

Received: 8 February 1999 / Published online: 28 September 1999

Abstract
The structure of both quasi-real and highly virtual photons is investigated using the reaction $\ensuremath{\rm e^+e^-}\rightarrow\ensuremath{\rm e^+e^-}\ensuremath{\mu^+\mu^-} $, proceeding via the exchange of two photons. The results are based on the complete OPAL dataset taken at \ensuremath{\rm e^+e^-}centre-of-mass energies close to the mass of the \ensuremath{\rm Z}boson. The QED structure function \ensuremath{F_{\mathrm{2}}^{\gamma}}and the differential cross-section \ensuremath{\mathrm{d}\sigma/\mathrm{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 \ensuremath{Q^{2}}ranging from 1.5 to 400 \ensuremath{\rm GeV^2}. The differential cross-section \ensuremath{\mathrm{d}\sigma/\mathrm{d}x}for highly virtual photons is measured for $1.5< \ensuremath{Q^{2}} < 30$ \ensuremath{\rm GeV^2}and $1.5< \ensuremath{P^{2}} < 20$ \ensuremath{\rm GeV^2}, where \ensuremath{Q^{2}}and \ensuremath{P^{2}}are the negative values of the four-momentum squared of the two photons such that $\ensuremath{Q^{2}} >\ensuremath{P^{2}} $. Based on azimuthal correlations the QED structure functions \ensuremath{F_{\mathrm{A}}^{\gamma}}and \ensuremath{F_{\mathrm{B}}^{\gamma}} for quasi-real photons are determined for an average \ensuremath{Q^{2}}of 5.4 \ensuremath{\rm GeV^2}.


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