Measurements of the QED structure of the photon

The OPAL Collaboration: G. Abbiendi - et al.

doi:doi:10.1007/s100529900205

2022 Impact factor 4.4

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 $\ensuremath{\rm GeV^2}$ .