Measurements of the QED Structure of the Photon

TL;DR

This paper measures the QED structure functions of photons using e+e- collision data, providing detailed insights into the photon structure across various virtuality ranges and confirming QED predictions.

Contribution

It presents the first comprehensive measurements of the QED structure functions of both quasi-real and highly virtual photons using the OPAL dataset.

Findings

Measured F_2^gamma and dsigdx for quasi-real photons across a wide Q^2 range.

Determined F_A^gamma and F_B^gamma structure functions for quasi-real photons.

Provided data consistent with QED predictions for photon structure functions.

Abstract

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 dsigdx 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 dsigdx 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.