Measurement of the Hadronic Photon Structure Function F_2^gamma at LEP2

TL;DR

This paper reports on measurements of the photon structure function F_2^gamma at LEP2, showing QCD-predicted positive scaling violations and comparing various theoretical parameterisations with experimental data.

Contribution

First measurement of F_2^gamma at high Q^2 extending previous OPAL results, testing QCD predictions and comparing with models.

Findings

F_2^gamma increases with Q^2, confirming positive scaling violations.

Several parameterisations match the data, but the quark-parton model does not.

Data extends previous measurements to higher Q^2 values.

Abstract

The hadronic structure function of the photon F_2^gamma is measured as a function of Bjorken x and of the factorisation scale Q^2 using data taken by the OPAL detector at LEP. Previous OPAL measurements of the x dependence of F_2^gamma are extended to an average Q^2 of 767 GeV^2. The Q^2 evolution of F_2^gamma is studied for average Q^2 between 11.9 and 1051 GeV^2. As predicted by QCD, the data show positive scaling violations in F_2^gamma. Several parameterisations of F_2^gamma are in agreement with the measurements whereas the quark-parton model prediction fails to describe the data.