Measurement of the low-x behaviour of the photon structure function \(F_2^\gamma\)

The photon structure function \(F_2^\gamma(x,Q^2)\) has been measured using data taken by the OPAL detector at \(\rm e^+e^-\) centre-of-mass energies of 91 GeV, 183 GeVand 189 \GeV, in \(Q^2\) ranges of 1.5–30.0 GeV\(^2\) (LEP1), and 7.0–30.0 GeV\(^2\) (LEP2), probing lower values of x than ever before. Since previous OPAL analyses, new Monte Carlo models and new methods, such as multi-variable unfolding, have been introduced, reducing significantly the model dependent systematic errors in the measurement. The results do not conclusively prove, but are completely consistent with, the presence of a rise in \(F_2^\gamma\) at low-x as expected from QCD.