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

Abstract.

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.