Measurement of the hadronic cross-section for the scattering of two virtual photons at LEP

Abstract.

The interaction of virtual photons is investigated using the reaction ${\rm e^+e^-} \rightarrow{\rm e^+e^-}$ hadrons based on data taken by the OPAL experiment at ${\rm e^+e^-}$ centre-of-mass energies $\sqrt{s_{\rm ee}}=189-209$ GeV, for $W>5$ GeV and at an average $Q^{2}$ of 17.9 GeV$^2$. The measured cross-sections are compared to predictions of the Quark Parton Model (QPM), to the Leading Order QCD Monte Carlo model PHOJET, to the NLO prediction for the reaction ${\rm e^+e^-}\rightarrow{\rm e^+e^-} q\bar{q}$, and to BFKL calculations. PHOJET, NLO ${\rm e^+e^-}\rightarrow{\rm e^+e^-} q\bar{q}$, and QPM describe the data reasonably well, whereas the cross-section predicted by a Leading Order BFKL calculation is too large.