Double Tag Events in Two-Photon Collisions at LEP

TL;DR

This paper reports measurements of double tag events in two-photon collisions at LEP energies, comparing experimental results with perturbative QCD predictions and BFKL calculations.

Contribution

It provides the first detailed measurement of the $ m{ extit{ extbf{ extgamma}}}^* m{ extit{ extbf{ extgamma}}}^*$ cross-section at LEP energies and tests QCD models against experimental data.

Findings

Results agree with perturbative QCD Monte Carlo predictions.

Quark Parton Model alone does not describe the data.

Measurements are consistent with NLO BFKL calculations.

Abstract

Double tag events in two photon collisions are studied using the L3 detector at the LEP center of mass energies $\sqrt{s} \simeq 189-202$ GeV. The cross-section of $\gamma ^* \gamma ^*$ collisions is measured at an average photon virtuality $<Q^2 > = 15 \rm{GeV}^2$. The results are in agreement with Monte Carlo predictions based on perturbative QCD, while the Quark Parton Model alone is insufficient to describe the data. The measurements are compared to the LO and the NLO BFKL calculations