Probing the QCD pomeron in doubly tagged $e^+ e^-$ collisions

12 pp. (1999).
We calculate the total cross-section for $\gamma^* \gamma^*$ collisions and for the process $e^+ e^− → e^+ e^−$ +hadrons with two tagged leptons assuming dominance of the QCD pomeron exchange. We solve the BFKL equation including the dominant subleading effects generated by the consistency constraint which restricts the available phase-space of the emitted gluons to the region in which the virtuality of the exchanged gluons is dominated by their transverse momentum squared. Estimate of the possible soft pomeron contribution to the $\gamma^* \gamma^*$ cross-section is also presented. At very high CM energies W the calculated total $\gamma^* \gamma^*$ cross-section exhibits effective power-law $(W^2)^λ$ behaviour with $\lambda \tilde{} 0.3$. We confront our results with the recent measurements at LEP and give predictions for the energies which can be accessible at TESLA and at other future linear e + e − colliders.