Non-linear QCD dynamics in two-photon interactions at high energies

TL;DR

This paper investigates high-energy two-photon interactions within the Color Glass Condensate framework, using the BK equation to predict observables for future colliders and comparing models with existing data.

Contribution

It introduces a new relation between dipole-dipole cross section and scattering amplitude, applying the BK equation with running coupling to predict high-energy photon interactions.

Findings

Models fit LEP data at high energies

Predictions diverge at higher energies for different models

Study can constrain QCD dynamics at future colliders

Abstract

Perturbative QCD predicts that the growth of the gluon density at high energies should saturate, forming a Color Glass Condensate (CGC), which is described in mean field approximation by the Balitsky-Kovchegov (BK) equation. In this paper we study the $\gamma \gamma$ interactions at high energies and estimate the main observables which will be probed at future linear colliders using the color dipole picture. We discuss in detail the dipole - dipole cross section and propose a new relation between this quantity and the dipole scattering amplitude. The total $\gamma \gamma$, $\gamma^{*} \gamma^{*}$ cross-sections and the real photon structure function $F_2^{\gamma}(x,Q^2)$ are calculated using the recent solution of the BK equation with running coupling constant and the predictions are compared with those obtained using phenomenological models for the dipole-dipole cross section and scattering amplitude. We demonstrate that these models are able to describe the LEP data at high energies, but predict a very different behavior for the observables at higher energies. Therefore we conclude that the study of $\gamma \gamma$ interactions can be useful to constrain the QCD dynamics.