Tracking fast small color dipoles through strong gluon fields at the LHC

TL;DR

This paper proposes using high-energy gamma + nucleus collisions at the LHC to investigate a new perturbative QCD regime involving small dipoles interacting strongly with nuclear matter, enabling insights into gluon saturation effects.

Contribution

It introduces a novel experimental approach to probe small dipole interactions at high energies, expanding understanding of QCD in the strong absorption regime.

Findings

First heavy ion run at LHC can study the reaction with sufficient statistics.

Probes qar q dipoles of size ~0.2 fm at x ~ 10^{-5}.

Potential to test onset of a new perturbative QCD regime.

Abstract

We argue that the process gamma +A \to J/psi + gap + X at large momentum transfer provides a quick and effective way to test onset of a novel perturbative QCD regime of strong absorption for the interaction of small dipoles at the collider energies. We find that already the first heavy ion run at the LHC will allow to study this reaction with sufficient statistics via ultraperipheral collisions hence probing the interaction of q\bar q dipoles of sizes ~ 0.2 fm with nuclear media down to x ~ 10^{-5}.