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

We argue that the process γ+A→J/ψ+"gap"+X at large momentum transfer q2 provides a quick and effective way to test the 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 one to study this reaction with sufficient statistics via ultraperipheral collisions, hence probing the interaction of qq̄ dipoles of sizes ∼0.2fm with nuclear media down to x∼10-5.