The energy dependence of exclusive heavy vector meson photoproduction cross-sections and NLO BFKL evolution

TL;DR

This paper investigates the energy dependence of exclusive heavy vector meson photoproduction cross-sections using NLO BFKL evolution, aiming to identify signs of gluon saturation and non-linear QCD effects at high energies.

Contribution

It introduces a novel approach combining NLO BFKL evolution with different initial condition models to analyze vector meson production and gluon saturation effects.

Findings

NLO BFKL evolution accurately describes nuclear modification for J/ψ with BGK initial conditions.

The model's success depends on the initial condition choice, failing with IP-Sat initial conditions.

Provides evidence for gluon saturation effects at high energies.

Abstract

We study the energy dependence of the cross-section for exclusive photoproduction of vector mesons $J/\psi$ and $\Upsilon$, using a solution to the next-to-leading order (NLO) Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation. Our goal is to use BFKL evolution as a benchmark to provide evidence for the presence of non-linear QCD dynamics and signs for the onset of gluon saturation at highest center of mass energies. Our approach determines initial conditions for the proton from the Bartels-Golec Biernat-Kowalski (BGK) dipole model, and evolves the resulting unintegrated gluon distribution using NLO BFKL evolution. For the nucleus, initial conditions are generated through both the impact parameter dependent saturation model (IP-Sat), using a Wood-Saxon distribution and a $A^{1/3}$ scaling of the saturation scale of the original BGK model. We find that NLO BFKL evolution provides a very good description of the nuclear modification factor for $J/\psi$ production, if initial conditions are generated through a $A^{1/3}$ scaled BGK model, while the description fails, if initial conditions are created using the IP-Sat model.