The growth with energy of exclusive $J/\Psi$ and $\Upsilon$ photo-production cross-sections and BFKL evolution

TL;DR

This paper demonstrates that NLO BFKL evolution accurately describes the energy dependence of exclusive $J/ ext{ and }\Upsilon$ photoproduction cross-sections on protons, aligning well with HERA and LHC data and supporting BFKL evolution at high energies.

Contribution

The study shows that NLO BFKL evolution, combined with impact factor fits from inclusive DIS, can successfully model the energy dependence of vector meson photoproduction cross-sections at LHC energies.

Findings

NLO BFKL describes the energy dependence of $J/\Psi$ and $\Upsilon$ photoproduction cross-sections.

The framework aligns well with HERA and LHC experimental data.

Normalization adjustments are needed for impact factor fits.

Abstract

We investigate whether NLO BFKL evolution is capable to describe the energy dependence of the exclusive photo-production cross-section of vector mesons $J/\Psi$ and $\Upsilon$ on protons. Our description is based on available NLO BFKL fits of the proton impact factor in inclusive DIS, which allow us to construct the necessary scattering amplitude at zero momentum transfer $t=0$. Assuming an exponential drop-off with $t$, this result allows us to calculate the exclusive photoproduction cross-section. Comparing our results with both HERA data (measured by H1 and ZEUS collaborations in $ep$ collision) and LHC data (measured by ALICE, CMS and LHCb collaborations in ultra-peripheral $pp$ and $pPb$ collision) we find that our framework provides a very good description of the energy dependence of the $J/\Psi$ and $\Upsilon$ photoproduction cross-section, providing therefore further evidence for BFKL evolution at the LHC. The available fits of the proton impact factor require on the other hand an adjustment in the overall normalization.