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

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.