Low-$x$ parton densities accounting for absorptive effects and exclusive $J/\psi$ and $\Upsilon$ data from the LHC

Abstract

Based on the combined Deep-Inelastic Scattering (DIS) data from HERA and the exclusive $J/\psi$ and $\Upsilon$ cross sections measured at the LHC, we investigate the role of absorptive corrections on the low-$x$ behaviour of parton distribution functions (PDFs) at low and moderate scales. Using $\texttt{xFitter}$, we study the impact of these data and of non-linear evolution on PDFs at next-to-leading order (NLO) and through the NNLO$^*$ method introduced in a previous work. Finally, we determine the effective size of proton hot spots within this framework and discuss the implications of our results for future global PDF determinations.