Impact of high-energy resummation and GPD evolution on exclusive heavy-quarkonium photoproduction at NLO

In these proceedings, we introduce and discuss the infamous scale-stability problem of exclusive heavy-quarkonium photoproduction off protons in Collinear Factorisation (CF) at next-to-leading order (NLO) in the strong coupling 𝛼𝑠 . We confirm this issue and propose a resolution to the problem by resumming leading-logarithmic QCD corrections via High-Energy Factorisation (HEF) in the Doubly-Leading-Logarithmic Approximation (DLA), matched to CF. Our NLO CF ⊕ DLA HEF predictions show good agreement with HERA and LHC data and exhibit significantly reduced scale dependence compared to Born-level results. We assess the relative impact of uncertainties arising from different sources, including PDF choice, intrinsic PDF uncertainties and variations of the factorisation and renormalisation scales, and compare them with the corresponding experimental uncertainties. The results bear implications for the interpretation of experimental measurements at past, current, and future facilities, including HERA, the LHC, and the EIC.