Curing the high-energy perturbative instability of vector-quarkonium-photoproduction cross sections at order ααs3 with high-energy factorisation

• Published in: The European physical journal. C, Particles and fields Particles and fields, 2024-04, Vol.84 (4), p.351
• Main Authors: Lansberg, Jean-Philippe, Nefedov, Maxim, Ozcelik, Melih A.
• Format: Article
• Language: English
• Subjects: Approximation; Astronomy; Astrophysics and Cosmology; Cross-sections; Distribution functions; Elementary Particles; Factorization; Hadrons; Heavy Ions; Logarithms; Matching; Mathematical analysis; Measurement Science and Instrumentation; Nuclear Energy; Nuclear Physics; Partons; Photoproduction; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Regular Article - Theoretical Physics; S waves; String Theory
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-024-12588-x

We cure the perturbative instability of the total-inclusive-photoproduction cross sections of vector S -wave quarkonia observed at high photon-proton-collision energies ( s γ p ) in Next-to-Leading Order (NLO) Collinear-Factorisation (CF) computations. This is achieved using High-Energy Factorisation (HEF) in the Doubly-Logarithmic Approximation (DLA), which is a subset of the Leading-Logarithmic Approximation (LLA) of HEF which resums higher-order QCD corrections proportional to α s n ln n - 1 ( s ^ / M 2 ) in the Regge limit s ^ ≫ M 2 with M 2 being the quarkonium mass and s ^ is the squared partonic-center-of-mass energy. Such a DLA is strictly consistent with the NLO and NNLO DGLAP evolutions of the parton distribution functions. By improving the treatment of the large- s ^ asymptotics of the CF coefficient function, the resummation cures the unphysical results of the NLO CF calculation. The matching is directly performed in s ^ space using the Inverse-Error Weighting matching procedure which avoids any possible double counting. The obtained cross sections are in good agreement with data. In addition, the scale-variation uncertainty of the matched result is significantly reduced compared to the LO results. Our calculations also yield closed-form analytic limits for s ^ ≫ M 2 of the NLO partonic CF and numerical limits for contributions to those at NNLO scaling like α s 2 ln ( s ^ / M 2 ) .