QCD evolution based evidence for the onset of gluon saturation in exclusive photo-production of vector mesons

• Published in: Physics letters. B Vol. 795; pp. 569 - 575
• Main Authors: Arroyo Garcia, A., Hentschinski, M., Kutak, K.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 10.08.2019; Elsevier
• ISSN: 0370-2693; 1873-2445
• DOI: 10.1016/j.physletb.2019.06.061

We investigate photo-production of vector mesons J/Ψ and ϒ measured both at HERA and LHC, using 2 particular fits of inclusive unintegrated gluon distributions, based on non-linear Balitsky-Kovchegov evolution (Kutak-Sapeta gluon; KS) and next-to-leading order Balitsky-Fadin-Kuraev-Lipatov evolution (Hentschinski-Sabio Vera-Salas gluon; HSS). We find that linear next-to-leading order evolution can only describe production at highest energies, if perturbative corrections are increased to unnaturally large values; rendering these corrections to a perturbative size, the growth with energy is too strong and the description fails. At the same time, the KS gluon, which we explore both with and without non-linear corrections, requires the latter to achieve an accurate description of the energy dependence of data. We interpret this observation as a clear signal for the presence of high gluon densities in the proton, characteristic for the onset of gluon saturation.