Signs for the onset of gluon saturation in exclusive photo-production of vector mesons

Abstract

We investigate the energy dependence of the photo-production cross-section of vector mesons J/Ψ and ϒ, measured by both HERA experiments H1 and ZEUS in electron-proton collisions and by LHC experiments ALICE, CMS and LHCb in ultra-peripheral proton-proton and ultraperipheral proton-lead collisions. Our study uses 2 particular fits of inclusive unintegrated gluon distribution, 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 BFKL evolution can only describe production at highest energies, if perturbative corrections are increased to unnaturally large values; rendering this corrections small, the growth with energy is too strong in the LHC region and the description of J/Ψ data fails. For the KS gluon we find that an accurate description of J/Ψ data is possible if non-linear corrections to low x QCD evolution are taken into account; without such correction a description of data fails. We interpret this observation as a clear signal for the presence of high gluon densities in low x the proton, characteristic for the onset of gluon saturation.

Entangelement entropy in high energy collisions of electrons and protons

“…We find this observation very encouraging and believe that it justifies further investigations into this direction. For further discussion of related aspects and a new proposal related to diffractive DIS, we refer the interested reader to the publications [6,7] as well as our recent preprint [8].…”

“…In the following we will present a few details on this model as well its applications to phenomenology. For more details we refer the interested reader to the publications [6,7] as well as our recent preprint [8], which deals with the extension of the formalism to diffractive DIS.…”

Exclusive Photo-production of J/Ψ and Ψ(2s) as a tool to explore the transition to high and saturated gluon densities at the LHC.

“…In this work we do not assume a constant λ, but determine instead the slope λ from the x-dependent imaginary part of the scattering amplitude, see also [4][5][6][7][8][9][10].…”