Abstract
We investigate photo-production of vector mesons J/Psi and Psi(2s), based on both HERA and LHC data, using 2 fits of unintegrated gluon distributions. The latter are subject to non-linear Balitsky-Kovchegov evolution (Kutak-Sapeta gluon; KS) and linear next-to-leading order Balitsky-Kuraev-Fadin-Lipatov evolution (Hentschinski-Sabio Vera-Salas; HSS gluon) respectively. Apart from extending previous studies to the case of radially excited charmonium Psi(2s), we further use an improved set of charmonium wave functions and provide an estimate of the uncertainties associated with the HSS gluon. While we observe that the difference between linear and non-linear evolution somehow diminishes and a clear distinction between both HSS and KS gluon is no longer possible using the currently available data-set, we find that the differences between both gluon distributions are enhanced for the ratio of the photo-production cross-sections of Psi(2s) and J/Psi vector mesons.
Highlights
Due to its large center of mass energy, the Large Hadron Collider (LHC) provides a unique opportunity to explore the dynamics of strong interactions in the high energy or Regge limit
The skewness correction of [44,45] would yield in our case with the given values for the effective intercept λ, see Eq (5), a correction in the overall normalization which ranges between a factor 0.872 and 1.53. To separate this normalization uncertainty from the uncertainty associated with the description of the energy dependence, on which we focus in this paper, we fit in the following the overall normalization of our theory prediction to low energy H1 data for J=Ψ photo-production [46] and the ratio of Ψð2sÞ and J=Ψ cross section [47]
In this paper we extended previous studies, dedicated to the study of the energy dependence of the exclusive J=Ψ photo-production cross section to Ψð2sÞ vector mesons
Summary
Due to its large center of mass energy, the Large Hadron Collider (LHC) provides a unique opportunity to explore the dynamics of strong interactions in the high energy or Regge limit. The observable is somewhat complementary to the bulk of studies currently undertaken [13,14,15,16,17,18,19,20,21], which attempt to resolve the hadronic final state in order to explore the low x gluon In contrast to those studies, exclusive photo-production of vector mesons allows for a direct observation of the energy dependence of the photo-production cross section which directly translates into the x-dependence of the underlying gluon distribution. While the instability can be removed through an improved scale setting, the growth of the stabilized gluon distribution with energy is too strong and linear evolution does no longer describe the dataset This observation was interpreted as a first indication for the transition toward saturated gluon densities.
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