Exclusive photoproduction of charmonia in $\gamma p \to V p$ and $p p \to p V p$ reactions within $k_t$-factorization approach

TL;DR

This paper calculates the cross sections for exclusive charmonia photoproduction in gamma-proton and proton-proton collisions using a $k_t$-factorization approach, comparing results with HERA, LHCb, and Tevatron data.

Contribution

It introduces a comprehensive $k_t$-factorization calculation including Dirac and Pauli form factors, and assesses the impact of nonlinear gluon effects on experimental data description.

Findings

UGDF with nonlinear effects better fits LHCb data

Good agreement with Tevatron CDF data at midrapidity

Inclusion of Pauli form factor quantifies electromagnetic effects

Abstract

The amplitude for $\gamma p \to J/\psi p$ ($\gamma p \to \psi' p$) is calculated in a pQCD $k_{T}$-factorization approach. The total cross section for this process is calculated for different unintegrated gluon distributions and compared with the HERA data and the data extracted recently by the LHCb collaboration. The amplitude for $\gamma p \to J/\psi p$ ($\gamma p \to \psi' p$) is used to predict the cross section for exclusive photoproduction of $J/\psi$ ($\psi'$) meson in proton-proton collisions. Compared to earlier calculations we include both Dirac and Pauli electromagnetic form factors. The effect of Pauli form factor is quantified. Absorption effects are taken into account and their role is discussed in detail. Different differential distributions e.g. in $J/\psi$ ($\psi'$) rapidity and transverse momentum are presented and compared with existing experimental data. The UGDF with nonlinear effects built in better describe recent experimental data of the LHCb collaboration but no definite conclusion on onset of saturation can be drawn. We present our results also for the Tevatron. A good agreement with the CDF experimental data points at the midrapidity for both $J/\psi$ and $\psi'$ is achieved.