Momentum transfer squared dependence of exclusive quarkonia photoproduction in ultraperipheral collisions

Cheryl Henkels,Emmanuel G De Oliveira,Roman Pasechnik,Haimon Trebien

doi:10.1103/physrevd.104.054008

Cheryl Henkels, Emmanuel G De Oliveira + Show 2 more

Open Access

https://doi.org/10.1103/physrevd.104.054008

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Abstract

In this paper, we study fully differential quarkonia photoproduction observables in ultraperipheral collisions (UPCs) as functions of momentum transfer squared. We employ the dipole picture of the QCD part of the scattering with proton and nucleus targets, with the projectile being a quasi-real photon flux emitted by an incoming hadron. We analyse such observables for ground $J/\psi$, $\Upsilon(1S)$ and excited $\psi'$, $\Upsilon(2S)$ states whose light-front wave functions are obtained in the framework of interquark potential model incorporating the Melosh spin transformation. Two different low-$x$ saturation models, one obtained by solving the Balitsky--Kovchegov equation with the collinearly improved kernel and the other with a Gaussian impact-parameter dependent profile, are used to estimate the underlined theoretical uncertainties of our calculations. The results for the proton target and with charmonium in the final state are in agreement with the available HERA data, while in the case of nucleus target we make predictions for $\gamma A$ and $AA$ differential cross sections at different $W$ and at $\sqrt{s}=5.02$ TeV, respectively.

Highlights

The determination of the structure of protons and nuclei in terms of their fundamental constituents as well as their interactions is one of the biggest goals of particle physics [1]
A bigger difference is found for the ψð2SÞ cross section computed with the harmonic oscillator potential, which is noticeably higher than the results for other potentials
The impact-parameter b-dependent dipole model has been employed for studies of differential observables of elastic quarkonia photoproduction off proton and nuclear targets

Summary

INTRODUCTION

The determination of the structure of protons and nuclei in terms of their fundamental constituents as well as their interactions is one of the biggest goals of particle physics [1]. Besides exclusive electro- and photoproduction of light vector mesons (φ, ρ) and quarkonia (J=ψ) studied by the H1 and ZEUS collaborations, there are more recent data on vector-meson photoproduction in ultraperipheral collisions (UPCs) available from the LHC The latter processes are the main focus of this work. In the limit of small x ≪ 1 and low four-momentum transfer squared jtj 1⁄4 −ðp1 − p01Þ2 ≪ m2Q, such an exchange in momentum space is usually described in terms of the generalized unintegrated gluon density in the target, which, in turn, connects to the dipole scattering matrix as a function of gluon x, dipole separation r⃗ , and the impact parameter of the scattering b⃗. We apply both the bSat model and the BK solution with a collinearly improved kernel in the study of differential quarkonia photoproduction cross sections in UPCs for relevant experimental conditions at HERA and LHC colliders.

ELASTIC PHOTOPRODUCTION OFF A PROTON

PARTIAL DIPOLE AMPLITUDE

RESULTS

COHERENT PHOTOPRODUCTION OFF NUCLEAR TARGETS

CONCLUSIONS