Ultra-peripheral nuclear collisions as a source of heavy quarkonia

Abstract

Heavy quarkonium production in ultraperipheral nuclear collisions is described within the QCD dipole formalism. A realistic quarkonium wave functions in the rest frame are calculated solving the Schrödinger equation with a subsequent Lorentz boost to high energy. We rely on several selected Q Q potentials, which provide the best description of quarkonium spectra and decay widths, as well as data on diffractive electroproduction of quarkonia on protons. Nuclear effects are calculated with the phenomenological dipole cross sections fitted to DIS data. Higher twist effect related to the lowest Q Q Fock component of the photon, as well as the leading twist effects, related to higher components containing gluons, are included. The results for coherent and incoherent photoproduction of charmonia and bottomonia on nuclei are in a good accord with available data from the recent UPC measurements at the LHC. They can also be verified in future experiments at the planned electron-ion colliders.

Coherent photoproduction of heavy quarkonia on nuclei

“…[11]) offer new opportunities for measurements of exclusive photo-production of vector mesons on protons and nuclei. Corresponding calculations, performed within the color-dipole approach [12,13], as well as other theoretical descriptions of coherent production of heavy quarkonia in UPC, require improvements. In the present paper, we aim to minimize theoretical uncertainties of the QCD dipole formalism for coherent production on nuclear targets.…”

Momentum transfer dependence of heavy quarkonium electroproduction

“…Photo-and electroproduction of heavy quarkonia represents a unique tool allowing to study diffraction mechanism, saturation phenomena, gluon distribution functions, etc. However, for a proper analysis of a given effect associated with the corresponding electroproduction process, it is essential to know various theoretical uncertainties, such as the Q − Q interaction potential, which generates quarkonium wave functions [1], the Q Q → V vertex structure in connection with an open question about a contribution of the D-wave component in quarkonium wave functions [2], or the shape of dipole cross section σ Q Q, which represents one of the main ingredients within the color dipole formalism [1,3].…”

Electroproduction of heavy quarkonia: significance of dipole orientation

“…Elastic real and virtual photoproduction of heavy quarkonia on protons is an effective tool for study of the space-time pattern of diffraction mechanism, as well as related aspects of quantum-chromodynamics (QCD). The long-standing history of our investigation of the photo-and electroproduction of vector mesons [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] has provided the foundations for theoretical interpretation and has contributed in an essential way to understanding of this process within the QCD color dipole formalism. Such a formalism has been frequently used recently in the literature with only minor improvements in corresponding model descriptions.…”

“…Section IV contains expressions for calculation of t-dependent differential cross sections as well as forward diffraction slopes within the LF color dipole formalism. In order to exclude a spurious D-wave admixture, here we treat a simple non-photon-like structure of the V → Q Q transition in the Q Q rest frame as in our previous studies [14][15][16][17][18]. This requires to perform, besides the standard Lorentz boost [35] to the LF frame of radial components of quarkonium wave functions, also transformation of the corresponding spin-dependent parts known as the Melosh spin rotation [36].…”