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Two-gluon form factor of the nucleon and $J/ψ$ photoproduction

Leonid Frankfurt, Mark Strikman

TL;DR

The paper proposes a dipole parameterization for the nucleon's two-gluon form factor $Γ(t) = (1 - t/m_{2g}^2)^{-2}$ with $m_{2g}^2 \approx 1 GeV^2$, derived from GPD-based factorization and the transverse squeezing of the vector-meson wave function. It tests this form against a broad set of vector-meson production data, showing that it describes the t-dependence of J/ψ photoproduction from threshold to high energies and is compatible with φ production near threshold. The findings suggest a more compact gluon spatial distribution than the electromagnetic charge distribution and reveal how the t-slope evolves with energy due to Gribov diffusion suppression in hard processes. The work has implications for diffractive dynamics, nucleon structure, and Monte Carlo modeling of high-energy hadronic collisions, and it outlines future measurements (Υ production, JLab 12 GeV) to further validate the approach.

Abstract

We argue that the t-dependence of the two-gluon form factor of the nucleon should be given by $Γ(t)=(1-t/m_{2g}^2)^{-2}$ with $m_{2g}^2\approx 1 GeV^2$. We demonstrate that this form provides a good description of the t-dependence of the cross section of the elastic photoproduction of $J/ψ$-mesons between the threshold region of $E_γ=11 GeV$ (Cornell), $E_γ=19 GeV$ (SLAC) and $E_γ=100 GeV$ (FNAL) including the strong energy dependence of the t-slope. It is also well matched with the recent HERA data. The same assumption explains also the t-dependence of $φ$-meson electroproduction near threshold at $W=2.3 GeV, Q^2=1.0 GeV^2$.

Two-gluon form factor of the nucleon and $J/ψ$ photoproduction

TL;DR

The paper proposes a dipole parameterization for the nucleon's two-gluon form factor with , derived from GPD-based factorization and the transverse squeezing of the vector-meson wave function. It tests this form against a broad set of vector-meson production data, showing that it describes the t-dependence of J/ψ photoproduction from threshold to high energies and is compatible with φ production near threshold. The findings suggest a more compact gluon spatial distribution than the electromagnetic charge distribution and reveal how the t-slope evolves with energy due to Gribov diffusion suppression in hard processes. The work has implications for diffractive dynamics, nucleon structure, and Monte Carlo modeling of high-energy hadronic collisions, and it outlines future measurements (Υ production, JLab 12 GeV) to further validate the approach.

Abstract

We argue that the t-dependence of the two-gluon form factor of the nucleon should be given by with . We demonstrate that this form provides a good description of the t-dependence of the cross section of the elastic photoproduction of -mesons between the threshold region of (Cornell), (SLAC) and (FNAL) including the strong energy dependence of the t-slope. It is also well matched with the recent HERA data. The same assumption explains also the t-dependence of -meson electroproduction near threshold at .

Paper Structure

This paper contains 2 sections, 8 equations, 4 figures.

Table of Contents

  1. Theoretical expectations
  2. Comparison with the data

Figures (4)

  • Figure 1: Comparison of the dipole parameterization of the $d\sigma^{\gamma +p \to J/ \psi +p}/dt$ with the data of Binkley at $\left<E_{\gamma}\right>=100~ GeV$.
  • Figure 2: Comparison of the dipole parameterization of the $d\sigma^{\gamma +p \to J/ \psi +p}/dt$ with the data of Camerini at $E_{\gamma}=19~ GeV$
  • Figure 3: Comparison of the dipole parameterization of the $d\sigma^{\gamma +p \to J/ \psi +p}/dt$ with the data of Gittelman at $\left<E_{\gamma}\right>=11 ~GeV$.
  • Figure 4: Comparison of the dipole parameterization of the $d\sigma^{\gamma^* +p \to \phi +p}/dt$ with the data of Jlab at $\left<W\right>=2.3 ~GeV, \left<Q^2\right>=1 ~GeV^2$.