Vector Meson Production in the Golec-Biernat Wuesthoff Model

TL;DR

This paper tests the Golec-Biernat-Wusthoff saturation-based color-dipole model for exclusive vector meson production in gamma-star p scattering. By employing several J/psi wavefunction Ansatze (delta, Gaussian, double-Gaussian) and a relativistic light-cone approach for light mesons, the authors compute the forward amplitudes and cross sections for gamma*p -> V p across a range of Q2 and W. The results show robust W dependence for J/psi, consistent with pQCD expectations in the saturation regime, while light mesons reproduce qualitative trends but suffer from normalization issues linked to the wavefunctions and t-slope. Overall, the GBW framework captures key features of exclusive VM production and clarifies where improved meson wavefunctions are needed to fully match data.

Abstract

We apply the Golec-Biernat Wuesthoff model in the calculation of vector meson photo- and electroproduction. Starting from very simple non-relativistic wave functions we show that the model provides a good description of $J/Ψ$ cross sections in wide $Q^2$ and $W$ ranges. For the light mesons one obtains the approximately correct $W$ dependence and ratio of longitudinal to transverse cross sections, although in this case the normalization, affected mainly by the wave function employed, is not in good agreement with data.

Figures (8)

• Figure 1: Scheme for vector meson production in the Color Dipole model.
• Figure 2: The W-dependence of elastic $J/\Psi$ production as a function of $Q^2$. Open circles are ZEUS data ZEUSpsi1ZEUSpsi2 and solid circles H1 data H1psi1H1psi2. The dotted lines correspond to calculations using the $\delta$-function wave function, the dashed lines to calculations using a single Gaussian, and the solid lines to the double Gaussian wavefunction as discussed in the text. The $Q^2$ values, in units of GeV$^2$, are indicated in the figure. The data and calculations have been scaled by the values given for clarity of presentation.
• Figure 3: Ratio $R=\sigma_L/\sigma_T$ for elastic $J/\Psi$ electroproduction. The dotted and dashed lines (superimposed) correspond to the $\delta$ and single Gaussian wave functions. The solid lines are calculated with Double Gaussian wave function. The upper plot gives the $Q^2$ dependence at fixed $W=90$ GeV. The lower plot gives results versus $W$ for $Q^2$ = 6.2 GeV$^2$ (upper curves), and $Q^2$ = 0.45 GeV$^2$ (lower curves). The open circles are ZEUS data ZEUSpsi2 and the solid circles are H1 data H1psi2.
• Figure 4: The $W$-dependence of elastic $\rho$ production as a function of $Q^2$ compared with recent ZEUS ZEUSrho1ZEUSpsi2 and H1 H1rho1H1rho2 data. The $Q^2$ values are given in the plot. The solid lines are for the four quark parameters, while the dashed lines are for the three quark parameter sets.
• Figure 5: The $W$-dependence of elastic $\rho$ production as a function of $Q^2$, compared with recent ZEUS ZEUSpsi2 (open circles) and H1 H1rho2 (solid circles) data. The solid line is the result using the four flavor parameter set, and the dashed curve is the result using the three flavor parameter set.