Diffractive electroproduction of light vector particles: leading Fock-state contribution in the presence of significant higher Fock-state effects

TL;DR

This paper investigates diffractive production of light vector mesons and photons using a color dipole model with wave functions from Dyson-Schwinger equations, highlighting the validity of the leading Fock state approximation at high Q^2 and the special role of phi meson in probing gluon saturation.

Contribution

The study introduces a calculation based on Dyson-Schwinger derived wave functions that matches HERA data without fitting and clarifies the Q^2 range where the leading Fock state approximation is valid for different mesons.

Findings

Leading qar{q} approximation valid for Q^2 > 20 GeV^2 for rho mesons.

Leading qar{q} approximation valid for Q^2 > 10 GeV^2 for phi mesons.

Phi electroproduction is ideal for probing gluon saturation effects.

Abstract

We study exclusive diffractive production of vector mesons and photon using the color dipole model with leading Fock state light front wave functions derived from Dyson Schwinger and Bethe Salpeter equations. New results for the $\phi$ meson and real photon are presented. Without data fitting, our calculation well matches HERA data in certain kinematical domains. The key finding of this paper is that in a color dipole model study for $\rho/\gamma$ and $\phi$, where light quarks are involved, the leading $q\bar{q}$ approximation is valid only when $Q^2$ exceeds $20$ and 10 GeV$^2$ respectively, unlike $J/\psi$ which can be well described for $Q^2\approx 0$ GeV$^2$. This underscores the special role of $\phi$ electroproduction in color dipole picture: it strikes a balance between the large dipole size typical of light mesons and the smaller size associated with high $Q^2$ photons, making it potentially well suited for probing gluon saturation effects.