Color dipole phenomenology of diffractive electroproduction of light vector mesons at HERA

TL;DR

The paper develops a color dipole description of diffractive electroproduction of light vector mesons, linking the scattering amplitude to a universal dipole cross section σ(x_eff,r) that evolves with energy. It highlights the scanning phenomenon, where the dominant dipole size is set by Q^2+m_V^2, and predicts a pronounced node-driven anomaly for 2S states due to the radial wave-function node. The authors test the framework against extensive data for ρ^0 and φ^0, extract σ(x_eff,r) from vector-meson production, and show consistency with the gBFKL picture and flavor universality. They also forecast rich Q^2 and energy dependencies for radially excited 2S mesons and propose experimental avenues (e.g., Söding-Pumplin interference) to distinguish 2S from D-wave states, thereby illuminating the soft-hard transition in QCD diffractive dynamics.

Abstract

We develop the color dipole phenomenology of diffractive photo- and electroproduction $γ^{*}\,N\rightarrow V(V')\,N$ of light vector mesons ($V(1S) = φ^0, ω^0, ρ^0$) and their radial excitations ($V'(2S) = φ', ω', ρ'$). The node of the radial wave function of the $2S$ states in conjunction with the energy dependence of the color dipole cross section is shown to lead to a strikingly different $Q^2$ and $ν$ dependence of diffractive production of the $V(1S)$ and $V'(2S)$ vector mesons. We discuss the restoration of flavor symmetry and universality properties of production of different vector mesons as a function of $Q^{2}+m_{V}^{2}$. The color dipole model predictions for the $ρ^{0}$ and $φ^{0}$ production are in good agreement with the experimental data from the EMC, NMC, ZEUS and H1 collaborations. We present the first direct evaluation of the dipole cross section from these data.