Further success of the colour dipole model

TL;DR

The paper tests whether a universal colour dipole cross-section $σ(s^*, r)$, constrained by $F_2$ data, can describe DVCS, $F_2^c$, exclusive $J/ψ$ production, and diffractive structure functions at HERA. It compares three parameterisations (FS04 Regge, FS04 Saturation, CGC Saturation) and finds broad agreement across observables, supporting universality but not decisively distinguishing saturation dynamics with current precision. Saturation effects appear primarily when including low-$Q^2$ data, though differences among models in exclusive channels are typically small within uncertainties. The study highlights the need for improved forward-slope measurements and higher-energy data to robustly test saturation and the limits of the dipole approach.

Abstract

We confront a very wide body of HERA diffractive electroproduction data with the predictions of the colour dipole model. We focus upon three different parameterisations of the dipole scattering cross-section and find good agreement for all observables. There can be no doubting the success of the dipole scattering approach and more precise observations are needed in order to expose its limitations.

Figures (25)

• Figure 1: The colour dipole model for elastic Compton scattering $\gamma^{\ast }p\rightarrow\gamma^{\ast}p$.
• Figure 2: The colour dipole model for the exclusive reactions $\gamma^{\ast }p\rightarrow Ap$.
• Figure 3: Comparison of the H1 DVCS data H105 with the predictions of the three models discussed in the text: $Q^{2}$ dependence at $W=82$ GeV.
• Figure 4: Comparison of the H1 DVCS data H105 with the predictions of the three models discussed in the text: $W$ dependence at $Q^2 = 8.0$ GeV$^2$.
• Figure 5: Comparison of the ZEUS DVCS data zeusdvcs with the predictions of the three models discussed in the text: $Q^{2}$ dependence at $W=89$ GeV.