Diffractive parton distributions from the saturation model

TL;DR

The paper investigates how diffractive deep inelastic scattering (DIS) can be described within the collinear factorization framework and how diffractive parton distributions (DPDs) can be derived from a saturation-model description. Using the GBW saturation dipole cross section, it computes the diffractive final states (qqbar and qqbar g) to obtain initial diffractive quark and gluon distributions that serve as inputs for DGLAP evolution, leading to an x_IP-factorized, Regge-like energy dependence of the leading-twist structure function. A dominant twist-4 longitudinal qqbar contribution emerges at large beta, breaking universality and improving agreement with data in the small-diffractive-mass region. Overall, the approach provides a perturbative QCD-based picture of diffraction in DIS, linking saturation dynamics to observed diffractive phenomena and clarifying the role of higher-twist effects.

Abstract

We review diffractive deep inelastic scattering (DIS) in the light of the collinear factorization theorem. This theorem allows to define diffractive parton distributions in the leading twist approach. Due to its selective final states, diffractive DIS offers interesting insight into the form of the diffractive parton distributions which we explore with the help of the saturation model. We find Regge-like factorization with the correct energy dependence measured at HERA. A remarkable feature of diffractive DIS is the dominance of the twist-4 contribution for small diffractive masses. We quantify this effect and make a comparison with the data.

Figures (6)

• Figure 1: Kinematic invariants in DIS diffraction.
• Figure 2: The diffractive $q\bar{q}$ and $q\bar{q}g$ contributions to $F_2^{D(3)}$.
• Figure 3: Diffractive quark (\ref{['eq:pdq']}) and gluon (\ref{['eq:pdg']}) distributions (multiplied by $x=x_{I\!\!P}\, \beta$) based on the saturation model as a function of $\beta$ for $x_{{I\!\!P}}=0.0042$ at the initial scale $Q_0^2$.
• Figure 4: The comparison with H1 data H197. The dashed lines correspond to the leading twist contribution with the twist-4 component added, eq. (\ref{['eq:newanal']}). The leading twist contribution is shown by the dotted lines.
• Figure 5: The comparison with ZEUS data ZEUS99. The dashed lines correspond to the leading twist contribution with the twist-4 component added, eq. (\ref{['eq:newanal']}). The leading twist contribution is shown by the dotted lines.