Nuclear enhancement and suppression of diffractive structure functions at high energies

TL;DR

The paper investigates how nuclear enhancement and suppression of diffractive structure functions emerge at high energies within CGC-based dipole models that incorporate explicit impact-parameter dependence. It compares two CGC-inspired implementations, IPsat (DGLAP-improved) and bCGC (BK-inspired), against HERA diffractive data and then extends the framework to nuclei using a Glauber-like averaging over nucleons. It finds that the $q\bar{q}$ component of diffraction is enhanced in nuclei while the $q\bar{q}g$ component is suppressed, leading to near-A scaling for $F_{2A}^D$ across many kinematics, with distinct $\beta$ and $x_P$ dependences. The work provides predictions for diffractive observables at a future Electron-Ion Collider and emphasizes the crucial role of accurate $b_T$-dependence in nuclear diffraction phenomenology.

Abstract

We compute diffractive structure functions for both protons and nuclei in the framework of Color Glass Condensate models with impact parameter dependence. These models have previously been shown to provide good agreement with inclusive F_2 measurements and exclusive vector meson measurements at HERA. For nuclei, they provide good (parameter free) agreement with the inclusive F_2 data. We demonstrate good agreement of our computations with HERA measurements on inclusive diffraction. We extend our analysis to nuclei and predict the pattern of enhancement and suppression of the diffractive structures functions that can be measured at an Electron Ion Collider. We discuss how the impact parameter dependence crucially affects our analysis, in particular for large invariant masses at fixed Q^2.

Figures (12)

• Figure 1: Kinematics of diffractive DIS.
• Figure 2: $\beta$-dependence of the different contributions to the proton diffractive structure function at $Q^2=5\textrm{ GeV}^2$ and ${x_\mathbb{P}} = 10^{-3}$.
• Figure 3: $b$-dependence of the the inclusive structure function and different contributions to the diffractive structure function at $Q^2 = 1 \textrm{ GeV}^2$ (a) and $Q^2 = 100 \textrm{ GeV}^2$ (b) for $x = 10^{-3}$ (inclusive) and ${x_\mathbb{P}}=10^{-3}$ (diffractive). In plot (b) ($Q^2 = 100 \textrm{ GeV}^2$) the $b$-dependence of the inclusive cross section and $q\bar{q}g$-components are indistinguishable.
• Figure 4: Comparison of the IPsat and bCGC fits to HERA data on diffractive structure functions.
• Figure 5: The ratio ${{F_{2A}^\textrm{D}}}^x/(A {{F_{2p}^\textrm{D}}}^x)$ in the IPsat model for different components of the diffractive structure function ($x=T,L,q\bar{q}g$) as a function of $\beta$ for gold at $Q^2 = 5 \textrm{ GeV}^2$ and ${x_\mathbb{P}} = 10^{-3}$ without nuclear breakup.