Nuclear shadowing

TL;DR

The article surveys nuclear shadowing at small x in deep-inelastic scattering, explaining it as a consequence of multiple scattering and reviewing three broad theoretical frameworks: Glauber-like rescatterings, Gribov inelastic shadowing, and high-density QCD. It contrasts these with DGLAP-based evolutions of nuclear parton distributions and analyzes how different models fare against available data on F2 and gluon densities, highlighting sizable uncertainties, especially for gluons at x < 0.02. The work emphasizes the relative strengths and limitations of each approach, showing that experimental constraints at very small x are still insufficient to discriminate models definitively. It also discusses the implications for high-energy nuclear collisions and the need for new data from future facilities, such as an Electron-Ion Collider or UPC measurements, to sharpen predictions and understand shadowing in nuclei.

Abstract

The phenomenon of shadowing of nuclear structure functions at small values of Bjorken-$x$ is analyzed. First, multiple scattering is discussed as the underlying physical mechanism. In this context three different but related approaches are presented: Glauber-like rescatterings, Gribov inelastic shadowing and ideas based on high-density Quantum Chromodynamics. Next, different parametrizations of nuclear partonic distributions based on fit analysis to existing data combined with Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution, are reviewed. Finally, a comparison of the different approaches is shown, and a few phenomenological consequences of nuclear shadowing in high-energy nuclear collisions are presented.

Figures (19)

• Figure 1: Diagram of leptoproduction on a nucleus through virtual photon exchange.
• Figure 2: Schematic behaviour of $R_{F_2}^A(x,Q^2)$ as a function of $x$ for a given fixed $Q^2$.
• Figure 3: Plot on the left: Kinematical range in the $x$-$Q^2$ plane probed in nuclear DIS Amaudruz:1995tqArneodo:1995csArneodo:1996rvArneodo:1996ruAdams:1992nfAdams:1995isArnold:1983mwArneodo:1988aaArneodo:1989sy and Drell-Yan Alde:im processes, and in d-Au at forward rapidities Arsene:2004uxAdler:2004eh at RHIC. [Figure taken from d'Enterria:2004nv.] Plot on the right: The average values of $x$ and $Q^2$ of the DIS data from the New Muon Collaboration Amaudruz:1995tqArneodo:1995csArneodo:1996rvArneodo:1996ru (triangles) and E665 Adams:1992nfAdams:1995is (diamonds) in $l$-$A$, and of $x_2$ and $M^2$ of the Drell-Yan dilepton data Alde:im (squares) in p-$A$. The heavy quark mass scales are shown by the horizontal dashed lines. Those lines labeled saturation indicate the estimated saturation scale in proton and Pb. The different bands and lines show the values of $x$ and $Q^2$ which are or will be probed in Drell-Yan or heavy flavour production at SPS, RHIC and LHC, for rapidities different from central ones when indicated. [Figure taken from Accardi:2003be.] See also the text in Subsection \ref{['hdqcd']} and in Section \ref{['appli']}.
• Figure 4: One- (left) and two- (right) scattering diagrams, with the corresponding Feynman rules written on them.
• Figure 5: Plots on the left: Nuclear size dependence of the $F_2$-ratios in the Glauber model in Armesto:2002ny for two fixed values of $x$, compared with experimental data Arneodo:1996rv (filled points). Plots on the right: $Q^2$-dependence of the nuclear $F_2$-ratios for two fixed values of $x$, compared with experimental data Arneodo:1996ru (filled points). Open triangles and circles in the plots on the left, and solid and dashed lines in the plots on the right, correspond to different models for the dipole-nucleon cross section. In the experimental points, inner error bars correspond to statistical errors, and the outer ones to statistical plus systematic errors added in quadrature. [Figures taken from Armesto:2002ny.]