Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Parton Saturation-An Overview

A. H. Mueller

TL;DR

This overview develops the conceptual and technical framework for parton saturation in high-density QCD at small x. It connects light-cone perturbation theory, Wilson-line eikonal methods, and classical gluon field pictures to describe dipole–nucleon scattering, saturation scales Q_S, and unitarity-limited evolution. It surveys both phenomenological models (GBW) and nonlinear evolution equations (Kovchegov, JIMWLK), and introduces the McLerran–Venkino model as a lab for gluon saturation in nuclei, with implications for DIS data and heavy-ion physics. Together, these insights provide a coherent approach to understanding how high-density effects regulate parton densities and manifest in observable cross sections and structure functions.

Abstract

The idea of partons and the utility of using light-cone gauge in QCD are introduced. Saturation of quark and gluon distributions are discussed using simple models and in a more general context. The Golec-Biernat W\usthoff model and some simple phenomenology are described. A simple, but realistic, equation for unitary, the Kovchegov equation, is discussed, and an elementary derivation of the JIMWLK equation is given.

Parton Saturation-An Overview

TL;DR

This overview develops the conceptual and technical framework for parton saturation in high-density QCD at small x. It connects light-cone perturbation theory, Wilson-line eikonal methods, and classical gluon field pictures to describe dipole–nucleon scattering, saturation scales Q_S, and unitarity-limited evolution. It surveys both phenomenological models (GBW) and nonlinear evolution equations (Kovchegov, JIMWLK), and introduces the McLerran–Venkino model as a lab for gluon saturation in nuclei, with implications for DIS data and heavy-ion physics. Together, these insights provide a coherent approach to understanding how high-density effects regulate parton densities and manifest in observable cross sections and structure functions.

Abstract

The idea of partons and the utility of using light-cone gauge in QCD are introduced. Saturation of quark and gluon distributions are discussed using simple models and in a more general context. The Golec-Biernat W\usthoff model and some simple phenomenology are described. A simple, but realistic, equation for unitary, the Kovchegov equation, is discussed, and an elementary derivation of the JIMWLK equation is given.

Paper Structure

This paper contains 13 sections, 100 equations, 20 figures.

Table of Contents

  1. Introduction
  2. States in QCD Perturbation Theory
  3. Partons
  4. Classical Fields
  5. Why Light-Cone Gauge is Special
  6. High Momentum Particles and Wilson Lines$^{3-5}$
  7. Dual Descriptions of Deep Inelastic Scattering; Bjorken and Dipole Frames
  8. Quark Distributions in a large Nucleus; Quark Saturation at One-Loop
  9. Gluon Saturation in a Large Nucleus; the McLerran Venugopalan Model$^{12}$
  10. The Golec-Biernat Wüsthoff Model$^{15}$
  11. Measuring Dipole Cross Sections
  12. A Simple Equation for Unitarity; the Kovchegov equation$^{21}$
  13. A Simple Derivation of the JIMWLK equation$^{[14,25-27]}$