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Introductory lectures on jet quenching in heavy ion collisions

Jorge Casalderrey-Solana, Carlos A. Salgado

TL;DR

The work derives the medium-induced gluon radiation spectrum from Wilson-line formalism and develops a comprehensive jet-quenching framework linking microscopic parton energy loss to a macroscopic transport coefficient $\hat q$. It then demonstrates phenomenological implementations, including medium-modified fragmentation functions, high-$p_T$ yield suppression, and jet observables, while also exploring medium expansion and heavy-quark mass effects. Beyond perturbation theory, the text surveys AdS/CFT approaches to jet quenching and momentum broadening in $\mathcal{N}=4$ SYM, highlighting strong-coupling insights such as $\hat q$-scaling with $T$ and velocity-dependent broadening, and the drag force on moving probes. Together, the material provides a unified perturbative and holographic perspective on the quark-gluon plasma, with direct implications for RHIC and LHC jet phenomenology.

Abstract

Jet quenching has become an essential signal for the characterization of the medium formed in experiments of heavy-ion collisions. After a brief introduction to the field, we present the full derivation of the medium-induced gluon radiation spectrum, starting from the diagrammatical origin of the Wilson lines and the medium averages and including all intermediate steps. The application of this spectrum to actual phenomenological calculations is then presented, making comparisons with experimental data and indicating some improvements of the formalism to the future LHC program. The last part of the lectures reviews calculations based on the AdS/CFT correspondence on the medium parameters controlling the jet quenching phenomenon.

Introductory lectures on jet quenching in heavy ion collisions

TL;DR

The work derives the medium-induced gluon radiation spectrum from Wilson-line formalism and develops a comprehensive jet-quenching framework linking microscopic parton energy loss to a macroscopic transport coefficient . It then demonstrates phenomenological implementations, including medium-modified fragmentation functions, high- yield suppression, and jet observables, while also exploring medium expansion and heavy-quark mass effects. Beyond perturbation theory, the text surveys AdS/CFT approaches to jet quenching and momentum broadening in SYM, highlighting strong-coupling insights such as -scaling with and velocity-dependent broadening, and the drag force on moving probes. Together, the material provides a unified perturbative and holographic perspective on the quark-gluon plasma, with direct implications for RHIC and LHC jet phenomenology.

Abstract

Jet quenching has become an essential signal for the characterization of the medium formed in experiments of heavy-ion collisions. After a brief introduction to the field, we present the full derivation of the medium-induced gluon radiation spectrum, starting from the diagrammatical origin of the Wilson lines and the medium averages and including all intermediate steps. The application of this spectrum to actual phenomenological calculations is then presented, making comparisons with experimental data and indicating some improvements of the formalism to the future LHC program. The last part of the lectures reviews calculations based on the AdS/CFT correspondence on the medium parameters controlling the jet quenching phenomenon.

Paper Structure

This paper contains 34 sections, 204 equations, 18 figures.

Table of Contents

  1. Contents of the lectures
  2. Heavy-ion collisions and extreme QCD matter
  3. Heavy-ion collisions to characterize hot QCD states
  4. Hard probes to heavy-ion collisions
  5. Hard processes as probes of the medium
  6. Nuclear parton distribution functions
  7. Particle propagation in matter
  8. Wilson lines, eikonal approximation
  9. Relaxing the eikonal approximation
  10. The medium averages
  11. A simple application: the dipole model
  12. Relation with the momentum broadening
  13. The medium--induced gluon radiation
  14. The gluon emission vertex
  15. The medium-induced gluon radiation
  16. ...and 19 more sections

Figures (18)

  • Figure 1: Left: Entropy, $s\equiv \varepsilon+p$ in units of $T^4$ versus temperature computed in lattice. Right: Trace anomaly in units of $T^4$ as a function of the temperature. Figures from Cheng:2007jq
  • Figure 2: Ratios of nuclear to free proton PDFs for different flavors at the initial scale $Q_0^2$=1.69 GeV$^2$ from Eskola:2007my with error estimates. The green line in the gluon panel is an attempt to check the strongest gluon shadowing supported by present data.
  • Figure 3: A multiple scattering eikonal trajectory
  • Figure 4: Different contributions to the dipole cross section
  • Figure 5: The medium-induced gluon radiation diagram.
  • ...and 13 more figures