The Physics of Jet Quenching in Perturbative QCD

TL;DR

This work presents a comprehensive, first-principles framework for jet quenching in perturbative QCD, connecting hard jet evolution to medium-induced radiation, color coherence, and emergent, turbulence-like cascades in the quark–gluon plasma. It develops a unified treatment of medium-induced radiation (BDMPS–Z) with radiative corrections to the jet-quenching parameter $\hat{q}$, and derives non-linear evolution equations that govern jet energy loss and the distribution of energy flow outside the jet cone. The framework demonstrates how a gluon cascade redistributes energy toward infrared scales, exhibits geometric scaling in transverse momentum broadening, and encodes color decoherence effects that control coherence vs. decoherence of multi-prong jets. By integrating these advances with non-linear DGLAP-like evolution and jet-function formalisms, the approach connects perturbative jet dynamics to realistic heavy-ion observables, paving the way for precision phenomenology and EFT-based factorization in RHIC and LHC jet data.

Abstract

Hard processes in collider experiments typically produce QCD jets, which have long served as precision tests of QCD in the vacuum. More recently, heavy-ion programs at RHIC and the LHC have offered a novel perspective on jets, establishing them as unique probes of strongly interacting matter. Experimental observations, including the suppression of high-$p_T$ hadrons and jets, provide compelling evidence for the formation of a new state of matter and its strong coupling to energetic partons. These advances have motivated new theoretical approaches to jet quenching that go beyond standard perturbative techniques, aiming to elucidate the mechanisms of energy dissipation and thermalization of energetic partons in the quark-gluon plasma. This review highlights recent progress, beginning with a unified description of medium-induced radiation across the Landau-Pomeranchuk-Migdal regime and its role in turbulent gluon cascades. We then examine radiative corrections that renormalize the transport coefficient $\hat q$, the mechanism of color decoherence in multi-parton systems, and nonlinear QCD evolution equations for jet energy loss. Finally, we confront this framework with experimental measurements, underscoring the need for precision phenomenology to fully exploit the rich data sets from RHIC and the LHC.

Figures (26)

• Figure 1: Illustration of a high-energy parton undergoing energy loss through multiple quasi-instantaneous soft gluon emissions, characterized by the Poisson-like distribution described in Eq. \ref{['eq:poisson']}, in a plasma of length $L$.
• Figure 2: Illustration of a eikonal propagation encoded in Wilson lines. The longitudinal momentum $p^+= E$ of the energetic parton is much larger than the momentum transfers to the medium. The background field is depicted vertical gluon lines.
• Figure 3: Illustration of a non-eikonal propagation in the background field of the plasma. Even though the longitudinal momentum $p^+= E$ of the energetic parton is much larger than the momentum transfers to the medium the large extent of the medium results in non-eikonal effects encoded in the free propagation between interactions.
• Figure 4: Momentum broadening probability distribution at first two orders in in Molière's-expansion compared to the exact solution of the Fourier transform Eq. \ref{['GM-P']} with $\lambda\!=\!0.1$ corresponding to ($Q^2_{\text{med}}\!=\!30$ GeV$^2$, $m^2_D\!=\!0.13$ GeV$^2$). In this and following figures $p_\perp\equiv |{\boldsymbol p}|$. ${\cal P}^{(0)}$ stands for the Gaussian form order $\lambda^0$ in Eq. \ref{['eq:golden']}, while the next order ${\cal P}^{(1)}$ contains the Coulomb tail $1/p_\perp^4$.
• Figure 5: Comparison between the energy spectrum computed with GLV (dotted, purple), the Improved Harmonic oscillator (or improved opacity expansion) at LO (dashed, green), LO+NLO (solid, red), and the all-order spectrum (solid, navy) as computed in Andres:2020vxs. The ratio to the full solution is presented in the bottom panels. The uncertainty band arises from variations in the matching scale, and the gray region indicates the soft BH regime where our approach breaks down. The parameters used $\hat{q}_0 = 0.16$ GeV$^3$, $L = 6$ fm and $m_D = 0.355$ GeV, with $\omega_0 \equiv \hat{q}_0 L^2$.