Comparison of Jet Quenching Formalisms for a Quark-Gluon Plasma "Brick"

TL;DR

This paper surveys perturbative QCD–based jet quenching formalisms for radiative energy loss of a fast parton in a dense medium and compares them in a simplified QGP brick setting with fixed lengths. It contrasts ASW, opacity expansion (DGLV/ASW SH), AMY, BDMPS Z, and Higher Twist approaches, highlighting how medium modeling, kinematic limits, and multi-gluon emission schemes shape gluon spectra and energy loss. The brick comparisons reveal sizable quantitative differences even when tuned to the same suppression level, largely due to large angle radiation and how energy-momentum constraints are implemented. The study calls for improved control of large-angle/large-energy radiation, consistent treatment of multiple emissions, and standardized medium descriptions to enable robust extraction of medium properties from data.

Abstract

We review the currently available formalisms for radiative energy loss of a high-momentum parton in a dense strongly interacting medium. The underlying theoretical framework of the four commonly used formalisms is discussed and the differences and commonalities between the formalisms are highlighted. A quantitative comparison of the single gluon emission spectra as well as the energy loss distributions is given for a model system consisting of a uniform medium with a fixed length of L=2 fm and L=5 fm (the `Brick'). Sizable quantitative differences are found. The largest differences can be attributed to specific approximations that are made in the calculation of the radiation spectrum.

Figures (25)

• Figure 1: Schematic view of a hard parton-parton interactions (grey blob) producing a highly energetic parton, which subsequently undergoes parton branching processes. In a heavy ion collision, this parton evolution occurs within a dense medium (blue area) that interferes with the vacuum evolution via a priori unknown elastic and inelastic interactions.
• Figure 2: The landscape of pQCD based jet quenching formalisms. Arrows indicate common concepts or assumptions between adjacent formalisms.
• Figure 3: Energy spectrum of radiated gluons, for a light quark with energy $E=100$ GeV and path length $L=5$ fm (top panel) and for a light quark with $E=10$ GeV and $L=2$ fm (lower panel). The legends on the plots indicate the average energy loss and the corresponding value of the transport coefficient $\hat{q}$.
• Figure 4: Energy loss probability density $P(\Delta E)$ for a light quark of energy $E=100$ GeV and path length $L=5$ fm (top panel) and $E=10$ GeV and $L=2$ fm. The different lines are for different average energy loss, as indicated in the legend, together with the corresponding values of the transport coefficient $\hat{q}$.
• Figure 5: Single inclusive gluon radiation distribution, $dN_g/dx$, from the WHDG implementation of the first order in opacity DGLV formula, Eq. (\ref{['WHDG:DGLV']}), in red, and the ASW--SH implementation of Eq. (\ref{['WHDG:ASW']}), in black, for a 10 GeV up quark traversing a nominal, 2 fm long static brick of QGP held at a constant $T=485$ MeV. The point at $x=1$ indicates the integrated weight of $dN_g/dx$ in the ASW--SH implementation for $x>1$.