Systematic Comparison of Jet Energy-Loss Schemes in a realistic hydrodynamic medium

TL;DR

This work performs a controlled, cross-method comparison of three jet energy-loss formalisms (BDMPS/ASW, Higher Twist, and AMY) within a single, realistic 3D hydrodynamic medium. By keeping the medium evolution, initial distributions, and vacuum fragmentation fixed, it isolates intrinsic differences among the schemes and tunes each to a single data point via the transport parameter $\hat{q}$. The study finds that all three approaches can describe inclusive $R_{AA}$ reasonably well, but predict notable differences in centrality- and azimuthal-angle–dependent behavior, with significantly different extracted $\hat{q}_0$ values. The results emphasize that discrepancies arise from the internal scales and approximations of each scheme rather than from the medium evolution, and they point to future work incorporating elastic energy loss and multi-particle observables to more stringently distinguish between formalisms.

Abstract

We perform a systematic comparison of three different jet energy-loss approaches. These include the Armesto-Salgado-Wiedemann scheme based on the approach of Baier-Dokshitzer-Mueller-Peigne-Schiff and Zakharov (BDMPS-Z/ASW), the Higher Twist approach (HT) and a scheme based on the approach of Arnold-Moore-Yaffe (AMY). In this comparison, an identical medium evolution will be utilized for all three approaches: not only does this entail the use of the same realistic three-dimensional relativistic fluid dynamics (RFD) simulation, but also includes the use of identical initial parton-distribution functions and final fragmentation functions. We are, thus, in a unique position, not only to isolate fundamental differences between the various approaches, but also to make rigorous calculations for different experimental measurements using "state of the art" components. All three approaches are reduced to a version which contains only one free tunable parameter, this is then related to the well known transport parameter $\hat{q}$. We find that the parameters of all three calculations can be adjusted to provide a good description of inclusive data on $R_{AA}$ versus transverse momentum. However, we do observe slight differences in their predictions for the centrality and azimuthal angular dependence of $R_{AA}$ vs. $p_T$. We also note that the value of the transport coefficient $\hat{q}$ in the three approaches to describe the data differs significantly.

Figures (12)

• Figure 1: A schematic picture of the various scales involved in the modification of jets in dense matter.
• Figure 2: A typical higher twist contribution used to compute the modification of the fragmentation function in medium.
• Figure 3: A ladder diagram evaluated in the AMY formalism
• Figure 4: (Color online) Time evolution of temperature $T^3$, energy-density $\epsilon^{3/4}$  and entropy density $s$ as a function of time $\tau$ in the central cell of the hydrodynamic evolution for Au+Au collisions at RHIC. All curves are normalized to their maximum values at $\tau=0.6$ fm/c.
• Figure 5: (Color online) Nuclear modification factor $R_{AA}$ in $Au$-$Au$ collisions at 0-5% (top) and 20-30% (bottom) centrality calculated in the ASW, HT and AMY approaches compared to data from PHENIX Shimomura:2005en.