pQCD vs. AdS/CFT Tested by Heavy Quark Energy Loss

TL;DR

This paper compares predictions from weakly coupled pQCD and strongly coupled AdS/CFT models for heavy quark energy loss in nuclear collisions, highlighting differences in observable ratios at LHC and RHIC.

Contribution

It introduces a novel observable, the double ratio of charm to bottom nuclear modification factors, to distinguish between the two theoretical approaches.

Findings

At LHC, R^{cb} approaches 1 in pQCD and 0.2 in AdS/CFT.

Differences in R^{cb} are less pronounced at RHIC due to spectral and temperature effects.

The momentum dependence of energy loss differs significantly between the models.

Abstract

We predict the charm and bottom quark nuclear modification factors using weakly coupled pQCD and strongly coupled AdS/CFT drag methods. The log(pT/M_Q)/pT dependence of pQCD loss and the momentum independence of drag loss lead to different momentum dependencies for the R_{AA} predictions. This difference is enhanced by examining a new experimental observable, the double ratio of charm to bottom nuclear modification factors, R^{cb}=R^c_{AA}/R^b_{AA}. At LHC the weakly coupled theory predicts R^{cb} goes to 1; whereas the strongly coupled theory predicts R^{cb} .2 independent of pT. At RHIC the differences are less dramatic, as the production spectra are harder, but the drag formula is applicable to higher momenta, due to the lower temperature.