Testing pQCD and AdS/CFT Energy Loss at RHIC and LHC

Abstract

We compare calculations of jet quenching observables at sqrt s = 2.76 ATeV to preliminary LHC data from weak-coupling pQCD and strong-coupling AdS/CFT drag energy loss models. Rigorously constrained to sqrt s = 200 AGeV RHIC pi^0 suppression data and introducing no free parameters, the pQCD-based WHDG model simultaneously describes qualitatively the suppression of light hadrons and quantitatively the azimuthal anisotropy (over many centrality classes) of light hadrons and the suppression of D mesons at LHC. The drag predictions shown here--qualitatively constrained to RHIC data--compare poorly to the measured suppression of D mesons, but the current experimental uncertainties are large. The double ratio of D to B meson R_AA(p_T) should provide a robust experimental measurement to distinguish between the very different assumptions of the strength of interactions in the QGP produced in heavy ion collisions; i.e., whether, from a jet quenching standpoint, the medium is either weakly- or strongly-coupled.