Constraints on the path-length dependence of jet quenching in nuclear collisions at RHIC and LHC

Abstract

Recent data on the high-p T pion nuclear modification factor, R AA (p T ), and its elliptic azimuthal asymmetry, v 2(p T ), from RHIC/BNL and LHC/CERN are analyzed in terms of a wide class of jet-energy loss models coupled to different (2+1)d transverse plus Bjorken expanding hydrodynamic fields. We test the consistency of each model by demanding a simultaneous account of the azimuthal, the transverse momentum, and the centrality dependence of the data at both 0.2 and 2.76 ATeV energies. We find a rather broad class of jet-energy independent energy-loss models dE/dx = κ(T)x z T 2+z ζ q that, when coupled to bulk constrained temperature fields T(x, t), can account for the current data at the χ 2 /d.o.f. < 2 level with different temperature-dependent jet-medium couplings, κ(T), and path-length dependence exponents 0 2. We extend previous studies by including a generic term, 0 < ζ q < 2 + q, to test different scenarios of energy-loss fluctuations. While a previously proposed AdS/CFT jet-energy loss model with a temperature-independent jet-medium coupling as well as a near-T c dominated, pQCD-inspired energy-loss scenario are shown to be inconsistent with the LHC data, once the parameters are constrained by fitting to RHIC results, we find several new solutions with a temperature-dependent κ(T). We conclude that the current level of statistical and systematic uncertainties of the measured data does not allow a constraint on the path-length exponent z to a range narrower than [0 - 2]. © 2014 The Author(s).