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 ≤ z ≤ 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].
Highlights
The corrected figures imply that: (a) The nuclear modification factor RAA at LHC energies for pure elastic energy loss [with (a, b, c, q) = (0, 0, 2, −1)] in the new figure 1 is found to be compatible with both RHIC and LHC energies for κRHIC = κLHC
(b) The SLTc scenario assuming a radiative jet-energy loss coupling κ(T ) that is enhanced by a factor of three in the transition range of 113 < T < 173 MeV [23,24,25] does describe the LHC RAA-data but is sensitive to the bulk hydrodynamic background temperature field
0.2 (b2) LHC, SLTc [κ(T) E0τ1 T3 ζ−1]
Summary
Barbara Betza and Miklos Gyulassyb,c,d aInstitute for Theoretical Physics, Johann Wolfgang Goethe-University, 60438 Frankfurt am Main, Germany bDepartment of Physics, Columbia University, New York, 10027, U.S.A. cNuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA, U.S.A. dInstitute for Particle and Nuclear Physics, Wigner RCP, HAS, 1121 Budapest, Hungary See replacement figures 1 and 2 below.
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