Systematics of the charged-hadron P_T spectrum and the nuclear   suppression factor in heavy-ion collisions from sqrt{s}=200 GeV to sqrt{s}   =2.76 TeV
  In this paper, our goal is to make a simultaneous analysis of the high- and low-P_T parts of the charged-hadron P_T spectrum measured by the ALICE collaboration in central Pb-Pb collisions at sqrt{s}=2.76 TeV at the Large Hadron Collider (LHC), based on models which have been successfully applied and constrained in Au-Au collisions at Relativistic Heavy Ion Collider (RHIC). For the hydrodynamical modeling with which we obtain the low-P_T spectrum, we have computed the initial conditions based on perturbative QCD (pQCD) minijet production and saturation. The sensitivity of the obtained charged-hadron P_T spectrum on the hydrodynamic model parameters is studied. For the high-P_T part, we apply a number of parton-medium interaction models, which are tuned to describe the nuclear suppression factor R_AA measured at the RHIC in central Au-Au collisions at sqrt{s}=200 GeV. We find that the higher kinematic reach of the LHC, manifest in the hardening of the pQCD parton spectral slope, is in principle very efficient in discriminating the various models. However, due to the uncertainties in the p-p baseline, none of the tested models can be firmly ruled out with the present ALICE data. Comparison with the LHC data in this approach also shows that the matching of the hydrodynamic and pQCD+jet quenching components leaves fairly little room for other hadron production mechanisms in the cross-over region P_T=4-5 GeV. 
Thorsten Renk, Hannu Holopainen, Risto Paatelainen and Kari J. Eskola
hep-ph