The medium temperature dependence of jet transport coefficient in high-energy nucleus-nucleus collisions

The medium-temperature T dependence of the jet transport coefficient qhat was studied using the nuclear modification factor RAA(pT) and elliptical flow parameter v2(pT) for large transverse momentum pT hadrons in high-energy nucleus-nucleus collisions. Within a next-to-leading order perturbative QCD parton model for hard scatterings with modified fragmentation functions due to jet quenching controlled by qhat, we check the suppression as well as the azimuthal anisotropy for large pT hadrons, and extract qhat by global fits to RAA(pT) and v2(pT) data in A + A collisions at RHIC and the LHC, respectively. Numerical results from the best fits show that qˆ/T 3 goes down with the local medium temperature T in the parton jet trajectory. Compared with the case of a constant qˆ/T 3 , the going-down T dependence of qˆ/T 3 makes a hard parton jet to lose more energy near Tc and therefore strengthens the azimuthal anisotropy for large pT hadrons. As a result, v2(pT) for large pT hadrons is enhanced by about 10% to fit data better at RHIC/LHC. Considering the first-order phase transition from QGP to the hadron phase and additional energy loss in the hadron phase, v2(pT) is again enhanced by 5-10% at RHIC/LHC.  There are all the numerical results for the RAA, v2, qhat values, and the analysis.