Extracting jet quenching parameters from large pT hadron suppression at RHIC/LHC

Abstract

The large pT hadron suppression in high-energy heavy-ion collisions at RHIC/LHC is studied in a NLO pQCD parton model in which the fragmentation function is modified due to jet quenching. The energy loss of the energetic parton jets is incorporated in the modified fragmentation functions which utilize two important parameters to characterize the jet transport properties, the jet transport parameter qˆ0 and the mean free path λ0, both at the initial time τ0 in the center of the fireball created in central AA collisions. We performed a phenomenological study of simultaneous χ2/d.o.f fits to RHIC as well as LHC data to constrain the two parameters for energetic quarks, qˆ0≈1.1±0.2 GeV2/fm and λ0≈0.4±0.03 fm in central Au+ Au collisions at sNN=200 GeV, while qˆ0≈1.7±0.3 GeV2/fm, and λ0≈0.5±0.05 fm in central Pb + Pb collisions at sNN=2.76 TeV. Numerical results for the best fit give a multiple scattering picture for the hard jets with a moderate averaged number of gluon emissions. Based on the best constraints for λ0 and τ0, the estimated value for the mean-squared transverse momentum broadening is moderate which implies that the hard jets go through the medium with small reflection.