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Description
Nuclear modification factor $R_{AA}$ for large $p_T$ single hadron is studied
in a next-to-leading order (NLO) perturbative QCD (pQCD) parton model
with medium-modified fragmentation functions (mFFs) due to jet quenching
in high-energy heavy-ion collisions. The energy loss of the hard partons in the QGP is incorporated in the mFFs which utilize two most
important parameters to characterize the transport properties of the hard parton jets: the jet transport parameter $\hat q_{0}$ and the mean
free path $\lambda_{0}$, both at the initial time $\tau_0$.
A phenomenological study of the experimental data for $R_{AA}(p_{T})$ is performed to constrain the two parameters with simultaneous $\chi^2/{\rm d.o.f}$ fits to RHIC as well as LHC data.
We obtain for energetic quarks $\hat q_{0}\approx 1.1 \pm 0.2$ GeV$^2$/fm and $\lambda_{0}\approx 0.4 \pm 0.03$ fm in central $Au+Au$
collisions at $\sqrt{s_{NN}}=200$ GeV, while $\hat q_{0}\approx 1.7 \pm 0.3$ GeV$^2$/fm, and $\lambda_{0}\approx 0.5 \pm 0.05$ fm in central
$Pb+Pb$ collisions at $\sqrt{s_{NN}}=2.76$ TeV.
Numerical analysis shows that the best fit favors a multiple scattering picture for the energetic jets propagating through the bulk medium,
with a moderate averaged number of gluon emissions. Based on the best constraints for $\lambda_{0}$ and $\tau_0$, 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. [Zhi-Quan Liu, Hanzhong Zhang, Ben-Wei Zhang, Enke Wang，Eur. Phys. J. C (2016) 76:20]
