Abstract
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.
Highlights
T single hadron is studied in a next-to-leading order perturbative QCD parton model with medium-modified fragmentation functions due to jet quenching in high-energy heavy-ion collisions
In this paper we will extract the initial jet transport parameter q0 and the initial mean free path λ0 at initial time τ0 on the bulk medium evolution by comparing the experimental data at Relativistic Heavy Ion Collider (RHIC)/Large Hadron Collider (LHC) with numerical simulations of single hadron yields with large pT in a next-to-leading order (NLO) pQCD parton model, where the EPS09 parametrization set of NLO nuclear parton distribution functions has been used to take into account of possible initial-state cold nuclear matter effects, and a phenomenological model
Our numerical results show that, for energetic parton jets scattering inside the bulk medium at the highest temperature, the average transverse momentum broadening squared at LHC is about twice of that at RHIC
Summary
A + A collisions as compared to p + p collisions. These observed jet quenching patterns in heavy-ion collisions at RHIC/LHC can be described well by different theoretical models [14,15,16,17,18,19,20,21,22,23,24,25] that incorporate parton energy loss induced by multiple parton scattering and gluon bremsstrahlung as it propagates through the dense matter. In this paper we will extract the initial jet transport parameter q0 and the initial mean free path λ0 at initial time τ0 on the bulk medium evolution by comparing the experimental data at RHIC/LHC with numerical simulations of single hadron yields with large pT in a next-to-leading order (NLO) pQCD parton model, where the EPS09 parametrization set of NLO nuclear parton distribution functions (nPDFs) has been used to take into account of possible initial-state cold nuclear matter effects, and a phenomenological model [18,20] for medium-modified fragmentation functions calculated in leading order (LO) at twist-4 in the high-twist approach of jet quenching [36,37,38] has been utilized to incorporate parton energy loss.
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