Quantifying jet transport properties via large $p_T$ hadron production

TL;DR

This paper uses a next-to-leading order perturbative QCD model with medium-modified fragmentation functions to quantify jet transport properties in heavy-ion collisions by fitting experimental $R_{AA}$ data, revealing key parameters like $\hat q_{0}$ and $\\lambda_{0}$.

Contribution

It introduces a phenomenological method to extract jet transport parameters from $R_{AA}$ data using NLO pQCD with medium modifications, providing new quantitative insights into jet quenching.

Findings

Estimated $\\hat q_{0}$ and $\lambda_{0}$ values for RHIC and LHC collisions.

Supports a multiple scattering picture with moderate gluon emissions.

Indicates small transverse momentum broadening for jets in the medium.

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.