Global Constraints from RHIC and LHC on Transport Properties of QCD Fluids in CUJET/CIBJET Framework

TL;DR

This study uses a comprehensive global analysis of RHIC and LHC data within the CUJET framework to constrain the transport properties of QCD fluids, integrating viscous hydrodynamics and lattice QCD constraints.

Contribution

It introduces an updated CUJET/CIBJET framework that combines hydrodynamics, jet energy loss, and lattice QCD data to accurately determine QGP transport coefficients.

Findings

Global $ ext{chi}^2$ minimum at $ ext{alpha}_c \\approx 0.9$ and $c_m \\approx 0.25$

Consistent jet transport coefficient with QCD fluid viscosity near $T_c$

Event-by-event fluctuations do not significantly alter results

Abstract

We report results of a comprehensive global $\chi^2$ analysis of nuclear collision data from RHIC (0.2 ATeV), LHC1 (2.76 ATeV), and recent LHC2 (5.02 ATeV) energies using the updated CUJET framework. The framework consistently combines viscous hydrodynamic fields predicted by VISHNU2+1 (validated with soft $p_T<2$~GeV bulk observables) and the DGLV theory of jet elastic and inelastic energy loss generalized to QGP fluids with an sQGMP color structure, including effective semi-QGP color electric quark and gluon as well as emergent color magnetic monopole degrees of freedom constrained by lattice QCD data. We vary the two control parameters of the model (the maximum value of the running QCD coupling, $\alpha_c$, and the ratio $c_m$ of color magnetic to electric screening scales) and calculate the global $\chi^2(\alpha_c,c_m)$ compared with available jet fragment observables ($R_{AA}, v_2$). A global $\chi^2<2$ minimum is found with $\alpha_c \approx 0.9\pm 0.1$ and $c_m\approx 0.25\pm 0.03$. Using CIBJET, the event-by-event (ebe) generalization of the CUJET framework, we show that ebe fluctuations in the initial conditions do not significantly alter our conclusions (except for $v_3$). An important theoretical advantage of the CUJET and CIBJET frameworks is not only its global $\chi^2$ consistency with jet fragment observables at RHIC and LHC and with non-perturbative lattice QCD data, but also its internal consistency of the constrained jet transport coefficient, $\hat{q}(E,T)/T^3$, with the near-perfect fluid viscosity to entropy ratio ($\eta/s \sim T^3/\hat{q}\sim 0.1-0.2$) property of QCD fluids near $T_c$ needed to account for the low $p_T<2$ GeV flow observables. Predictions for future tests at LHC with 5.44 ATeV Xe + Xe and 5.02 ATeV Pb + Pb are also presented.