Advances in the extraction of jet transport coefficients in high-energy heavy-ion collisions

A series of experimental and theoretical studies have detected and confirmed the jet quenching effect as a hard probe signal of the Quark-Gluon Plasma created in high-energy heavy-ion collisions. The jet transport coefficient, denoted as (q) over cap, can be related to the gluon field strength correlation or the local gluon number density of the strong interaction (QCD) medium along the light-like trajectory of the hard parton, and it quantifies the strength of jet quenching. The (q) over cap extraction via suppression of the final state particle is a frontier subject in high-energy heavy-ion collisions. A series of phenomenological studies have made considerable progress in the extraction of (q) over cap through model-to-data comparisons using hadron suppression data. Early phenomenological studies generally assumed that the (q) over cap was proportional to the cubic temperature. Therefore, in this work, with the assumption (q) over cap = (q) over cap 0T(3)/T-0(3), we first extracted the (q) over cap0, which is the jet transport parameter in the hydrodynamics initial time at the medium highest-temperature T-0. The hadron production spectra can be calculated using the next-to-leading order pQCD parton model with higher-twist parton energy loss. With the experimental data of different particle species, colliding energies, and centralities, the numerical results demonstrate that the value of scaled (q) over cap0/T-0(3) decreases as the T-0 increases. To further study the local temperature dependence of (q) over cap /T-3 in this work, a global constraint on (q) over cap was performed by combining all existing experimental data on single hadron, dihadron, and gamma-hadron suppression at both RHIC and LHC energies across a wide range of centralities. In the face of massive model calculations, we develop an information field (IF) approach to model the prior distribution of the unknown function (q) over cap (T), which is free of long-range correlations. Using the IF approach, the data from low-temperature regions cannot constrain the (q) over cap (T) at higher temperatures. The (q) over cap /T-3 can be constrained progressively when experimental data from more central collisions and higher colliding energies are incrementally included. The global Bayesian analysis using the IF prior provides a stringent constraint on (q) over cap (T), and the obtained (q) over cap /T-3 exhibits a strong T-dependence.