Extracting $\hat{q}$ from single inclusive data at RHIC and at the LHC for different centralities: a new puzzle?

Abstract

We present here an extraction of the jet transport coefficient, $\hat{q}$, using RHIC and LHC single-inclusive high-$p_T$ data for different centralities. We fit a $K$-factor that determines the deviation of this coefficient from an ideal estimate, $K\equiv \hat{q}/(2{ϵ}^{3/4})$, where $ϵ$ is given by hydrodynamic simulations. As obtained already in previous studies, this $K$-factor is found to be larger at RHIC than at the LHC. However it is, unexpectedly, basically no-dependent on the centrality of the collision. Taken at face value this result, the $K$-factor would not depend on local properties of the QGP as temperature, but on global collision variables such as the center of mass energy.

Comments: 4 pages, 4 figures, proceedings for the 8th International Conference on Hard and Electromagnetic Probes of High-energy Nuclear Collisions (Hard Probes 2016)