Toward a solution to the $R_{AA}$ and $v_2$ puzzle for heavy quarks

TL;DR

This paper investigates the heavy quark interactions in quark-gluon plasma, showing that the temperature dependence of the drag coefficient is key to resolving discrepancies between observed nuclear modification factors and elliptic flow.

Contribution

It demonstrates that different temperature dependencies of the heavy quark drag coefficient can reconcile experimental data on $R_{AA}$ and $v_2$, highlighting the importance of a non-decreasing drag near the critical temperature.

Findings

Models with non-decreasing drag coefficient near T_c reproduce both $R_{AA}$ and $v_2$ data.

Different temperature dependencies can produce 2-3 times more $v_2$ for the same $R_{AA}$.

Temperature dependence of drag coefficient is crucial for understanding heavy quark dynamics in QGP.

Abstract

The heavy quarks constitutes a unique probe of the quark-gluon plasma properties. Both at RHIC and LHC energies a puzzling relation between the nuclear modification factor $R_{AA}(p_T)$ and the elliptic flow $v_2(p_T)$ has been observed which challenged all the existing models, especially for D mesons. We discuss how the temperature dependence of the heavy quark drag coefficient is responsible for a large part of such a puzzle. In particular, we have considered four different models to evaluate the temperature dependence of drag and diffusion coefficients propagating through a quark gluon plasma (QGP). All the four different models are set to reproduce the same $R_{AA}(p_T)$ observed in experiments at RHIC and LHC energy. We point out that for the same $R_{AA}(p_T)$ one can generate 2-3 times more $v_2$ depending on the temperature dependence of the heavy quark drag coefficient. A non-decreasing drag coefficient as $ T \rightarrow\ T_c \,$ is a major ingredient for a simultaneous description of $R_{AA}(p_T)$ and $v_2(p_T)$.