Toward an understanding of the $R_{AA}$ and $v_2$ puzzle for heavy quarks

TL;DR

This paper investigates the heavy quark behavior in quark-gluon plasma, showing that temperature-dependent drag coefficients can explain the observed discrepancy between nuclear modification factor and elliptic flow.

Contribution

It introduces four models of temperature-dependent heavy quark drag and diffusion coefficients, demonstrating their impact on $v_2$ while reproducing $R_{AA}$ data.

Findings

Temperature dependence of drag coefficient significantly affects $v_2$.

Different models can produce 2-3 times variation in $v_2$ for the same $R_{AA}$.

All models successfully reproduce experimental $R_{AA}$ at RHIC.

Abstract

One of the primary aims of the ongoing nuclear collisions at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies is to create a Quark Gluon Plasma (QGP). The heavy quarks constitutes a unique probe of the QGP properties. Both at RHIC and LHC energies a puzzling relation between the nuclear modification factor $R_{AA}(p_T)$ and the elliptic flow $v_2(p_T)$ related to heavy quark has been observed which challenged all the existing models.\\ We discuss how the temperature dependence of the heavy quark drag coefficient can address for a large part of such a puzzle. 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 $R_{AA}(p_T)$ experimentally observed at RHIC energy. We have found 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.