Toward a solution to the R-AA and nu(2) puzzle for heavy quarks

The heavy quarks constitute a unique probe of the quark-gluon plasma properties. A puzzling relation between the nuclear modification factor R-AA(p(T)) and the elliptic flow v(2)(p(T)) has been observed both at RHIC and LHC energies. Predicting correctly both observables has been a challenge to all 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 nu(2) depending on the temperature dependence of the heavy quark drag coefficient. A non-decreasing drag coefficient as T -> T-C is a major ingredient for a simultaneous description of km (P-T) and nu(2) (p(T)). (C) 2015 The Authors. Published by Elsevier B.V.