Toward a solution to the RAA and v2 puzzle for heavy quarks

Abstract

The heavy quarks constitute a unique probe of the quark–gluon plasma properties. A puzzling relation between the nuclear modification factor RAA(pT) and the elliptic flow v2(pT) 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 RAA(pT) observed in experiments at RHIC and LHC energy. We point out that for the same RAA(pT) one can generate 2–3 times more v2 depending on the temperature dependence of the heavy quark drag coefficient. A non-decreasing drag coefficient as T→Tc is a major ingredient for a simultaneous description of RAA(pT) and v2(pT).