Charm $v_2$ are more hydrodynamic than light quark $v_2$

Abstract

Charm quark $v_{2}$ is a useful tool for studying the properties of quark-gluon plasma because charm quarks experience almost the entire evolution history of relativistic heavy ion collisions. Recent studies with transport models suggest that the majority of the overall quark $v_{2}$ at RHIC energies comes from the anisotropic escape of partons, not from the hydrodynamic flow. To address whether this is also true for the charm quark $v_{2}$, we trace the charm quark $v_{2}$ as a function of the number of collisions the charm quark suffers with other quarks in a multi-phase transport model. We find that the common escape mechanism is at work for both the charm and light quark $v_{2}$. However, contrary to the naive expectation, the hydrodynamic collective flow contributes more to the charm $v_{2}$ than the light quark $v_{2}$. Our finding thus highlights the importance of charm $v_{2}$ in the study of hydrodynamic properties of the quark-gluon plasma.