Charm quarks are more hydrodynamic than light quarks in final-state elliptic flow

Abstract

We study the charm quark elliptic flow (v2) in heavy ion as well as small system collisions by tracking the evolution history of quarks of different flavors within a multiphase transport model. The charm quark v2 is studied as a function of the number of collisions the charm quark suffers with other quarks and then compared to the v2 of lighter quarks. We find that the common escape mechanism is at work for both the charm and light quark v2. However, contrary to the naive expectation, the hydrodynamics-type flow is found to contribute more to the final state charm v2 than the light quark v2. This could be explained by the smaller average deflection angle the heavier charm quark undergoes in each collision, so that heavy quarks need more scatterings to accumulate a significant v2, while lighter quarks can more easily change directions with scatterings with their v2 coming more from the escape mechanism. Our finding thus suggests that the charm v2 is a better probe for studying the hydrodynamic properties of the quark-gluon plasma.