Strong directed flow of heavy flavor as a probe of matter distribution in heavy-ion collisions

Abstract

The breaking of longitudinal boost invariance in non-central relativistic heavy ion collisions due to asymmetric local participant densities gives rise to a tilt in the reaction plane of the thermalized fireball. A direct consequence of this is the observed rapidity-odd directed flow v1 of charged particles. We study the directed flow of D and D‾ mesons by evolving the charm quark phase space distribution within Langevin dynamics dragged by matter in the tilted bulk, that itself is evolved according to relativistic hydrodynamics. This gives rise to a directed flow of D and D‾ mesons that is of the same sign but several times larger than that of the observed charged particle v1. Hence, rapidity-odd heavy flavor v1 is an ideal candidate to unravel the longitudinal profile of initial entropy deposition. Further, the electromagnetic fields of the initial stage can also give rise to rapidity-odd v1, however unlike the tilt mechanism the electromagnetic field driven v1 is of opposite signs for D and D‾. We study the interplay of the tilt and the electromagnetic fields on heavy flavor directed flow and compare our model predictions with the preliminary STAR data presented in this conference.