Probing the initial longitudinal density profile and electromagnetic field in ultrarelativistic heavy-ion collisions with heavy quarks

TL;DR

This study uses an advanced Langevin and hydrodynamic model to investigate how heavy quarks reveal the initial density and electromagnetic field in ultrarelativistic heavy-ion collisions, providing insights into QGP properties.

Contribution

It introduces a coupled Langevin-hydrodynamic framework to analyze heavy meson directed flow and electromagnetic effects, highlighting the electromagnetic field's dominance at LHC energies.

Findings

Heavy flavor $v_1$ rapidity dependence driven by energy density at RHIC.

Electromagnetic field dominates $v_1$ at LHC energies.

Predictions for heavy flavor decay muons for future experimental tests.

Abstract

Heavy quarks are valuable probes of the electromagnetic field and the initial condition of the quark-gluon plasma (QGP) matter produced in high-energy nuclear collisions. Within an improved Langevin model that is coupled to a (3+1)-dimensional viscous hydrodynamic model, we explore the origin of the directed flow coefficient ($v_1$) of heavy mesons and their decay leptons, and its splitting ($\Delta v_{1}$) between opposite charges. We find that while the rapidity dependence of the heavy flavor $v_1$ is mainly driven by the titled energy density profile of the QGP with respect to the longitudinal direction at the RHIC energy, it is dominated by the electromagnetic field at the LHC energy. The $\Delta v_{1}$ serves as a novel probe of the spacetime evolution profile of the electromagnetic field. Our results of $D$ mesons and their decay electrons are consistent with the available data at RHIC and LHC, and our predictions on the heavy flavor decay muons can be further tested by future measurements.