A linearized Boltzmann--Langevin model for heavy quark transport in hot and dense QCD matter

Abstract: In relativistic heavy-ion collisions, the production of heavy quarks at large transverse momenta is strongly suppressed compared to proton-proton collisions. In addition an unexpectedly large azimuthal anisotropy was observed for the emission of charmed hadrons in non-central collisions. Both observations pose challenges to the theoretical understanding of the coupling between heavy quarks and the quark-gluon plasma produced in these collisions. Transport models for the evolution of heavy quarks in a QCD medium offer the opportunity to study these effects - two of the most successful approaches are based on the linearized Boltzmann transport equation and the Langevin equation. In this work, we develop a hybrid transport model that combines the strengths of both of these approaches: heavy quarks scatter with medium partons using matrix-elements calculated in perturbative QCD, while between these discrete hard scatterings they evolve using a Langevin equation with empirical transport coefficients to capture the non-perturbative soft part of the interaction. With the hybrid transport model coupled to a state-of-the-art event-by-event bulk evolution model based on 2+1D relativistic viscous fluid dynamics, we study the azimuthal anisotropy and nuclear modification factor of heavy quarks in Pb+Pb collisions at $\sqrt{s} = 5.02$ TeV. The parameters of our model are calibrated using a Bayesian analysis comparing to available $D$-meson and $B$-meson data at the LHC. Using the calibrated model, we study the implications on heavy-flavor transport properties and predict novel observables.