Charm quark evolution in the early stages of heavy-ion collisions

TL;DR

The paper investigates whether charm quark pre-equilibrium dynamics imprint on final heavy-flavor observables in heavy-ion collisions. Using a multi-stage framework combining IP-Glasma, MUSIC, UrQMD, PYTHIA charm production, and Langevin transport with lattice-QCD-based diffusion, the study finds substantial early momentum broadening during the Glasma phase, but only modest effects on D-meson $R_{AA}$ and $v_2$, with changes largely within model uncertainties. The results emphasize the importance of event-by-event fluctuations and lattice-QCD uncertainties in shaping predictions, while suggesting that current observables may be insensitive to early-time charm dynamics. The work motivates further refinement of Glasma-quark interactions and exploration of alternative observables to probe the pre-hydrodynamic stage more sensitively.

Abstract

Heavy quarks are predominantly generated at the initial stage of relativistic heavy-ion collisions such that heavy flavor observables have the potential to provide information on the pre-equilibrium medium dynamics. In this study, we investigate the sensitivity of D-meson $R_{AA}$ and $v_2$ to early-time charm quark dynamics in Pb+Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV. We employ the IP-Glasma+MUSIC+UrQMD framework to model the evolution of the bulk medium. Charm quarks are generated using PYTHIA with nuclear parton distribution functions and evolved using Langevin dynamics within MARTINI. We observe that even though there is significant momentum broadening in the earliest stage, D-meson $R_{AA}$ and $v_2$ are only weakly sensitive to pre-equilibrium interactions.

Figures (9)

• Figure 1: Charm quark locations within the surrounding medium at $\tau = 1.5$ fm at mid-rapidity.
• Figure 2: Momentum dependence of drag (left panel) and diffusion (right panel) coefficients
• Figure 3: Probability of a charm quark coalescing into a meson, baryon, or hadron.
• Figure 4: D-meson $R_{AA}$ and $v_2$ with and without charm quark pre-equilibrium evolution at different centralities. Experimental data taken from ALICE:2021rxaALICE:2020iug.
• Figure 5: Impact of event-by-event (ebe) versus averaged hydro background on charm observables. Experimental data taken from ALICE:2021rxaALICE:2020iug.