# Measurement of $D^0$ azimuthal anisotropy at mid-rapidity in Au+Au collisions at \sNN = 200\,GeV

## TL;DR

This paper reports the first measurement of the elliptic flow ($v_2$) of $D^0$ charm mesons in Au+Au collisions at 200 GeV, showing charm quarks reach thermal equilibrium with the medium, consistent with hydrodynamic models.

## Contribution

It provides the first $v_2$ measurement of $D^0$ mesons at RHIC and demonstrates charm quarks' thermalization in the quark-gluon plasma.

## Key findings

- $D^0$ $v_2$ matches hydrodynamic predictions for $p_T<4$ GeV/c.
- Charm $v_2$ is similar to light mesons in 10-40 ext{ }centrality.
- Models with specific charm diffusion coefficients reproduce the results.

## Abstract

We report the first measurement of the elliptic anisotropy ($v_2$) of the charm meson $D^0$ at mid-rapidity ($|y|$\,$<$\,1) in Au+Au collisions at \sNN = 200\,GeV. The measurement was conducted by the STAR experiment at RHIC utilizing a new high-resolution silicon tracker. The measured $D^0$ $v_2$ in 0--80\% centrality Au+Au collisions can be described by a viscous hydrodynamic calculation for transverse momentum ($p_{\rm T}$) less than 4\,GeV/$c$. The $D^0$ $v_2$ as a function of transverse kinetic energy ($m_{\rm T} - m_0$, where $m_{\rm T} = \sqrt{p_{\rm T}^2 + m_0^2}$) is consistent with that of light mesons in 10--40\% centrality Au+Au collisions. These results suggest that charm quarks have achieved local thermal equilibrium with the medium created in such collisions. Several theoretical models, with the temperature--dependent, dimensionless charm spatial diffusion coefficient ($2{\pi}TD_s$) in the range of $\sim$2--12, are able to simultaneously reproduce our $D^0$ $v_2$ result and our previously published results for the $D^0$ nuclear modification factor.