First Observation of the Directed Flow of $D^{0}$ and $\overline{D^0}$ in Au+Au Collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV

Abstract

We report the first measurement of rapidity-odd directed flow (v1) for D0 and D0― mesons at mid-rapidity (|y|<0.8) in Au+Au collisions at sNN = 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. In 10-80% Au+Au collisions, the slope of the v1 rapidity dependence (dv1/dy), averaged over D0 and D0― mesons, is -0.080 ± 0.017 (stat.) ± 0.016 (syst.) for transverse momentum pT above 1.5 GeV/c. The absolute value of D0-meson dv1/dy is about 25 times larger than that for charged kaons, with 3.4σ significance. These data give a unique insight into the initial tilt of the produced matter, and offer constraints on the geometric and transport parameters of the hot QCD medium created in relativistic heavy-ion collisions.