Abstract

We report the first measurement of rapidity-odd directed flow (v(1)) for D-0 and (D-0) over cap mesons at midrapidity (vertical bar y vertical bar 0.8) in Au + Au collisions at. root s(NN) = 200 GeV using the STAR detector at the Relativistic Heavy Ion Collider. In 10-80% Au + Au collisions, the slope of the v(1) rapidity dependence (dv(1)/dy), averaged over D-0 and (D-0)over cap> mesons, is -0.080 +/- 0.017(stat) +/- 0.016(syst) for transverse momentum p(T) above 1.5 GeV/c. The absolute value of D-0 meson dv(1)/dy is about 25 times larger than that for charged kaons, with 3.4 sigma 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.