Global polarization of Λ hyperons has been measured to be of the order of a few tenths of a percent in Au+Au collisions at √ s N N = 200 GeV, with no significant difference between Λ andΛ.These new results reveal the collision energy dependence of the global polarization together with the results previously observed at √ s N N = 7.7 -62.4 GeV and indicate noticeable vorticity of the medium created in non-central heavy-ion collisions at the highest RHIC collision energy. The signal is in rough quantitative agreement with the theoretical predictions from a hydrodynamic model and from the AMPT (A Multi-Phase Transport) model. The polarization is larger in more peripheral collisions, and depends weakly on the hyperon's transverse momentum and pseudorapidity η H within |η H | < 1. An indication of the polarization dependence on the event-by-event charge asymmetry 3 is observed at the 2σ level, suggesting a possible contribution to the polarization from the axial current induced by the initial magnetic field. PACS numbers: 25.75.-q, 25.75.Ld

No abstract

No abstract

No abstract

We report a new measurement of D 0-meson production at mid-rapidity (|y| < 1) in Au+Au collisions at √ sNN = 200 GeV utilizing the Heavy Flavor Tracker, a high resolution silicon detector at the STAR experiment. Invariant yields of D 0-mesons with transverse momentum pT 9 GeV/c are reported in various centrality bins (0-10%, 10-20%, 20-40%, 40-60% and 60-80%). Blast-Wave thermal models are used to fit the D 0-meson pT spectra to study D 0 hadron kinetic freeze-out properties. The average radial flow velocity extracted from the fit is considerably smaller than that of light hadrons (π, K and p), but comparable to that of hadrons containing multiple strange