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

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We report on measurements of dielectron (e + e − ) production in Au+Au collisions at a centerof-mass energy of 200 GeV per nucleon-nucleon pair using the STAR detector at RHIC. Systematic measurements of the dielectron yield as a function of transverse momentum (pT) and collision centrality show an enhancement compared to a cocktail simulation of hadronic sources in the low invariant-mass region (Mee < 1 GeV/c 2 ). This enhancement cannot be reproduced by the ρ-meson vacuum spectral function. In minimum-bias collisions, in the invariant-mass range of 0.30 − 0.76 GeV/c 2 , integrated over the full pT acceptance, the enhancement factor is 1.76 ± 0.06 (stat.) ± 0.26 (sys.) ± 0.29 (cocktail). The enhancement factor exhibits weak centrality and pT dependence in STAR's accessible kinematic regions, while the excess yield in this invariantmass region as a function of the number of participating nucleons follows a power-law shape with a power of 1.44 ± 0.10. Models that assume an in-medium broadening of the ρ meson spectral function consistently describe the observed excess in these measurements. Additionally, we report on measurements of ω and φ-meson production through their e + e − decay channel. These measurements show good agreement with Tsallis Blast-Wave model predictions as well as, in the case of the φ-meson, results through its K + K − decay channel. In the intermediate invariant-mass region (1.1< Mee < 3 GeV/c 2 ), we investigate the spectral shapes from different collision centralities. 3Physics implications for possible in-medium modification of charmed hadron production and other physics sources are discussed.

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