We present measurements of bulk properties of the matter produced in Au+Au collisions at √ sNN = 7.7, 11.5, 19.6, 27, and 39 GeV using identified hadrons (π ± , K ± , p andp) from the STAR experiment in the Beam Energy Scan (BES) Program at the Relativistic Heavy Ion Collider (RHIC). Midrapidity (|y| <0.1) results for multiplicity densities dN/dy, average transverse momenta pT and particle ratios are presented. The chemical and kinetic freeze-out dynamics at these energies are discussed and presented as a function of collision centrality and energy. These results constitute the systematic measurements of bulk properties of matter formed in heavy-ion collisions over a broad range of energy (or baryon chemical potential) at RHIC.

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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