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.

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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.