We report on measurements of dielectron (e+e) production in Au + Au collisions at a center-of-mass energy of 200 GeV per nucleon-nucleon pair using the STAR detector at BNL Relativistic Heavy Ion Collider. 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/c2). This enhancement cannot be reproduced by the ρ-meson vacuum spectral function. In minimumbias collisions, in the invariant-mass range of 0.30–0.76 GeV/c2, 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 invariant-mass 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/c2), we investigate the spectral shapes from different collision centralities. Physics implications for possible in-medium modification of charmed hadron production and other physics sources are discussed.

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Published in Physical Review C, v. 92, no. 2, article 024912, p. 1-35.

©2015 American Physical Society

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Due to the large number of authors involved, only the first 10 and the ones affiliated with the University of Kentucky are listed in the author section above. The authors of this article are collectively known as STAR Collaboration. To see a full list of authors, please download this article or visit: https://doi.org/10.1103/PhysRevC.92.024912

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This work was supported, in part, by the Office of Nuclear Physics within the U.S. DOE Office of Science, the U.S. NSF, CNRS/IN2P3; FAPESP CNPq of Brazil; the Ministry of Education and Science of the Russian Federation; the NNSFC, the MoST of China (973 Program No. 2014CB845400, 2015CB856900), CAS, the MoE of China; the Korean Research Foundation; GA and MSMT of the Czech Republic; FIAS of Germany; DAE, DST, and CSIR of India; the National Science Centre of Poland; National Research Foundation (Grant No. NRF-2012004024); the Ministry of Science, Education and Sports of the Republic of Croatia; and RosAtom of Russia.