We report the STAR measurements of dielectron (e+e) production at midrapidity (|yee|SNN=200  GeV. The measurements are evaluated in different invariant mass regions with a focus on 0.30–0.76 (ρ-like), 0.76–0.80 (ω-like), and 0.98–1.05 (ϕ-like)   GeV/c2. The spectrum in the ω-like and ϕ-like regions can be well described by the hadronic cocktail simulation. In the ρ-like region, however, the vacuum ρ spectral function cannot describe the shape of the dielectron excess. In this range, an enhancement of 1.77±0.11(stat)±0.24(syst)±0.33(cocktail) is determined with respect to the hadronic cocktail simulation that excludes the ρ meson. The excess yield in the ρ-like region increases with the number of collision participants faster than the ω and ϕ yields. Theoretical models with broadened ρ contributions through interactions with constituents in the hot QCD medium provide a consistent description of the dilepton mass spectra for the measurement presented here and the earlier data at the Super Proton Synchrotron energies.

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Published in Physical Review Letters, v. 113, no. 2, article 022301, p. 1-7.

©2014 American Physical Society

The copyright holder has granted permission for posting the article here.

This work is a creation of the STAR Collaboration. 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. For the complete list of authors, please download this article or visit the following link: http://dx.doi.org/10.1103/PhysRevLett.113.022301

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We thank the RHIC Operations Group and RCF at BNL, the NERSC Center at LBNL, the KISTI Center in Korea, and the Open Science Grid consortium for providing resources and support. This work was supported in part by the Offices of NP and HEP 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), 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.

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