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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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.
Adkins, James K.; Fatemi, Renee H.; Ramachandran, Suvarna; Adamczyk, L.; Agakishiev, G.; Aggarwal, M. M.; Ahammed, Z.; Alekseev, I.; Alford, J.; Aparin, A.; Arkhipkin, D.; Aschenauer, E. C.; and Averichev, G. S., "Measurements of Dielectron Production in Au + Au Collisions at √sNN = 200 GeV from the STAR Experiment" (2015). Physics and Astronomy Faculty Publications. 387.