The acceptance-corrected dielectron excess mass spectra, where the known hadronic sources have been subtracted from the inclusive dielectron mass spectra, are reported for the first time at mid-rapidity ∣yee∣+ Au collisions at √sNN = 19.6 and 200 GeV. The excess mass spectra are consistently described by a model calculation with a broadened ρ spectral function for Mee < 1.1 GeV/c2. The integrated dielectron excess yield at √sNN = 19.6 GeV for 0.4 < Mee < 0.75 GeV/c2, normalized to the charged particle multiplicity at mid-rapidity, has a value similar to that in ln+ln collisions at √sNN = 17.3 GeV. For √sNN = 200 GeV, the normalized excess yield in central collisions is higher than that at √sNN = 17.3 GeV and increases from peripheral to central collisions. These measurements indicate that the lifetime of the hot, dense medium created in central Au + Au collisions at √sNN = 200 GeV is longer than those in peripheral collisions and at lower energies.
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This work was supported in part by the Offices of NP and HEP within the U.S. DOEOffice of Science, the U.S. NSF, CNRS/IN2P3, FAPESPCNPq of Brazil, the Ministry of Education and Science of the Russian Federation, NNSFC, CAS, MoST and 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 (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., "Energy Dependence of Acceptance-Corrected Dielectron Excess Mass Spectrum at Mid-Rapidity in Au + Au Collisions at √sNN = 19.6 and 200 GeV" (2015). Physics and Astronomy Faculty Publications. 361.