Abstract

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 vertical bar Y-ee vertical bar 1 in minimum-bias Au + Au collisions at root(NN)-N-S and 200 GeV. The excess mass spectra are consistently described by a model calculation with a broadened p spectral function for Mee 1.1 GeV/c2. The integrated dielectron excess yield at root(NN)-N-S= 19.6 GeV for 0.4 M-ee 0.75 GeV/c(2), normalized to the charged particle multiplicity at mid-rapidity, has a value similar to that in In + In collisions at root(NN)-N-S = 17.3 GeV. For root(NN)-N-S = 200 GeV, the normalized excess yield in central collisions is higher than that at root(NN)-N-S = 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 root(NN)-N-S = 200 GeV is longer than those in peripheral collisions and at lower energies. (C) 2015 The Authors. Published by Elsevier B.V.