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|<1 in minimum-bias Au+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 In+In 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.
|Number of pages||8|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - Nov 12 2015|
Bibliographical noteFunding Information:
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 , 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.
© 2015 The Authors.
ASJC Scopus subject areas
- Nuclear and High Energy Physics