2009/12/01 by PHENIX Collaboration, A. Adare
Physics and Astronomy · #nucl-ex
paper · pdf · doi:10.1103/physrevc.81.034911
published as Phys.Rev.C81:034911,2010 · 422 authors from 59 institutions, 56 pages, 50 figures, and 13 tables. Submitted to Physical Review C. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html
arxiv created 2009/12/01 · arxiv updated 2010/04/14
PHENIX has measured the e+e- pair continuum in sqrt(sNN)=200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e+e- yield is compared to the expectations from hadronic sources, based on PHENIX measurements. In the intermediate mass region, between the masses of the phi and the J/psi meson, the yield is consistent with expectations from correlated cbar-c production, though other mechanisms are not ruled out. In the low mass region (below the phi) the p+p inclusive mass spectrum is well described by known contributions from light meson decays. In contrast, the Au+Au minimum bias inclusive mass spectrum in this region shows an enhancement by a factor of 4.7+/-0.4(stat)+/-1.5(syst)+/-0.9(model) At low mass (mee<0.3 GeV/c2) and high pT (1<pT<5 GeV/c) an enhanced e+e- pair yield is observed that is consistent with production of virtual direct photons. This excess is used to infer the yield of real direct photons. In central Au+Au collisions, the excess of the direct photon yield over the p+p is exponential in pT, with inverse slope T=221+/-19(stat)+/-19(syst) MeV. Hydrodynamical models with initial temperatures ranging from Tinit ~=300--600 MeV at times of 0.6--0.15 fm/c after the collision are in qualitative agreement with the direct photon data in Au+Au. For low pT<1 GeV/c the low mass region shows a further significant enhancement that increases with centrality and has an inverse slope of T ~=100 MeV. Theoretical models under predict the low mass, low pT enhancement.