/ Experiment-Nucl arXiv:0912.0244

Detailed measurement of the $e^+ e^-$ pair continuum in $p+p$ and Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV and implications for direct photon production

Adare, A. ; Afanasiev, S. ; Aidala, C. ; Ajitanand, N.N. ; Akiba, Y. ; Al-Bataineh, H. ; Alexander, J. ; Al-Jamel, A. ; Aoki, K. ; Aphecetche, L. ; Armendariz, R. ; Aronson, S.H. ; Asai, J. ; Atomssa, E.T. ; Averbeck, R. ; Awes, T.C. ; Azmoun, B. ; Babintsev, V. ; Baksay, G. ; Baksay, L. ; Baldisseri, A. ; Barish, K.N. ; Barnes, P.D. ; Bassalleck, B. ; Bathe, S.

Published in: Phys.Rev.
Year: 2010
Vol.: C81
Page No: 034911
Pages: 56

Abstract: PHENIX has measured the e^+e^- pair continuum in sqrt(s_NN)=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 c^bar-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 (m_ee<0.3 GeV/c^2) and high p_T (1<p_T<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 p_T, with inverse slope T=221+/-19(stat)+/-19(syst) MeV. Hydrodynamical models with initial temperatures ranging from T_init ~=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 p_T<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 p_T enhancement.

Total numbers of views: 2114
Numbers of unique views: 825
e-proceeding