Detailed measurement of the e{sup +}e{sup -} pair continuum in p+p and Au+Au collisions at sq root(s{sub NN})=200 GeV and implications for direct photon production

Journal Article · Mon Mar 15 04:00:00 EDT 2010 · Physical Review. C, Nuclear Physics

DOI:https://doi.org/10.1103/PHYSREVC.81.034911· OSTI ID:21386705

Adare, A; Bickley, A A; Ellinghaus, F; Kelly, S; Kinney, E; Nagle, J L; Seele, J; Wysocki, M ^[1]; Afanasiev, S; Isupov, A; Litvinenko, A; Malakhov, A; Peresedov, V; Rukoyatkin, P; Zolin, L ^[2]; Aidala, C; Bjorndal, M T; Chi, C Y; Cole, B A; D'Enterria, D ^[3]

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1. University of Colorado, Boulder, Colorado 80309 (United States)
2. Joint Institute for Nuclear Research, RU-141980 Dubna, Moscow Region (Russian Federation)
3. Columbia University, New York, New York 10027 and Nevis Laboratories, Irvington, New York 10533 (United States)

PHENIX has measured the e{sup +}e{sup -} pair continuum in sq root(s{sub NN})=200 GeV Au+Au and p+p collisions over a wide range of mass and transverse momenta. The e{sup +}e{sup -} 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 cc-bar production, although 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{sup stat}+-1.5{sup syst}+-0.9{sup model}. At low mass (m{sub ee}<0.3 GeV/c{sup 2}) and high p{sub T} (1<p{sub T}<5 GeV/c) an enhanced e{sup +}e{sup -} 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{sub T}, with inverse slope T=221+-19{sup stat}+-19{sup syst} MeV. Hydrodynamical models with initial temperatures ranging from T{sub init}approx =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{sub T}<1 GeV/c the low-mass region shows a further significant enhancement that increases with centrality and has an inverse slope of Tapprox =100 MeV. Theoretical models underpredict the low-mass, low-p{sub T} enhancement.

• OSTI ID: 21386705
• Journal Information: Physical Review. C, Nuclear Physics, Journal Name: Physical Review. C, Nuclear Physics Journal Issue: 3 Vol. 81; ISSN 0556-2813; ISSN PRVCAN
• Country of Publication: United States
• Language: English

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