Detailed Measurement of the e+e- Pair Continuum in p+p and Au+Au Collisions at s_NN = 200 GeV and Implications for Direct Photon Production

Journal Article · Fri Jan 01 04:00:00 EST 2010 · Physical Review C

DOI:https://doi.org/10.1103/PhysRevC.81.034911· OSTI ID:974638

Adare, A. ^[1]; Awes, Terry C ^[2]; Cianciolo, Vince ^[2]; Efremenko, Yuri ^[3]; Enokizono, Akitomo ^[4]; Read, Jr, Kenneth F ^[2]; Silvermyr, David O ^[2]; Sorensen, Soren P ^[5]; Stankus, Paul W ^[2]; Young, Glenn R ^[2]

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1. University of Colorado, Boulder
2. ORNL
3. University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL)
4. Oak Ridge National Laboratory (ORNL)
5. University of Tennessee, Knoxville (UTK)

PHENIX has measured the e{sup +}e{sup -} pair continuum in {radical}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 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} = 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 T = 100 MeV. Theoretical models underpredict the low-mass, low-p{sub T} enhancement.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 974638
• Journal Information: Physical Review C, Journal Name: Physical Review C Journal Issue: 3 Vol. 81
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
MESONS
PHOTONS
PRODUCTION