Enhanced Production of Direct Photons in Au+Au Collisions at s_NN = 200 GeV and Implications for the Initial Temperature

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

DOI:https://doi.org/10.1103/PhysRevLett.104.132301· OSTI ID:976018

Adare, A. ^[1]; Awes, Terry C ^[2]; Cianciolo, Vince ^[2]; Efremenko, Yuri ^[3]; Read, Jr, Kenneth F ^[2]; Silvermyr, David O ^[2]; Sorensen, Soren P ^[4]; 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. University of Tennessee, Knoxville (UTK)

The production of e{sup +}e{sup -} pairs for m{sub e{sup +}e{sup -}} < 0.3 GeV/c{sup 2} and 1 < p{sub T} < 5 GeV/c is measured in p+p and Au+Au collisions at {radical}s{sub NN} = 200 GeV. An enhanced yield above hadronic sources is observed. Treating the excess as photon internal conversions, the invariant yield of direct photons is deduced. In central Au+Au collisions, the excess of the direct photon yield over p+p is exponential in transverse momentum, with an 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 {approx} 0.6-0.15 fm/c after the collision are in qualitative agreement with the data. Lattice QCD predicts a phase transition to quark gluon plasma at {approx} 170 MeV.

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 976018
• Journal Information: Physical Review Letters, Journal Name: Physical Review Letters Journal Issue: 13 Vol. 104; ISSN 0031-9007; ISSN PRLTAO
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
INTERNAL CONVERSION
PHOTONS
PRODUCTION
QUANTUM CHROMODYNAMICS
QUARK MATTER
TRANSVERSE MOMENTUM