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

Journal Article · Fri Apr 02 04:00:00 EDT 2010 · Physical Review Letters

DOI:https://doi.org/10.1103/PhysRevLett.104.132301· OSTI ID:1040383

Adare, A d

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} {approx} 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: Brookhaven National Laboratory (BNL) Relativistic Heavy Ion Collider
• Sponsoring Organization: USDOE SC OFFICE OF SCIENCE (SC)
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 1040383
• Report Number(s): BNL--91231-2010-JA; KB0201021
• 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
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
INTERNAL CONVERSION
PHOTONS
PRODUCTION
QUANTUM CHROMODYNAMICS
QUARK MATTER
TRANSVERSE MOMENTUM
relativistic heavy ion collider