Direct Photons at RHIC

Conference · Tue Jul 29 04:00:00 EDT 2008

OSTI ID:941623

Gabor, D

Direct photons are ideal tools to investigate kinematical and thermodynamical conditions of heavy ion collisions since they are emitted from all stages of the collision and once produced they leave the interaction region without further modification by the medium. The PHENIX experiment at RHIC has measured direct photon production in p+p and Au+Au collisions at 200 GeV over a wide transverse momentum (p{sub T}) range. The p+p measurements allow a fundamental test of QCD, and serve as a baseline when we try to disentangle more complex mechanisms producing high p{sub T} direct photons in Au+Au. As for thermal photons in Au+Au we overcome the difficulties due to the large background from hadronic decays by measuring 'almost real' virtual photons which appear as low invariant mass e{sup +}e{sup -} pairs: a significant excess of direct photons is measured above the above next-to-leading order perturbative quantum chromodynamics calculations. Additional insights on the origin of direct photons can be gained with the study of the azimuthal anisotropy which benefits from the increased statistics and reaction plane resolution achieved in RHIC Year-7 data.

• Research Organization: Brookhaven National Laboratory
• Sponsoring Organization: Doe - Office Of Science
• DOE Contract Number: AC02-98CH10886
• OSTI ID: 941623
• Report Number(s): BNL--81700-2008-CP; KB0201021
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
74 ATOMIC AND MOLECULAR PHYSICS
ANISOTROPY
HEAVY IONS
HIGH ENERGY PHYSICS
MODIFICATIONS
ORIGIN
PHOTONS
PRODUCTION
QUANTUM CHROMODYNAMICS
RESOLUTION
STATISTICS
TRANSVERSE MOMENTUM