Speaker
Dr
Yorito Yamaguchi
(University of Tokyo)
Description
Direct photons in low pT region have been of great interest for a long time since thermal photons from Quark Gluon Plasma (QGP) are considered to contribute predominantly.
Attempts to measure low pT direct photons using EMCals could not succeed since a finite energy resolution of the EMCal prevents us from separating direct photon signal from a large amount of background of hadron decay photons, particularly pi0.
Recently, the PHENIX experiment demonstrated that direct photon yield can be obtained even in low pT region via the di-electron measurement since direct photon internal conversions make enhanced yield of di-electrons over the known hadron decay contributions.
Comparing direct photon yields in $\sqrt{s_{NN}}=200~$GeV p+p and Au+Au collisions, a significant excess over the binary scaled p+p result is seen in Au+Au for pT<3GeV/c.
However, it should be confirmed that the observed excess of direct photons is not due to nuclear effects such as Cronin effect, nuclear anti-shadowing and so on, since nuclear effects are involved in Au+Au collisions but not in p+p collisions.
d+Au collision data can contribute to quantify nuclear effects on direct photon production.
The latest results of low pT direct photons from d+Au data taken in the Year-2008 RHIC Run will be shown.
Primary author
Dr
Yorito Yamaguchi
(University of Tokyo)
