Speaker
Dr
Edouard Kistenev
(Brookhaven National Laboratory)
Description
E.Kistenev for the PHENIX Collaboration
Direct photon production in heavy ion collisions in PHENIX experiment at RHIC
Among the observables used to probe the high temperature and high density phase of heavy nucleus collisions direct photons are considered of particular interest. At LO direct photons are produced in quark-gluon Compton scattering and quark-antiquark annihilation, the NLO processes are dominating in bremsstrahlung and fragmentation photon production and jet re-interaction in medium, QGP and hot hadronic stage emit thermal photons. Correlated measurements of the transverse momentum dependence of direct photon production in collisions of different species and of underlying event observables, like isolation or flow, as well as the nuclear modification factor may give insight into the relative contribution from various production mechanisms.
Extracting the direct photon signal from the large hadron decay background is experimentally challenging particularly at lower transverse momenta and high multiplicities. PHENIX used a combination of techniques based upon virtual (via low to intermediate mass e+e- pairs) and real (neutral clusters in calorimeters and reconstructed e+e- pairs from photon conversions) photon measurements to determine direct photon yields in the range of transverse momenta up to about 20 GeV/c for a wide range of energies and colliding species.
In this talk we present recent PHENIX results on total direct photon production in pp, dA and AA collisions with emphasis on azimuthal correlations and nuclear modification. Implications of the PHENIX measurements for the initial temperature and density estimates as well as for the space-time evolution of the fireball will also be discussed.
Primary author
Dr
Edouard Kistenev
(Brookhaven National Laboratory)
