Paper detail

Direct photon observables from hydrodynamics and implications on the initial temperature and EoS

The expansion of the strongly interacting quark gluon plasma (sQGP) created in Au+Au collisions at RHIC can be described by hydrodynamical models. Hadrons are created after a freeze-out, thus their distribution describes the final state of the evolution. The earlier stages can be analyzed via penetrating probes like photon observables. These were measured in 2010 and 2011 by the PHENIX experiment. Here we analyze an analytic, 1+3 dimensional perfect relativistic hydrodynamic solution and calculate hadron and photon observables, such as transverse momentum spectra, elliptic flow and correlation (HBT) radii. We find that our model is not incompatible with the data, not even with the direct photon elliptic flow. From fitting the data, we find that early temperatures of the sQGP were well above the quark-hadron transition temperature, in the hottest point, the center of the fireball the temperature may have reached 507+-12 MeV. The equation of state of this quark matter can be described by an average sound speed of 0.36+-0.02. We also predict a photon source that is significantly larger in the out direction than in the side direction.