Measurements by the PHENIX collaboration revealed that the anisotropy of produced photons is very close to that of hadrons at sqrt(s) =200 GeV . Very recent data from the ALICE collaboration at the LHC affirms this at significantly higher collision energies. These results contradict the current theory of photon production: It has been expected that the elliptic flow of direct photons would be much smaller than that of hadrons because a significant fraction of photons has to be produced at early times, when the temperature is the highest.
In this talk, I will discuss the novel photon production mechanism stemming from the conformal anomaly of QCD+QED and the existence of strong (electro)magnetic field in heavy-ion collisions. Using a realistic input for the magnetic field and the hydrodynamical description of the bulk modes of QCD plasma, I show that this mechanism leads to the photon production yield that is comparable to the yield from conventional sources. The transverse momentum spectra and the anisotropy (the elliptic “flow”), of photons at sqrt(s) =200 GeV are calculated. This mechanism provides considerable contribution to the anisotropy of photons. The results will be compared to the data from the PHENIX collaboration.
Based on http://arxiv.org/abs/arXiv:1206.1334