Energy dependence of inclusive photon elliptic flow in heavy-ion collision models

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We present a comparison of inclusive photon elliptic flow parameter (v2) measured at the RHIC and super proton synchrotron (SPS) high-energy heavy-ion collision experiments to calculations performed using the multi-phase transport (AMPT) and ultra-relativistic quantum molecular dynamics (UrQMD) models. The new results discussed include the comparison of the model calculations of photon v2 to corresponding measurements at the forward rapidities. We observe that the AMPT model, which includes partonic interactions and quark coalescence as a mechanism of hadronization, is in good agreement with the measurements even at forward rapidities (2.3 < η < 3.9) at the RHIC, as was previously observed for measurements at midrapidity. At the top SPS energy, the contribution from partonic effects is smaller than that at RHIC energy, based on the comparison of the measured photon v2 with those from the AMPT default and UrQMD model calculations. We find that if the measurements in RHIC beam energy scan (BES) and LHC energies would require an energy-dependent partonic cross section in the AMPT models, then the observed longitudinal scaling of v2 at top RHIC energies (19.6–200 GeV) will be violated. We also discuss the relation between the inclusive photon v2 and those of their parent π0 for the beam energies of 7.7 GeV to 2.76 TeV. The model results show that the transverse momentum (pT) integrated v2 of π0 is relatively larger by about 44% than those of the inclusive photons. Finally, we present the expectations of inclusive photon v2 for the RHIC BES program and LHC from the transport models, so that they can be compared to corresponding measurements using the data already collected at the RHIC and LHC.