1202.3844 (Ranbir Singh et al.)

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

Ranbir Singh, Md. Nasim, Bedangadas Mohanty, Sanjeev Singh Sambyal

We present a comparison of inclusive photon elliptic flow parameter (v_{2})
measured at RHIC and SPS high energy heavy-ion collision experiments to
calculations done using the AMPT and UrQMD models. The new results discussed
includes the comparison of the model calculations of photon v_{2} 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 < \eta < 3.9) at RHIC as was previously observed for
measurements at midrapidity. At the top SPS energy the contribution from
partonic effects are smaller than that at RHIC energy, based on the comparison
of the measured photon v_{2} 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 v_{2} at top RHIC
energies (19.6-200 GeV) will be violated. We also discuss the relation between
the inclusive photon v_{2} and those of their parent \pi^{0}'s for the beam
energies of 7.7 GeV to 2.76 TeV. The model results show that the transverse
momentum (p_{\mathrm T}) integrated v_{2} of \pi^{0} is larger by about 44%
relative to those of the inclusive photons. Finally we present the expectations
of inclusive photon v_{2} for the RHIC beam energy scan (BES) program and LHC
from the transport models, so that they can be compared to corresponding
measurements using the data already collected at RHIC and LHC.

View original: http://arxiv.org/abs/1202.3844