Photon spectra and anisotropic flow in heavy ion collisions at the top RHIC energy within the integrated hydrokinetic model with photon hadronization emission

TL;DR

This study uses the integrated HydroKinetic Model to analyze direct photon spectra and flow in RHIC heavy ion collisions, highlighting the importance of hadronization photons for accurate modeling.

Contribution

It introduces the inclusion of hadronization photon emission in the iHKM, improving the description of photon observables at RHIC energies.

Findings

Photon spectra and flow are better described with hadronization photons.

Centrality dependence of flow coefficients is captured by the model.

Inclusion of confinement-related radiation improves agreement with experimental data.

Abstract

The integrated HydroKinetic Model (iHKM) is applied to analyse the results of direct photon spectra as well as elliptic and triangular flow measurements in 200A GeV Au+Au collisions at RHIC for different centrality bins. Experiments detect the strong centrality dependence of photon elliptic and triangular flow as increasing $v_n(p_T)$-coefficients towards peripheral collisions. The photon production in the model is accumulated from the different sources along with the process of relativistic heavy ion collision developing. Those include the primary hard photons from the parton collisions at the very early stage of the process, the photons generated at the pre-thermal phase of dense matter evolution, then thermal photons at partially equilibrated hydrodynamic quark-gluon stage, together with radiation displaying a confinement and, finally, from the hadron gas phase. Along the way a hadronic medium evolution is treated in two distinct, in a sense opposite, approaches: chemically equilibrium and chemically non-equilibrium, namely, chemically frozen expansion. We find the description of direct photon spectra, elliptic and triangular flow are significantly improved, similar to that found in iHKM for the LHC energies, if an additional portion of photon radiation associated with the confinement processes, the "hadronization photons", is included into consideration.