Direct photon production at RHIC and LHC energies

TL;DR

This paper investigates direct photon production and elliptic flow in heavy-ion collisions at RHIC and LHC energies using a relativistic transport model, highlighting the late-stage hadronic interactions' role in photon v2.

Contribution

It introduces a comprehensive transport approach (PHSD) to analyze direct photon spectra and flow, providing new insights into their origins and centrality dependence at high energies.

Findings

Large photon v2 signals significant late-stage hadronic contributions.

Predictions for LHC energies on photon spectra and v2 for 0-40% centrality.

Comparison with RHIC data supports the model's validity.

Abstract

Direct photon spectra and elliptic flow v2 in heavy-ion collisions at RHIC and LHC energies are investigated within a relativistic transport approach incorporating both hadronic and partonic phases - the Parton-Hadron-String Dynamics (PHSD). The results suggest that a large v2 of the direct photons - as observed by the PHENIX Collaboration - signals a significant contribution of photons produced in interactions of secondary mesons and baryons in the late stages of the collision. In order to further differentiate the origin of the direct photon azimuthal asymmetry, we compare our predictions for the centrality dependence of the direct photon yield to the recent measurements by the PHENIX Collaboration and provide predictions for Pb+Pb collisions at LHC energies with respect to the direct photon spectra and v2(pT) for 0-40% centrality.