Direct Photon Production in High-Energy Heavy Ion Collisions within the Integrated Hydrokinetic Model

Yuri Sinyukov,Volodymyr Shapoval

doi:10.3390/j5010001

Abstract

The results on description of direct photon yields, transverse momentum spectra, and flow harmonics, measured in ultrarelativistic heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) for different collision centrality classes, analyzed within the Integrated Hydrokinetic Model (iHKM) are reviewed. The iHKM simulation results, corresponding to the two opposite approaches to the matter evolution treatment at the final stage of the system’s expansion within the model, namely, the chemically equilibrated and the chemically frozen evolution, are compared. The so-called “direct photon puzzle” is addressed, and its possible solution, suggesting the account for additional photon emission at confinement, is considered.

Highlights

In the papers [45,46] to describe the photon production at Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) we utilized the same model parameters tuning which previously ensured the successful description of hadron observables at the same collision energies [5,6]
As a result of analysis carried out in [45,46] it was found that the description of direct-photon p T spectra, elliptic and triangular flow p T -dependencies, v2 ( p T ) and v3 ( p T ), can be significantly improved, for both RHIC and the LHC energies, if one includes, along with the contributions from prompt, pre-thermal and thermal (QGP and hadron gas) photon emission, an additional portion of γ radiation, corresponding to the confinement process, which can be called the “hadronization photons” (see Figure 1, demonstrating the RHIC and the LHC photon spectra calculated within the Integrated Hydrokinetic Model (iHKM) for the central events (c = 0–20%); the spectra obtained with and without accounting for the hadronization emission (HE) are shown)
In order to fix the value of the β parameter, one should at first perform fitting of the direct-photon spectrum for the case of most central events

Summary

Introduction

High-Energy Heavy Ion Collisions within the Integrated Hydrokinetic. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations

Objectives

Results

Conclusion