Radiative hadronization: Photon emission at hadronization from quark-gluon plasma

TL;DR

This paper proposes a radiative hadronization mechanism where photon emission occurs during quark-antiquark recombination into mesons in quark-gluon plasma, predicting enhanced photon yield and flow consistent with heavy-ion collision data.

Contribution

It introduces a novel radiative hadronization model that incorporates photon emission during recombination, extending existing hadronization frameworks.

Findings

Enhanced photon yield due to radiative hadronization

Photon flow similar to hadron flow observed

Photon $p_T$ distribution exhibits a thermal profile with blue-shifted temperature

Abstract

We investigate photon emission at the hadronization stage from a quark-gluon plasma created in relativistic heavy-ion collisions. A recombination-model picture suggests that a quark and an antiquark bind into a meson state in hadronization, which would apparently violate the energy conservation if there is nothing else involved. We consider here a hadronization process where the recombination accompanies a photon emission. This is an analog of the "{\it radiative recombination}" known in plasma physics, such as $e^- + p^+ \to {\rm H}^0 +\gamma$, which occurs when an electromagnetic plasma goes back to a neutral atomic gas. The "radiative hadronization" picture will bring about (i) an enhancement of the photon yield, (ii) significant flow of photons similar to that of hadrons, and (iii) the photon transverse momentum ($p_T$) distribution with a thermal profile whose effective temperature is given by blue-shifted temperature of quarks. Here as a simplest and phenomenological realization of the radiative hadronization, we modify the recombination model to involve a photon emission and evaluate the photon yield with this modified model. Adding this contribution to the direct photon yield along with thermal photon contribution calculated with a hydrodynamic model and a parametrized contribution of prompt photons, we study the $p_T$ spectrum and elliptic flow of the photons produced in heavy-ion collisions at RHIC and LHC energies.