Photon emission at hadronization

Abstract

We discuss photon emission at the stage of hadronization. We formulate it in accordance with the “radiative recombination,” such as e−+p+→H0+γ, which occurs when a plasma goes back to an atomic gas. The photon emission is essential to compensate the energy difference between the initial and final states. When a QGP hadronizes, we expect similar processes, such as q+q‾→π0+γ, to take place. However, since hadronization is a nonperturbative and nonequilibrium process, we need to resort to a certain phenomenological model at present. As such a model of hadronization, we employ the “recombination model” where hadrons are formed by coalescence of valence quarks. We improve this model so that the energy is conserved by the introduction of photon emission. This improved model, and thus our “radiative hadronization” picture has the following properties: (i) it brings about enhancement of the photon yield, (ii) radiated photons flow similarly as hadrons. and (iii) the pT distribution of emitted photons mimics thermal distribution whose effective temperature is given by blue-shifted quark's temperature. Within a simple setup, we present numerical results on the pT spectrum and elliptic flow parameter of the photon at RHIC and LHC energies.