Photon Production in Hot and Dense Strongly Interacting Matter

Abstract

Summary. This text is meant as an introduction to the theoretical physics of photon emission in hot and dense strongly interacting matter, the principal application being relativistic nuclear collisions. We shall cover some of the results and techniques appropriate for studies at SPS, RHIC, and LHC energies.

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

“…All the photons radiated during the matter evolution are usually divided into decay photons, i.e., those coming from hadron decays (e.g., from π 0 , ω, and η meson decays) [12], and direct photons, including all the other photons apart from the decay ones. The direct photons, in turn, are subdivided into prompt photons, i.e., the photons emitted at the very initial stage of the two nuclei collision as a result of hard partonic scatterings and jet fragmentations, pre-equilibrium photons, coming from the hot guark-gluon matter at the early stage of its evolution, while it has not yet reached a nearly thermal and locallyequilibrated state (this includes also the glasma phase [13][14][15][16][17]), and thermal photons, emitted from the expanding nearly thermalized continuous Quark-Gluon medium [18], as well as from the hadron-resonance gas formed at the late stage of the collision, when continuous QGP gets finally transformed into particles [19]. One can also consider such direct photon sources as jet-photon conversion and jet-induced bremsstrahlung [20,21], involving the interaction of hard partons with the thermal QGP medium.…”

Thermal photon emission from the πρω system

“…They thus encode information on properties of the fireball which are not easily accessible otherwise, e.g., on its interior temperatures, the total space-time volume, and evolution history of its collective properties (see, e.g., the reviews in Refs. [5][6][7] for further information on the role of EM probes in URHICs).…”

Probing Early-Time Dynamics and Quark-Gluon Plasma Transport Properties with Photons and Hadrons

“…We now turn to a discussion on photon production. Owing to the relative size of the electromagnetic fine structure constant compared to its strong interaction counterpart, electromagnetic radiation will escape the medium upon creation and will reflect all epochs of the collision process [11,12]. Traditionally, the vast majority of photon calculations account for the radiation from the very first nucleon-nucleon collisions and for that emitted throughout the fluid dynamical evolution [13].…”