Electromagnetic Probes: Theory and Experiment

Abstract

We review the current state of research on electromagnetic probes in the context of heavy-ion collisions. The focus is on thermal photons and dileptons which provide unique insights into the properties of the created hot and dense matter.This review is intended to provide an introductory overview of the topic as well as a discussion of recent theoretical and experimental results. In particular, we discuss the role of vector-meson spectral functions in the calculation of photon and dilepton rates and present recent results obtained from different frameworks. Furthermore, we will highlight the special role of photons and dileptons to provide information on observables such as the temperature, the lifetime, the polarization and the electrical conductivity of the produced medium as well as their use to learn about chiral symmetry restoration and phase transitions.

Baryon-rich QCD matter

“…A preliminary estimate for the thermal dielectron rate, dN e + e − /d 4 xd 4 q, near the chiral CEP, using the ρmeson SpF in the right panel of Fig. 4 has been obtained in [38] and the result is displayed in Fig. 5.…”

Electric conductivity of hot pion matter

“…In particular, we will take advantage of the close relation of σ el to the thermal dilepton emission rate [1], as both quantities are directly proportional to the electromagnetic spectral function of the strongly interacting medium. On the one hand, this allows to establish connections between the processes that are widely implemented to describe low-mass dilepton and photon radiation observed in experiments at the SPS, RHIC, HADES and the LHC [2][3][4]. On the other hand, renewed interest in the conductivity has recently been triggered by future plans to access the pertinent transport peak more directly in experiment through very low-mass and lowmomentum dileptons, as being envisaged at the Schwer-Ionen Synchrotron (SIS), the Relativistuc Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC) [5][6][7].…”