Electromagnetic Probes of Strongly Interacting Matter
  Photons and dileptons are being used to probe the properties of nuclear and quark-gluon matter at high energy densities. This is an area where theory and experiment are driving each other to obtain solid results. However, it is important to clearly separate the assumptions and conclusions concerning the correlation and response functions of a system in thermal equilibrium from the space-time dynamics used to model the evolution of the matter created in the nuclear collision. 
J. Kapusta