Electromagnetic Radiation at RHIC

Electromagnetic radiation from nuclear collisions at RHIC energies

Dileptons and direct photons can carry information on the thermodynamic state of the deconfined medium at the moment of production – since they interact only electromagnetically they can leave the hot and dense reaction zone basically undistorted, making them valuable and direct probes of the intermediate QGP phase of the heavy-ion reaction. However, photons can be emitted via many different mechanisms and during the entire time-evolution of the heavy-ion reaction, making the interpretation of the measured photon spectrum inherently difficult. This paper represents a good snapshot of the current state of the art and shows how many different photon sources need to be taken into account to provide a description of the data. It demonstrates the tremendous attention to detail required in this area of research and that strong improvements on the side of the data at lower p_T (between 0.5 and 3 GeV/c) are needed in order to isolate the much sought after signal of thermal QGP radiation.

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