Direct real photons in relativistic heavy ion collisions

Abstract

Direct real photons are arguably the most versatile tools to study relativistic heavy ion collisions. They are produced, by various mechanisms, during the entire space-time history of the strongly interacting system. Also, being colorless, most the time they escape without further interaction, ie they are penetrating probes. This makes them rich in information, but hard to decypher and interpret. This review presents the experimental and theoretical developments related to direct real photons since the 1970s, with a special emphasis on the recently emerged "direct photon puzzle", the simultaneous presence of large yields and strong azimuthal asymmetries of photons in heavy ion collisions, an observation that so far eluded full and coherent explanation.

Invited review paper, small updates, version accepted and published in Reports on Progress in Physics April 2020 (reformatted and with added biography), Rept.Prog.Phys. 83 (2020) 4, 046301

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Cited by in corpus (35)

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• Progress and Challenges in Small Systems
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