Estimates of Electromagnetic Signals from Deconfined Matter Produced in Ultrarelativistic Heavy-Ion Collisions
Electromagnetic signals, i.e., real and virtual photons, have proven to be experimentally accessible probes of highly excited, strongly interacting matter in intermediate and relativistic heavy-ion collisions, both for Bevalac energies1 and for SPS energies.2 Indeed, at SPS in CERN the three large dilepton experiments, which measure the decay products of the virtual photons either as electron — positron pairs (CERES) or muon — anti-muon pairs (NA38, HELIOS-3), have detected an ‘excess’ of observed dileptons, i.e., a larger number of pairs in certain phase space regions than it could be explained by simple superpositions of known hadron decay sources or individual pp collisions. This is particularly tempting, since it indicates interesting features at nucleon — nucleon center-of-mass energies of GeV already for such light projectile — target combinations as S + S, S + U, and 0 + U.
KeywordsVirtual Photon Hadron Matter Transverse Expansion Confinement Transition Dilepton Spectrum
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