Dileptons and Direct Photons at SPS

Abstract

The study of dilepton and direct photon emission was one of the main topics of the experimental program at the SPS devoted to the search of signals for QGP formation. Three generations of experiments, Helios-3, NA38/NA50, CERES and NA60 measured e+e- or mu+mu- production in various colliding systems and at different energies. While lepton pair production in p-A collisions was found to be reasonably well described by the expected sources, all experiments observed in nuclear collisions an excess of the yield above the extrapolation from p-A. As a result of this joint experimental effort we have currently a large amount of information characterizing this excess: its mass spectrum over the full range from 0.2 GeV/c^2 up to the J/psi, its transverse momentum spectra including their mass dependence, its angular distributions, its dependence on collision centrality over the complete range etc. Putting together all this information leads to the conclusion that what we observe is the long-sought thermal radiation from the fireball.

8 pages, 6 figures - To appear in the conference proceedings for Quark Matter 2009, March 30 - April 4, Knoxville, Tennessee

References in corpus (12)

• Dilepton Radiation at the CERN Super Proton Synchrotron
• Study of the electromagnetic transition form-factors in η-> μ^+μ^-γand ω-> μ^+μ^-π^0 decays with NA60
• Evidence for the production of thermal muon pairs with masses above 1 GeV/c^2 in 158A GeV Indium-Indium Collisions
• NA60 results on thermal dimuons
• Evidence for radial flow of thermal dileptons in high-energy nuclear collisions
• Low Mass Dimuons Produced in Relativistic Nuclear Collisions
• Thermal Dimuon Yields at NA60
• Dimuon transverse momentum spectra as a tool to characterize the emission region in heavy-ion collisions
• First measurement of the rho spectral function in nuclear collisions
• Thermal dileptons at SPS energies
• First results on angular distributions of thermal dileptons in nuclear collisions
• $\varphi$ Production in In-In Collisions at 158 AGeV