Single photons from Pb+Pb collisions at CERN SPS, QGP vs. hadronic gas

Abstract

In a hydrodynamic model, we have analysed the direct photon data obtained by the WA98 collaboration in 158 A GeV Pb+Pb collisions at CERN SPS. The transverse expansion of the system was taken into account. Two scenarios (i) formation of quark-gluon plasma and (ii) formation of hot hadronic gas were considered. Equally well description to the data were obtained in both the scenarios. However, hadronic gas scenario require very high initial temperature ($\sim$ 300 MeV) and it is difficult to conceive existence of hadron gas at that high temperature. If the hadronic fluid has small radial velocity (0.2c-0.3c) initially, the data are well explained in the hadronic gas scenario with reasonable initial temperatures.

5 pages including 4 figures, note: Revised version, Photon rates calculated by Aurenche et al are corrected for the factor of 4. Discussion on hard QCD photons are added

References in corpus (3)

• Particle Ratios, Equilibration, and the QCD Phase Boundary
• Photon emission in heavy ion collisions at the CERN SPS
• Emission of single photons, hadrons, and dileptons in $Pb+Pb$ collisions at CERN SPS and quark hadron phase transition

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• Photon tagged correlations in heavy ion collisions
• Exploring the QCD landscape with high-energy nuclear collisions