Radiation of single photons from $Pb+Pb$ collisions at the CERN SPS and quark hadron phase transition

Abstract

The production of single photons in $Pb+Pb$ collisions at the CERN SPS as measured by the WA98 experiment is analysed. A quark gluon plasma is assumed to be formed initially, which expands, cools, hadronizes, and undergoes freeze-out. A rich hadronic equation of state is used and the transverse expansion of the interacting system is taken into account. The recent estimates of photon production in quark-matter (at two loop level) along with the dominant reactions in the hadronic matter leading to photons are used. About 50% of the single photons are seen to have a thermal origin. An addition of the thermal and prompt photons is seen to provide a very good description of the data. Most of the thermal photons having large transverse momenta arise from the quark-matter, which contributes dominantly through the mechanism of annihilation of quarks with scattering, and which in turn is possible only in a hot and dense plasma of quarks and gluons. The results thus confirm the formation of quark gluon plasma and the existence of this mechanism of the production of single photons.

6 pages including 3 figures. Corrected 2-loop rates for photons are used

References in corpus (3)

• Observation of Direct Photons in Central 158 A GeV 208Pb+208Pb Collisions
• Photons from Pb-Pb Collisions at CERN SPS
• A unique large thermal source of real and virtual photons in the reactions Pb(158 AGeV) + Pb, Au

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