Electromagnetic probes of quark gluon plasma

We consider boost invariant longitudinal flow and try to understand the contemporary scenario with a typical space time evolution going over from QGP to a mixed phase of hadrons and QGP and then on to a free streaming non interacting hadrons going over to the detector after the hadrons have frozen to a non interacting system. Two scenarios are considered for searching quark gluon plasma: (a) Nucleus + Nucleus → Hadrons -> γ's, leptons, hadrons, etc; (b) Nucleus + Nucleus -> QGP -> Hadrons -> γ's, leptons, hadrons, etc. In the case (a) it is assumed that the matter is formed in the hadronic phase initially after the nucleus nucleus collisions (no phase transition scenario). It maintains thermal equilibrium up to a temperature Tf(= 140 MeV), after which it freezes out and detected experimentally. Whereas in case (b) a QGP is assumed to be formed, it cools due to expansion, goes over to the mixed phase in a first order phase transition scenario when temperature is reduced to Tc(=160 MeV). When all the latent heat is liberated, the system goes to the pure hadronic phase in the usual fashion. In the case (a) we have assumed an equation of state (EOS) which is consistent with π, ρ, ω and η in the hadronic phase. In the scenario (b) we assume that at the initial time τi = 1 fm/c the two flavours u and d, their anti quarks and the gluons are thermalized. For dileptons emission from QGP we consider the annihilation contribution (q q-bar -> l l-bar). For the hadronic matter we consider all possible reactions of the type V + P -> l l-bar, P + P -> l l-bar and V + V -> l l-bar. The dilepton transverse mass spectrum is obtained by convoluting the rates for the emission of dileptons from the QGP. Results are presented for thermal dileptons after incorporating the cuts as for the CERES detector. It is also presented the contribution of the QGP phase, the QGP part of the mixed phase, the hadronic part of the mixed phase, and the hadronic phase separately