Thermal Photons and Lepton Pairs from Quark Gluon Plasma and Hot Hadronic Matter

Abstract

The formulation of the real and virtual photon production rate from strongly interacting matter is presented in the framework of finite temperature field theory. The changes in the hadronic spectral function induced by temperature are discussed within the ambit of the Walecka type model, gauged linear and non-linear sigma models, hidden local symmetry approach, and QCD sum rule approach. The possibility of observing the direct thermal photon and lepton pairs from quark gluon plasma has been contrasted with those from hot hadronic matter with and without medium effects for various mass variation scenarios. At SPS energies, in-medium effects of different magnitude on the hadronic properties for the Walecka model, Brown–Rho scaling, and Nambu scaling scenarios are conspicuously visible through the low invariant mass distribution of dileptons and transverse momentum spectra of photons. However, at RHIC energies the thermal photon (dilepton) spectra originating from quark gluon plasma overshines those from hadronic matter for large transverse momentum (invariant mass) irrespective of the models used for evaluating the finite temperature effects on the hadronic properties. It is thus expected that at both RHIC and LHC energies the formation of quark gluon plasma in the initial stages may indeed turn out to be a realistic scenario.