Radial flow from electromagnetic probes and signal of quark gluon plasma

Abstract

An attempt has been made to extract the evolution of radial flow from the analysis of the experimental data on electromagnetic probes measured at the energies available at the CERN Super Proton Synchrotron (SPS) and the BNL Relativistic Heavy Ion Collider (RHIC). The transverse momentum (${p}_{T}$) spectra of photons and dileptons measured by the WA98 and NA60 Collaborations, respectively, at the SPS and the photon and dilepton spectra obtained by the PHENIX Collaboration at the RHIC have been used to constrain the theoretical models. We use the ratio of photon to dilepton spectra to extract the flow, where some model dependence is canceled out. Within the ambit of the present analysis we argue that the variation of the radial velocity with invariant mass is indicative of a phase transition from the initially produced partons to hadrons at SPS and RHIC energies.