Electromagnetic signals from Au + Au collisions at RHIC energy, sNN=200 GeV and Pb + Pb collisions at LHC energy, sNN=2.76 TeV

We analyse the recently available experimental data on direct photon productions from Au + Au collisions at sNN=200 GeV RHIC and from Pb + Pb collisions at sNN=2.76 TeV LHC energies. The transverse momentum (pT) distributions have been evaluated with the assumption of an initial quark gluon plasma phase at energy densities ϵi=41 and 70 GeV/fm3 with initial thermalisation times τi=0.2 and 1.0 fm/c respectively for RHIC and LHC energies. The theoretical evaluations agree well with the experimental observations. The thermal radiations dominate within the pT range 1.5⩽pT(GeV)⩽3.5. The ratio of thermal photons to dileptons (Rem=[d2Nγ/d2pTdy]/[d2Nγ⁎/d2pTdy]) determines more precisely the window, as mentioned above.