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 √{s_NN} = 200 GeV RHIC and from Pb + Pb collisions at √{s_NN} = 2.76 TeV LHC energies. The transverse momentum (p_T) distributions have been evaluated with the assumption of an initial quark gluon plasma phase at energy densities ɛ_i = 41 and 70 GeV/fm³ with initial thermalisation times τ_i = 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 p_T range 1.5 ⩽p_T (GeV) ⩽ 3.5. The ratio of thermal photons to dileptons (R_em = [d²N_γ /d²p_T dy ] / [d²N_γ^* /d²p_T dy ]) determines more precisely the window, as mentioned above.