Probing collectivity in ultra-relativistic heavy ion collision by leptons and photons

It has been shown that the evolution of collectivity in ultra-relativistic heavy ion collision is manifested in the variation of various HBT radii with invariant mass (M) extracted from the correlation functions of two lepton pairs. The value of the radial velocity (image) can be estimated from the ratio of the image distributions of single photons to lepton pairs for various M windows. It has been argued that the variation of radial flow with appropriate kinematic variables can be used as an indicator of a phase transition from initially produced partons to hadrons. We also consider the elliptic flow (image) of the matter as probed by the single electron spectra originating from the semileptonic decays of heavy mesons. The measured values of image and the nuclear suppression factor (image) at RHIC energy have been reproduced simultaneously by including both the collisional and radiative processes within the scope of perturbative quantum chromodynamics. The image and image have been predicted for LHC energy.