Untangling the evolution of heavy ion collisions using direct photon interferometry

Abstract

Recently, two scenarios have been proposed to resolve the discrepancy between photon yield and the flow coefficients measured in nuclear collisions at RHIC and the LHC. In the first, additional photons are produced from the early pre-equilibrium stage computed from the "bottom-up" thermalization scenario. In the second, the thermal rates are enhanced close to the pseudo-critical temperature $T_c \sim$ 155MeV using a phenomenological ansatz. We investigate the measurement of Hanbury Brown-Twiss (HBT) photon correlations as an experimental tool to discriminate between such scenarios. By enhancing standard hydrodynamical simulations with these scenarios, we compute the correlators in terms of the relative momenta of the pair for different values of its transverse momenta, $K_\perp$ We find that the longitudinal correlation is the most sensitive to different photon sources.