Elliptic flow of thermal photons in Au plus Au collisions at √sNN=200 GeV

The transverse momentum (p(t)) dependence, the centrality dependence, and the rapidity dependence of the elliptic flow of thermal photons in Au + Au collisions at root s(NN) = 200 GeV are predicted on the basis of a three-dimensional ideal hydrodynamic description of the hot and dense matter. The elliptic flow parameter nu(2), i.e., the second Fourier coefficient of azimuthal distribution, of thermal photons first increases with p(t) and then decreases for p(t) > 2 GeV/c, because of the weak transverse flow at the early stage. The p(t)-integrated nu(2) first increases with centrality, reaches a maximum at about 50% centrality, and then decreases. The rapidity dependence of the elliptic flow nu(2)(y) of direct photons ( mainly thermal photons) is very sensitive to the initial energy density distribution along the longitudinal direction, which provides a useful tool to extract the realistic initial condition from measurements.