Centrality dependence of the direct photon yield and elliptic flow in heavy-ion collisions at sqrt(s)=200 GeV

Understand

We calculate the centrality dependence of direct photons produced in Au+Au collisions at sqrt{s}=200GeV and their transverse momentum spectra within the Parton-Hadron-String Dynamics (PHSD) transport approach.

• As sources for 'direct' photons, we incorporate the interactions of quarks and gluons as well as hadronic interactions (pi+pi->rho+gamma, rho+pi->pi+gamma, meson-meson bremsstrahlung m+m->m+m+gamma, meson-baryon bremsstrahlung m+B->m+B+gamma), the decays of phi and a_1 mesons and the photons produced in the initial hard collisions ('pQCD').
• We find that the pT spectra of the 'thermal' photons (i.e.
• the direct photons after the pQCD contribution is subtracted) deviate from exponential distributions and, consequently, observe a strong dependence of the inverse slope parameter T_eff on the fitting range in pT.