Photon elliptic flow in relativistic heavy-ion collisions: hadronic versus partonic sources

Abstract

We study the transverse momentum spectrum and the elliptic flow v2 of photons produced in Au+Au collisions at sqrt(s)=200 GeV using the Parton-Hadron-String Dynamics (PHSD) transport approach. As sources for photon production, we incorporate the interactions of off-shell quarks and gluons in the strongly interacting quark-gluon plasma (q+qbar->g+gamma and q/qbar+g->q/qbar+gamma), the decays of hadrons (pi->gamma+gamma, eta->gamma+gamma, omega->pi+gamma, eta'->rho+gamma, phi->eta+gamma, a_1->pi+gamma) as well as their interactions (pi+pi->rho+gamma, rho+pi->pi+gamma, bremsstrahlung m+m->m+m+gamma). The PHSD calculations reproduce the transverse momentum spectrum, the effective temperature T_eff and the elliptic flow v2 of both inclusive and direct photons as measured by the PHENIX Collaboration. The photons produced in the QGP contribute slightly less then 50% to the observed spectrum, but have small v2. We find that the large direct photon v2 - comparable to that of hadrons - can be attributed to the intermediate hadronic scattering channels not subtracted from the data when following the same extraction procedure for v2 as in the PHENIX experiment. On the other hand the v2 of direct photons - as evaluated by the weighted average of direct photon channels - gives a lower signal. The difference between the two extraction procedures for the direct photon v2 can be attributed to different definitions for the yield ratio of direct photons to the background photons. The QGP phase causes the strong elliptic flow of photons indirectly, by enhancing the v2 of final hadrons due to the partonic interaction in terms of explicit parton collisions and the mean-field potentials. We also show that the presence of the QGP radiation is manifest in the slope of the direct photon spectrum, leading to a slope parameter T_eff far above the critical temperature for the deconfinement phase transition.

12 pages, 13 figures, section on the direct photon v2 extended, conclusions unchanged

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Cited by in corpus (35)

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• Centrality dependence of the direct photon yield and elliptic flow in heavy-ion collisions at sqrt(s)=200 GeV
• Hadronic and partonic sources of direct photons in relativistic heavy-ion collisions
• Direct real photons in relativistic heavy ion collisions
• Chiral symmetry restoration in heavy-ion collisions at intermediate energies
• The Glasma, Photons and the Implications of Anisotropy
• Chiral symmetry restoration versus deconfinement in heavy-ion collisions at high baryon density
• Electric and magnetic response of hot QCD matter
• Thermal photon $v_2$ with slow quark chemical equilibration
• Charge-dependent directed flow in asymmetric nuclear collisions
• Thermal photon radiation in high multiplicity p+Pb collisions at the Large Hadron Collider
• Photon production from a non-equilibrium quark-gluon plasma
• A Tale of Tails: Photon Rates and Flow in Ultra-Relativistic Heavy Ion Collisions
• Impact of the initial size of spatial fluctuations on the collective flow in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV
• Phenomenology of photon and di-lepton production in relativistic nuclear collisions
• Observables in ultrarelativistic heavy-ion collisions from two different transport approaches for the same initial conditions
• Properties of the QGP created in heavy-ion collisions
• Traces of non-equilibrium effects, initial condition, bulk dynamics and elementary collisions in the charm observables
• High-energy $\pi \pi$ scattering without and with photon radiation
• Photon production from Pb+Pb collisions at {$\sqrt{s_{\mathrm{NN}}}$} = 5.02 TeV at LHC and at {$\sqrt{s_{\mathrm{NN}}}$} = 39 TeV at FCC
• Baryon-antibaryon dynamics in relativistic heavy-ion collisions
• Chiral symmetry breaking and confinement effects on dilepton and photon production around $T_c$
• Electromagnetic fingerprints of the Little Bang
• Effective distributions of quasi-particles for thermal photons
• What are the early degrees of freedom in ultra-relativistic nucleus-nucleus collisions?
• Photons production in heavy-ion collisions as a signal of deconfinement phase
• Probing confinement by direct photons and dileptons
• Anisotropy of thermal dileptons
• Dynamics of strongly interacting parton-hadron matter
• Finite-Density Dynamics of Chemically Equilibrating QGP in Conformal Gubser Flow and Hard Thermal Photon Production
• Charged particle to photon ratio in heavy-ion collisions at RHIC: a different point of view
• Emissivity and conductivity of parton-hadron matter