Title: Centrality-dependent direct photon<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mi>p</mml:mi><mml:mrow><mml:mi>t</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>spectra in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Au</mml:mi><mml:mo>+</mml:mo><mml:mi mathvariant="normal">Au</mml:mi></mml:mrow></mml:math>collisions at the BNL Relativistic Heavy Ion Collider (RHIC) energy…
Abstract: We calculate the centrality dependence of transverse momentum $({p}_{t})$ spectra for direct photons in $\mathrm{Au}+\mathrm{Au}$ collisions at the BNL Relativistic Heavy Ion Collider (RHIC) energy $\sqrt{{s}_{\mathit{NN}}}=200 \mathrm{GeV}$, based on a realistic data-constrained $(3+1)$-dimensional hydrodynamic description of the expanding hot and dense matter, a reasonable treatment of the propagation of partons and their energy loss in the fluid, and a systematic study of the main sources of direct photons. The resultant ${p}_{t}$ spectra agree with recent PHENIX data in a broad ${p}_{t}$ range. The competition among the different direct photon sources is investigated at various centralities. Parton energy loss in the plasma is considered for photons from fragmentation and jet-photon conversion, which causes about 40% decrease in the total contribution. In the high ${p}_{t}$ region, the observed ${R}_{\mathit{AA}}$ of photons is centrality independent at the accuracy of 5% based on a realistic treatment of energy loss. We also link the different behavior of ${R}_{\mathit{AA}}$ for central and peripheral collisions, in the low ${p}_{t}$ region, to the fact that the plasma in central collisions is hotter than that in peripheral ones.