Azimuthal flow of decay photons in relativistic nuclear collisions


An overwhelming fraction of photons from relativistic heavy ion collisions has its origin in the decay of Ο€0\pi^0 and Ξ·\eta mesons. We calculate the azimuthal asymmetry of the decay photons for several azimuthally asymmetric pion distributions. We find that the kTk_T dependence of the elliptic flow parameterv2v_2 for the decay photons closely follows the elliptic flow parameter v2Ο€0v_2^{\pi^0} evaluated at pTβ‰ˆkT+Ξ΄p_T \approx k_T+\delta, where Ξ΄β‰ˆ\delta\approx 0.1 -- 0.2 GeV, for typical pion distributions measured in nucleus-nucleus collisions at relativistic energies. Similar results are obtained for photons from the 2-Ξ³\gamma decay of Ξ·\eta mesons. Assuming that the flow of Ο€0\pi^0 is similar to those for Ο€+\pi^+ and Ο€βˆ’\pi^- for which independent measurements would be generally available, this ansatz can help in identifying additional sources for photons. Taken along with quark number scaling suggested by the recombination model, it may help to estimate v2v_2 of the parton distributions in terms of azimuthal asymmetry of the decay photons at large kTk_T.Comment: 6 pages, figures added, references added, with more elaborate discussion

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