Neutral pion production with respect to centrality and reaction plane in Au$+$Au collisions at $\sqrt{s_{NN}}$=200 GeV

The PHENIX collaboration
Phys.Rev.C 87 (2013) 034911, 2013.

Abstract (data abstract)
BNL-RHIC. The PHENIX experiment has measured the production of neutral pions in Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV. The new data offer a fourfold increase in recorded luminosity, providing higher precision and a larger reach in transverse momentum, $p_T$, to 20 GeV/c. The production ratio of $\eta/\pi^0$ is 0.46$\pm$0.01(stat)$\pm$0.05(syst), constant with $p_T$ and collision centrality. The observed ratio is consistent with earlier measurements, as well as with the p+p and d+Au values. The production of $\pi^0$ is suppressed by a factor of 5, as in earlier findings. However, with the improved statistical precision a small but significant rise of the nuclear modification factor, $R_{AA}$, vs $p_T$, with a slope of 0.0106$^(+0.0034)_(-0.0029)[GeV/c]^-1$, is discernible in central collisions. A phenomenological extraction of the average fractional parton energy loss shows a decrease with increasing $p_T$. To study the path length dependence of suppression, the $\pi^0$ yield was measured at different angles with respect to the event plane; a strong azimuthal dependence of the $\pi^0 R_{AA}$ is observed. The data are compared to theoretical models of parton energy loss as a function of the path length, L, in the medium. Models based on pQCD are insufficient to describe the data, while a hybrid model utilizing pQCD for the hard interactions and AdS/CFT for the soft interactions is consistent with the data.

  • Figure 5


    Invariant yields of neutral pions, all centralities

  • Figure 8


    $\Eta/ \pi^0 ratios

  • Figure 11


    $\pi^0$ nuclear modification factors

  • Figure 20-1


    $pi^0$ nuclear modification factors vs reaction plane, $\Delta \phi = 0^{\circ}-15^{\circ}$

  • Figure 20-2


    $pi^0$ nuclear modification factors vs reaction plane, $\Delta \phi = 15^{\circ}-30^{\circ}$

  • Figure 20-3


    $pi^0$ nuclear modification factors vs reaction plane, $\Delta \phi = 30^{\circ}-45^{\circ}$

  • Figure 20-4


    $pi^0$ nuclear modification factors vs reaction plane, $\Delta \phi = 45^{\circ}-60^{\circ}$

  • Figure 20-5


    $pi^0$ nuclear modification factors vs reaction plane, $\Delta \phi = 60^{\circ}-75^{\circ}$

  • Figure 20-6


    $pi^0$ nuclear modification factors vs reaction plane, $\Delta \phi = 75^{\circ}-90^{\circ}$

  • Figure 21


    Centrality dependence of $p_T$ ingetrated $R_{AA}(\Delta \phi)$

Version 2 modifications: Revised abstract to remove LaTeC math inconsitency

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