Neutral pion production with respect to centrality and reaction plane in Au+Au collisions at s NN = 200 GeV

Le résumé fourni par la source

The PHENIX experiment has measured the production of ${\ensuremath{\pi}}^{0}$s in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{\mathit{NN}}}$ $=$ 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 $\ensuremath{\eta}/{\ensuremath{\pi}}^{0}$ is $0.46\ifmmode\pm\else\textpm\fi{}0.01(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.05(\mathrm{syst})$, constant with ${p}_{T}$ and collision centrality. The observed ratio is consistent with earlier measurements, as well as with the $p+p$ and $d+\mathrm{Au}$ values. ${\ensuremath{\pi}}^{0}$ are 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 ${R}_{\mathrm{AA}}$ vs ${p}_{T}$, with a slope of 0.0106${\ifmmode\pm\else\textpm\fi{}}_{0.0029}^{0.0034}$ (Gev/$c$)${}^{\ensuremath{-}1}$, 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 ${\ensuremath{\pi}}^{0}$ yield is measured at different angles with respect to the event plane; a strong azimuthal dependence of the ${\ensuremath{\pi}}^{0}$ ${R}_{\mathrm{AA}}$ 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 perturbative quantum chromodynamics are insufficient to describe the data, while a hybrid model utilizing pQCD for the hard interactions and anti-de-Sitter space/conformal field theory (AdS/CFT) for the soft interactions is consistent with the data.

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