Suppression Pattern of Neutral Pions at High Transverse Momentum in $\mathrm{Au}+\mathrm{Au}$ Collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$ and Constraints on Medium Transport Coefficients

For $\mathrm{Au}+\mathrm{Au}$ collisions at 200 GeV, we measure neutral pion production with good statistics for transverse momentum, $p_T$, up to $20\mathrm{GeV}/c$. A fivefold suppression is found, which is essentially constant for $5<p_T<20\mathrm{GeV}/c$. Experimental uncertainties are small enough to constrain any model-dependent parametrization for the transport coefficient of the medium, e.g., $⟨\widehat{q}⟩$ in the parton quenching model. The spectral shape is similar for all collision classes, and the suppression does not saturate in $\mathrm{Au}+\mathrm{Au}$ collisions.

Figure 1

Top: ${\pi }^0$ invariant yields for all centralities and minimum bias. Bottom: ratios of the (separately analyzed) PbSc and PbGl yields to the combined minimum bias invariant yield, which is shown in the top panel.

Figure 2

Nuclear modification factor ($R_{\mathrm{AA}}$) for ${\pi }^0\mathrm{s}$. Error bars are statistical and $p_T$-uncorrelated errors, boxes around the points indicate $p_T$-correlated errors. Single box around $R_{\mathrm{AA}}=1$ on the left is the error due to $N_{\mathrm{coll}}$, whereas the single box on the right is the overall normalization error of the $p+p$ reference spectrum.

Figure 3

Left: ${\pi }^0$ $R_{\mathrm{AA}}$ for the most central (0–5%) $\mathrm{Au}+\mathrm{Au}$ collisions and PQM model calculations for different values of $⟨\widehat{q}⟩$. Right: ${\tilde{\chi }}^2({ϵ}_b,{ϵ}_c,p)$ distribution for the corresponding values of $⟨\widehat{q}⟩$. The bold (red) curve in the left panel and the round (red) point in the right panel are the best fit values.

Figure 4

Integrated nuclear modification factor ($R_{\mathrm{AA}}$) for ${\pi }^0$ as a function of collision centrality expressed in terms of $N_{\mathrm{part}}$. The error bars/bands are the same as in Fig. 2. The two lines at unity show the errors on $⟨N_{\mathrm{coll}}⟩$. The last two points correspond to partially overlapping centrality bins. The dashed lines show the fit explained in the text.