Suppression pattern of neutral pions at high transverse momentum in Au+Au collisions at sqrt(s_NN) = 200 GeV and constraints on medium transport coefficients

TL;DR

For Au + Au collisions at 200 GeV, neutral pion production is measured with good statistics for transverse momentum, pT, and a fivefold suppression is found, which is essentially constant for 5 < pT < 20 GeV/c.

Abstract

For Au + Au collisions at 200 GeV we measure neutral pion production with good statistics for transverse momentum, p_T, up to 20 GeV/c. A fivefold suppression is found, which is essentially constant for 5 < p_T < 20 GeV/c. Experimental uncertainties are small enough to constrain any model-dependent parameterization for the transport coefficient of the medium, e.g. \mean(q^hat) in the parton quenching model. The spectral shape is similar for all collision classes, and the suppression does not saturate in Au+Au collisions; instead, it increases proportional to the number of participating nucleons, as N_part^2/3.

Figures (4)

• Figure 1: Left: $\pi^0$ invariant yields for different centralities (PbSc and PbGl combined). Right: consistency between the results obtained separately from PbSc and PbGl
• Figure 2: Nuclear modification factor ($R_{\rm AA}$) for $\pi^0$s. Error bars are statistical and $p_{\rm T}$-uncorrelated errors, boxes around the points indicate $p_{\rm T}$-correlated errors. Single box around $R_{\rm AA}$=1 on the left is the error due to $N_{\rm coll}$, whereas the single box on the right is the overall normalization error of the p+p reference spectrum.
• Figure 3: Left: $\pi^0$$R_{\rm AA}$ for the most central (0-5%) Au+Au collisions and PQM model calculations for different values of $\left\langle \hat{q} \right\rangle$. Red curve: best fit. Right: $\tilde{\chi}^2(\epsilon_{b}, \epsilon_{c}, {p})$ distribution for a wide range of values of $\left\langle \hat{q} \right\rangle$.
• Figure 4: Integrated nuclear modification factor ($R_{\rm AA}$) for $\pi^0$ as a function of collision centrality expressed in terms of $N_{\rm part}$. The error bars/bands are the same as in Fig. \ref{['fig:RAA']}. The last two points correspond to overlapping centrality bins, 0-10% and 0-5%. The dashed lines show the fit to a function. See text.