Particle-Type Dependence of Azimuthal Anisotropy and Nuclear Modification of Particle Production in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ Collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$

We present STAR measurements of the azimuthal anisotropy parameter $v_2$ and the binary-collision scaled centrality ratio $R_{\mathrm{C}\mathrm{P}}$ for kaons and lambdas ($\Lambda +\overline{\Lambda }$) at midrapidity in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$. In combination, the $v_2$ and $R_{\mathrm{C}\mathrm{P}}$ particle-type dependencies contradict expectations from partonic energy loss followed by standard fragmentation in vacuum. We establish $p_T\approx 5\mathrm{G}\mathrm{e}\mathrm{V}/c$ as the value where the centrality dependent baryon enhancement ends. The $K_S^0$ and $\Lambda +\overline{\Lambda }$ $v_2$ values are consistent with expectations of constituent-quark-number scaling from models of hadron formation by parton coalescence or recombination.

Figure 1

The minimum bias (0%–80% of the collision cross section) $v_2(p_T)$ for $K_S^0$, $\Lambda +\overline{\Lambda }$, and $h^{\pm }$. The error bars shown include statistical and point-to-point systematic uncertainties from the background. The additional nonflow systematic uncertainties are approximately $-20\%$. Hydrodynamical calculations of $v_2$ for pions, kaons, protons, and lambdas are also plotted [10].

Figure 2

The $v_2$ of $K_S^0$ and $\Lambda +\overline{\Lambda }$ as a function of $p_T$ for 30%–70%, 5%–30%, and 0%–5% of the collision cross section. The error bars represent statistical errors only. The nonflow systematic errors for the 30%–70%, 5%–30%, and 0%–5% centralities are $-25\%$, $-20\%$, and $-80\%$, respectively.

Figure 3

The ratio $R_{\mathrm{C}\mathrm{P}}$ for $K_S^0$, $K^{\pm }$, and $\Lambda +\overline{\Lambda }$ at midrapidity calculated using centrality intervals, 0%–5% vs 40%–60% (top panel) and 0%–5% vs 60%–80% of the collision cross section (bottom panel). The error bars shown on the points include both statistical and systematic errors. The widths of the gray bands represent the uncertainties in the model calculations of $N_{\mathrm{b}\mathrm{i}\mathrm{n}}$ and $N_{\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{t}}$. We also show the charged hadron $R_{\mathrm{C}\mathrm{P}}$ measured by STAR for $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}/c$ [15].

Figure 4

The $v_2$ parameter for $K_S^0$ and $\Lambda +\overline{\Lambda }$ scaled by the number of constituent quarks ($n$) and plotted versus $p_T/n$. The error bars shown include statistical and point-to-point systematic uncertainties from the background. The additional nonflow systematic uncertainties are approximately $-20\%$.