Particle-type dependence of azimuthal anisotropy and nuclear modification of particle production in Au+Au collisions at s(NN)**(1/2) = 200-GeV

Abstract

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

Figures (4)

• Figure 1: (color online). 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 non-flow systematic uncertainties are approximately -20%. Hydrodynamical calculations of $v_2$ for pions, kaons, protons and lambdas are also plotted hydroPasi01.
• Figure 2: (color online). 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 non-flow systematic errors for the 30--70%, 5--30% and 0--5% centralities are -25%, -20% and -80% respectively.
• Figure 3: (color online). The ratio $R_{CP}$ for $K_{S}^{0}$, $K^{\pm}$, and $\Lambda +\overline{\Lambda}$ at mid-rapidity calculated using centrality intervals, 0--5% vs. 40--60% (top) and 0--5% vs. 60--80% of the collision cross section (bottom). 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 $\mathrm{N_{bin}}$ and $\mathrm{N_{part}}$. We also show the charged hadron $R_{CP}$ measured by STAR for $\sqrt{s_{_{NN}}}=200$ GeV highpt200.
• Figure 4: (color online). 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 non-flow systematic uncertainties are approximately -20%.