Measurements of Higher Order Flow Harmonics in $\mathrm{Au}+\mathrm{Au}$ Collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$

Flow coefficients $v_n$ for $n=2$, 3, 4, characterizing the anisotropic collective flow in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$, are measured relative to event planes ${\Psi }_n$, determined at large rapidity. We report $v_n$ as a function of transverse momentum and collision centrality, and study the correlations among the event planes of different order $n$. The $v_n$ are well described by hydrodynamic models which employ a Glauber Monte Carlo initial state geometry with fluctuations, providing additional constraining power on the interplay between initial conditions and the effects of viscosity as the system evolves. This new constraint can serve to improve the precision of the extracted shear viscosity to entropy density ratio $\eta /s$.

Figure 1

Raw correlation strengths $⟨\cos (j[{\Phi }_n^A-{\Phi }_m^B])⟩$ and $⟨\cos (j[{\Phi }_n^C-{\Phi }_m^D])⟩$ of the event planes for various detector combinations as a function of the collision centrality, binned in percentages of the total cross section, where 0% corresponds to impact $\mathrm{\text{parameter}}=0$. Panels (a) and (b) show the two subevent correlations for $m=n$; (c) and (d) show the two subevent correlations for $m\ne n$. The detectors in which the event plane is measured are: $A$: RXN North, $B$: BBC South, $C$: MPC North, and $D$: MPC South. Data in (b) and (d) have been scaled by factors of 10 and 20, respectively.

Figure 2

$v_n\{{\Psi }_n\}$ vs $p_T$ measured via the reaction-plane method for different centrality bins; 0%–10% are the most central collisions. Shaded (gray and pink) and hatched (blue) areas around the data points indicate sizes of systematic uncertainties. The curves in panels (b) and (d) are predictions for $v_2\{{\Psi }_2\}$ and $v_3\{{\Psi }_3\}$ from two hydrodynamic models, both using Glauber initial conditions and $4\pi \eta /s=1$, Alver et al. [27] and Schenke et al. [32].

Figure 3

Comparison of [(a) and (b)] $v_2\{{\Psi }_2\}$ vs $N_{\mathrm{part}}$ and [(c) and (d)] $v_3\{{\Psi }_3\}$ vs $N_{\mathrm{part}}$ measurements and theoretical predictions (see text): “MC-KLN $+$ $4\pi \eta /s=2$” and “Glauber $+$ $4\pi \eta /s=1$ (1)” [27]; “Glauber $+$ $4\pi \eta /s=1$ (2)” [32]; and “UrQMD” [29]. Shaded areas (magenta) around the data points indicate sizes of systematic uncertainties.