Measurement of the higher-order anisotropic flow coefficients for identified hadrons in Au$+$Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV

TL;DR

This paper reports new measurements of higher-order anisotropic flow coefficients for identified hadrons in Au+Au collisions at 200 GeV, revealing hydrodynamic behavior and quark number scaling, with implications for understanding the quark-gluon plasma.

Contribution

It provides the first detailed measurement of higher-order flow coefficients for identified particles at RHIC energies, demonstrating quark number scaling and constraining freeze-out eccentricities.

Findings

Flow coefficients exhibit hydrodynamic patterns.

Quark number scaling holds across particle species.

Freeze-out eccentricities are smaller than initial geometric values.

Abstract

New PHENIX measurements of the anisotropic flow coefficients $v_2\{\Psi_2\}$, $v_3\{\Psi_3\}$, $v_4\{\Psi_4\}$ and $v_4\{\Psi_2\}$ for identified particles ($\pi^{\pm}$, $K^{\pm}$, and $p+\bar{p}$) obtained relative to the event planes $\Psi_n$ in Au$+$Au collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV are presented as functions of collision centrality and particle transverse momenta $p_T$. The $v_n$ coefficients show characteristic patterns consistent with hydrodynamical expansion of the matter produced in the collisions. For each harmonic $n$, a modified valence quark number $n_q$ scaling plotting $v_n/(n_q)^{n/2}$ versus ${\rm KE}_T/n_q$ is observed to yield a single curve for all the measured particle species for a broad range of transverse kinetic energies ${\rm KE}_T$. A simultaneous blast wave model fit to the observed particle spectra and $v_n(p_T)$ coefficients identifies spatial eccentricities $s_n$ at freeze-out, which are much smaller than the initial-state geometric values.