System size and beam energy dependence of azimuthal anisotropy from PHENIX

TL;DR

This paper reports measurements of azimuthal anisotropy in gold-gold and copper-copper collisions at different energies, analyzing how flow coefficients depend on system size, energy, and particle transverse momentum, revealing scaling behaviors and non-flow effects.

Contribution

It provides new insights into the system size and energy dependence of flow harmonics and examines the validity of quark number scaling in different collision systems and energies.

Findings

NCQ scaling holds for certain energies and systems.

Non-flow effects influence high-$p_T$ $v_2$ measurements.

$v_4$ scales with $v_2$ in central collisions.

Abstract

We present azimuthal anisotropy measurements in Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV. Comparison between reaction plane and cumulant $v_2$ measurements in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV show that non-flow contributions, originating mainly from jets, influence the extracted $v_2$ for $p_T$ $\gtrsim$ 3.5 GeV/c. Number of constituent quark (NCQ) scaling of $v_2$, when studied as a function of transverse kinetic energy $KE_T$, is seen to hold for Au+Au collisions at $\sqrt{s_{NN}}$ = 62.4 and 200 GeV and for Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV for $KE_{T}$ $\lesssim$ 1 GeV/c. Differential hexadecupole flow $v_4$ seems to exhibit scaling with integral $v_2$ for centrality $\le$ 40% as has been observed for differential $v_2$.