Isolation of Flow and Nonflow Correlations by Two- and Four-Particle Cumulant Measurements of Azimuthal Harmonics in $\sqrt{s_{{}_{\mathrm{N}\mathrm{N}}}}=$ 200 GeV Au+Au Collisions

A data-driven method was applied to measurements of Au+Au collisions at $\sqrt{s_{{}_{\mathrm{N}\mathrm{N}}}}=$ 200 GeV made with the STAR detector at RHIC to isolate pseudorapidity distance $\mathrm{\Delta }\eta$-dependent and $\mathrm{\Delta }\eta$-independent correlations by using two- and four-particle azimuthal cumulant measurements. We identified a component of the correlation that is $\mathrm{\Delta }\eta$-independent, which is likely dominated by anisotropic flow and flow fluctuations. It was also found to be independent of $\eta$ within the measured range of pseudorapidity $\mathrm{\mid }\eta \mathrm{\mid }<1$. The relative flow fluctuation was found to be $34% \pm 2% (stat.) \pm 3% (sys.)$forparticlesoftransversemomentum$p_{T}$lessthan$2$GeV\mathrm{/}$c$\mathrm{.}The$\Delta\eta$-dependent part may be attributed to nonflow correlations, and is found to be $5\mathrm{\%}\pm 2\mathrm{\%}(sys\mathrm{.})$ relative to the flow of the measured second harmonic cumulant at $\mathrm{\mid }\mathrm{\Delta }\eta \mathrm{\mid }>0.7$.