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

Abstract

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