Isolation of Flow and Nonflow by Two- and Multi-Particle Cumulant Measurements of $v_n$ in $\sqrt{s_{NN}} = 200$ GeV Au+Au Collisions by STAR

TL;DR

This paper introduces a data-driven approach to separate flow and nonflow effects in heavy-ion collision data using multi-particle cumulant measurements, revealing flow's eta-independence and nonflow's eta-dependence.

Contribution

It presents a novel method to distinguish flow from nonflow correlations in heavy-ion collisions using two- and multi-particle cumulants, enhancing understanding of flow fluctuations.

Findings

Flow is eta-independent within the STAR TPC

Nonflow is eta-dependent and causes the eta drop in two-particle v2

Combining cumulants provides insights into flow fluctuations

Abstract

We apply a data-driven method to STAR Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV to isolate $\Delta\eta$-dependent and $\Delta\eta$-independent correlations by using two- and four-particle Q-cumulant $v_{n}$ measurements. The $\Delta\eta$-independent part, dominated by flow, is found to be $\eta$-independent within the STAR TPC of $\pm1$ unit of pseudo-rapidity. The $\Delta\eta$-dependent part may be associated to nonflow, and is responsible for the $\Delta\eta$ drop in the measured two-particle $v_{2}$ cumulant. We combine our result to four- and six-particle cumulants to gain further insights on the nature of flow fluctuations.