Limitation of multiparticle correlations for studying the event-by-event distribution of harmonic flow in heavy-ion collisions

The sensitivity of flow harmonics from cumulants to the event-by-event flow distribution p(vn) is investigated using a simple central moment expansion approach. For a narrow distribution whose width is much smaller than the mean σn(vn), the differences between the first three higher-order cumulant estimates vn{4},vn{6}, and vn{8} are not very sensitive to the shape of p(vn). For a broad distribution σn/vn, the higher-order cumulant estimates differ from each other but may change sign and become ill defined. This sign change arises from the choice of p(vn), without the need to invoke nonflow effects. Direct extraction of p(vn) via a data-driven unfolding method used by the ATLAS experiment is a more preferred approach for flow distribution measurement.