Nonflow “factorization” and a novel method to disentangle anisotropic flow and nonflow

Anisotropic flow, which arises from correlations to common collision geometry, is sensitive to hydrodynamic expansion of the medium created in heavy-ion collisions and has been extensively studied. Anisotropic flow is quantified by the Fourier series in particle azimuthal angle relative to the reaction plane. It is measured using azimuthal correlations of final-state particles and therefore is contaminated by correlations unrelated to the reaction plane (nonflow). Currently anisotropic flow and nonflow cannot be experimentally separated in a model-independent manner. Using pythia simulations of $p+p$ collisions we show that nonflow approximately factorizes in transverse momentum. This fact may be used to disentangle flow and nonflow in heavy-ion data by performing a two-component factorization fit to Fourier coefficients of two-particle cumulants.