  Recently studies of the differential nature of the flow angle fluctuations,
known as event plane angular decorrelation, indicated that measurements that
assume a common symmetry plane may need to consider the flow angle fluctuations
effect. Using the HIJING and AMPT models, it is shown that the flow angle
fluctuations measurements, obtained with the two- and three-subevents
correlation method, could have significant non-flow effects associated with
long- and short-range non-flow correlations. The current study demonstrates the
four-subevents cumulant methods' ability to reduce the non-flow effects. It is
further argued that the measurements using the four-subevents correlation
method can be used to provide accurate quantification of the differential flow
angle fluctuations.
