The Chiral Magnetic Wave (CMW) [1] predicts a dependence of the positive and negative particle elliptic flow on the event charge asymmetry. Such a dependence has been observed by the STAR Collaboration [2]. However, it is rather difficult to interpret the results of this measurement, as well as to perform cross-experiment comparisons, due to the dependence of the observable on experimental inefficiencies and the kinematic acceptance used to determine the net asymmetry. We propose another observable that is free from these deficiencies. It also provides possibilities for differential measurements clarifying the interpretation of the results. We use this new observable to study the effect of the local charge conservation that can mimic the effect of the CMW in charge dependent flow measurements.
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