Complications in the interpretation of the charge asymmetry dependent $\pi$ flow for the chiral magnetic wave

Understand

The charge asymmetry ($A_{\rm ch}$) dependence of the $\pi^{-}$ and $\pi^{+}$ elliptic flow difference, $\Delta v_{2}(A_{\rm ch})$, has been regarded as a sensitive observable for the possible chiral magnetic wave (CMW) in relativistic heavy ion collisions.

• In this work, we first demonstrate that, due to non-flow backgrounds, the flow measurements by the Q-cumulant method using all charged particles as reference introduce a trivial linear term to $\Delta v_{2}(A_{\rm ch})$.
• The trivial slope can be negative in the triangle flow difference $\Delta v_{3}(A_{\rm ch})$ if the non-flow is dominated by back-to-back pairs.
• After eliminating the trivial term, we find that the non-flow between like-sign pairs gives rise to an additional positive slope to $\Delta v_{2}(A_{\rm ch})$ because of the larger dilution effect to $\pi^{+}$ ($\pi^{-}$) at positive (negative) $A_{\rm ch}$.