Importance of non-flow background on the chiral magnetic wave search

An observable sensitive to the chiral magnetic wave (CMW) is the charge asymmetry dependence of the ${\pi }^{-}$ and ${\pi }^{+}$ anisotropic flow difference, $\mathrm{\Delta }{v}_n(A_{\mathrm{c}\mathrm{h}})$. We show that, due to non-flow correlations, the flow measurements by the Q-cumulant method using all charged particles as reference introduce a trivial linear term to $\Delta v_{n}(A_{\rm ch})$\mathrm{.}Thetrivialslopecontributiontothetriangleflowdifference$\Delta v_{3}(A_{\rm ch})$ can be negative if the non-flow is dominated by back-to-back pairs. This can explain the observed negative $\mathrm{\Delta }{v}_3(A_{\mathrm{c}\mathrm{h}})$ slope in the preliminary STAR data. We further find that the non-flow correlations give rise to additional backgrounds to the slope of $\mathrm{\Delta }{v}_2(A_{\mathrm{c}\mathrm{h}})$ from the competition among different pion sources and from the larger multiplicity dilution to ${\pi }^{+}$ (${\pi }^{-}$) at positive (negative) $A_{\rm ch}$.