Estimate of the signal from the chiral magnetic effect in heavy-ion collisions from measurements relative to the participant and spectator flow planes

An interpretation of the charge-dependent correlations sensitive to the chiral magnetic effect (CME)—–the separation of the electric charges along the system magnetic field (across the reaction plane)—–is ambiguous due to possible large background (non-CME) effects. The background contribution is proportional to the elliptic flow $v_2$; it is the largest in measurements relative to the participant plane and is smaller in measurements relative to the flow plane determined by spectators, where the CME signal, in contrast, is likely larger. In this paper, I discuss a possible strategy for corresponding experimental measurements and list and evaluate different assumptions related to this approach.