Spectator charge splitting of directed flow in heavy ion collisions

Abstract: We estimate the effect of the spectator charge on distortion of single charged pion distributions as well as on azimuthal anisotropies in heavy ion collisions. A large electromagnetic effect on directed flow $v_1$ is predicted in good agreement with existing WA98 as well as RHIC data. This effect results in a splitting of $v_1$ for positive and negative pions. Detailed analysis of this phenomenon may provide new information on the collision dynamics.