“…where the brakets • • • indicate the average over the particles in the collision, is related to a collective sidewards deflection of particles on the event plane with respect to the beam axis (v 1 ∼ p x / p T ) and the geometry of EMF and fluid velocities requires that the Lorentz force produces a net push of charges along the x axis with opposite directions for positively and negatively charges. Hence, the splitting of the directed flow between particles with the same mass and different electric charge gives direct access to the collective electromagnetic response of the medium [11,13,19,20,[22][23][24][25][26][27]. Furthermore, the measurements of the v 1 produced in different colliding systems as well as for different energies and centralities [28][29][30][31][32][33] give the opportunity to theoretical models to test their description of the initial state of highenergy collision, especially in view of the combined influence of EMF and vortical dynamics on the directed flow with a different sensitivity for bulk light particles and early-produced heavy quarks [11,13,19,20,[22][23][24][25][26][27][34][35][36].…”