Implications of directed flow and UPC measurements for electromagnetic and vorticity fields in heavy ion collisions

The electro-magnetic (EM) field generated by a moving heavy nucleus enables us to study many interesting emergent phenomena associated with EM field effects in heavy ion collisions. The time evolution of the EM field is still a hot topic for debate. Theoretical calculations indicate that charge dependent direct flow is sensitive to EM field effects. Experimentally multi-differential measurements of charge dependent direct flow have been made. In addition, dileptons from the photon-photon process in ultraperipheral heavy ion collisions (UPC) are sensitive to initial EM field. Similar measurements in peripheral to semi-central collisions have a potential to pin down possible final-state EM field.

 

I will review recent results of direct flow and UPC measurements and discuss the implications for EM and vorticity fields in heavy ion collisions.  Future perspectives will be discussed as well.