Vortex rings in event-by-event relativistic heavy-ion collisions

Vortices such as smoke rings in air are familiar features in hydrodynamics. They appear when fast-moving local currents are embedded in the larger medium. This paper reports on results of realistic simulations of relativistic heavy-ion collisions using relativistic fluid dynamics. The work highlights the formation of a novel toroidal vortex ring structure which could manifest itself in the polarization of the $\mathrm{\ensuremath{\Lambda}}$ hyperon. This proposed new observable is argued to have great potential as a probe of hydrodynamic behavior in small collision systems, and of early-time dynamics in general. The predictions made in this work can be tested by experiments performed at current heavy-ion colliders such as RHIC at BNL and the LHC at CERN, as well as by future fixed-target experiments to be carried out at the LHC.