The ring structures that appear in $\mathrm{Au}+\mathrm{Au}$ collisions at collision energies $\sqrt{s_{NN}}=$ 3–30 GeV are studied. The calculations are performed within the model of three-fluid dynamics. It is demonstrated that a pair of vortex rings are formed, one at forward and another at backward rapidities, in ultracentral $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}>$ 4 GeV. The vortex rings carry information about the early stage of the collision, in particular about the stopping of baryons. It is shown that these rings can be detected by measuring the ring observable $R_{\mathrm{\Lambda }}$ even in the rapidity range $0<y<0.5$ (or $-0.5<y<0$) on the level of 0.5–1.5% at $\sqrt{s_{NN}}=$ 5–20 GeV. At forward/backward rapidities, the $R_{\mathrm{\Lambda }}$ signal is expected to be stronger. The possibility of observation of the vortex-ring signal against the background of noncollective transverse polarization is discussed.

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• Hydrodynamic models
• Relativistic heavy-ion collisions