Global $\Lambda$ polarization in heavy-ion collisions at energies 2.4--7.7 GeV: Effect of Meson-Field Interaction

Abstract

Based on the three-fluid model, the global $\Lambda$ polarization in Au+Au collisions at 2.4 $\le \sqrt{s_{NN}}\le$ 7.7 GeV is calculated, including its rapidity and centrality dependence. Contributions from the thermal vorticity and meson-field term (proposed by Csernai, Kapusta and Welle) to the global polarization are considered. The results are compared with data from recent and ongoing STAR and HADES experiments. It is predicted that the polarization maximum is reached at $\sqrt{s_{NN}}\approx$ 3 GeV, if the measurements are performed with the same acceptance. The value of the polarization is very sensitive to interplay of the aforementioned contributions. In particular, the thermal vorticity results in quite strong increase of the polarization from the midrapidity to forward/backward rapidities, while the meson-field contribution considerably flattens the rapidity dependence. The polarization turns out to be very sensitive to details of the equation of state. While collision dynamics become less equilibrium with decreasing collision energy, the present approach to polarization is based on the assumption of thermal equilibrium. It is found that equilibrium is achieved at the freeze-out stage, but this equilibration takes longer at moderately relativistic energies.

12 pages, 14 figures, minor corrections, version published in PRC

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• $\Lambda$ and $\overline{\Lambda }$ Freeze-Out Distributions and Global Polarizations in Au+Au Collisions
• Impact of strong magnetic field, baryon chemical potential, and medium anisotropy on polarization and spin alignment of hadrons
• Hyperon global polarization in heavy-ion collisions at NICA energies. Feed-down effects and the role of ${\Sigma }^0$ hyperons
• Hyperon Production in Bi+Bi Collisions at NICA and Angular Dependence of Hyperon Spin Polarization
• Vortex rings in heavy-ion collisions at energies $\sqrt{s_{NN}}=$ 3--30 GeV and possibility of their observation
• Polarization in heavy ion collisions: a theoretical review
• Global $\Lambda$ polarization in heavy-ion collisions at high baryon density