Global polarization of $Λ$, $Ξ^{-}$, and $Ω^{-}$ hyperons in Au+Au collisions at RHIC BES-II energies
Year: 2026
Type: preprint
Abstract: We investigate the global spin polarization of $Λ$ hyperons and the multi-strange hyperons $Ξ^{-}$ and $Ω^{-}$ in Au+Au collisions across the RHIC Beam Energy Scan II (BES-II) energy range, $\sqrt{s_{NN}}=7.7$--$27$ GeV. The polarization is computed using the modified Cooper--Frye formula, which includes contributions from thermal vorticity, the thermal shear tensor, and the gradient of the baryon chemical potential, combined with the (3+1)-dimensional viscous hydrodynamic framework CLVisc with SMASH initial conditions. We present the global polarization as a function of collision energy, centrality, transverse momentum, and rapidity. We find that the global polarization of $Ω^{-}$ is systematically larger than those of $Λ$ and $Ξ^{-}$ because of its larger spin quantum number, but it remains below the central value of the recent STAR measurement. This discrepancy may suggest that additional mechanisms, such as spin correlations among strange quarks inside the $Ω^{-}$, could contribute to the observed $Ω^{-}$ polarization. We also find that the global-polarization splitting between hyperons and anti-hyperons increases toward lower collision energies and is dominated by the chemical-potential-gradient contribution.
Source: arXiv (Cornell University)
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7164211887