Global Polarization of $\Xi$ and $\Omega$ Hyperons in Au+Au Collisions at $\sqrt {s_{NN}}$ = 200  GeV

Global polarization of Ξ and Ω hyperons has been measured for the first time in Au+Au collisions at sNN=200 GeV. The measurements of the Ξ- and Ξ¯+ hyperon polarization have been performed by two independent methods, via analysis of the angular distribution of the daughter particles in the parity violating weak decay Ξ→Λ+π, as well as by measuring the polarization of the daughter Λ hyperon, polarized via polarization transfer from its parent. The polarization, obtained by combining the results from the two methods and averaged over Ξ- and Ξ¯+, is measured to be ⟨PΞ⟩=0.47±0.10(stat)±0.23(syst)% for the collision centrality 20%–80%. The ⟨PΞ⟩ is found to be slightly larger than the inclusive Λ polarization and in reasonable agreement with a multiphase transport model. The ⟨PΞ⟩ is found to follow the centrality dependence of the vorticity predicted in the model, increasing toward more peripheral collisions. The global polarization of Ω, ⟨PΩ⟩=1.11±0.87(stat)±1.97(syst)% was obtained by measuring the polarization of daughter Λ in the decay Ω→Λ+K, assuming the polarization transfer factor CΩΛ=1.

Note:

7 pages, 3 figures, Accepted for publication in Physical Review Letters

Nuclear Physics
hyperon: polarization
heavy ion: scattering
decay: weak interaction
parity: violation
angular distribution
transport theory
peripheral
numerical calculations
experimental results

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Global Polarization of Ξ\XiΞ and Ω\OmegaΩ Hyperons in Au+Au Collisions at sNN\sqrt {s_{NN}}sNN​​ = 200 GeV

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Global Polarization of $\Xi$ and $\Omega$ Hyperons in Au+Au Collisions at $\sqrt {s_{NN}}$ = 200 GeV