Abstract
We study the global polarizations of Λ, Ξ−, and Ω− hyperons in noncentral Au + Au collisions at √SNN = 7.7-200 GeV. We highlight the importance of effect of decay feeddown to the measured global polarization. With the decay contributions taken into account, the global polarization ordering PΩ− > PΞ− > PΛ can be naturally explained, which is consistent with the observation recently reported from the STAR experiment from Au+Au collisions at 200 GeV. We also extend our calculations to predict expectations from the RHIC-BES II data.
Highlights
The large orbital angular momentum produced by relativistic heavy-ion collisions leads to the spin polarization of final-state hadrons [1, 2]
Local polarization distribution caused by the quark-gluon plasma (QGP) anisotropic expansion, which does not contribute to the global polarization, can lead to ρ00 1/3 [17]
We expect that the global polarizations of the three hyperons have a similar energy dependence — they all decrease with the increase of collision energy, as demonstrated in hyperons approximately fulfill PΛ : PΞ− : PΩ− 1 : 1 : 5/3
Summary
The large orbital angular momentum produced by relativistic heavy-ion collisions leads to the spin polarization of final-state hadrons [1, 2]. The data in the energy range of sNN = 7.7–5020 GeV [3, 4, 6] demonstrate an increasing global Λ (Λ ) polarization with the decreasing collision energy This trend can be reproduced by many model calculations, such as [8,9,10,11,12], which provides strong support to the vorticity interpretation of the global polarization. Local polarization distribution caused by the QGP anisotropic expansion, which does not contribute to the global polarization, can lead to ρ00 1/3 [17] This makes the spin alignment of vector mesons more complicated than the global polarization of hyperons. The study improves our understanding of the global hyperon polarization and provides predictions for future measurements at RHIC-BES energies
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