Abstract
We compute the fermion spin distribution in the vortical fluid created in off-central high energy heavy-ion collisions. We employ the event-by-event (3+1)D viscous hydrodynamic model. The spin polarization density is proportional to the local fluid vorticity in quantum kinetic theory. As a result of strong collectivity, the spatial distribution of the local vorticity on the freeze-out hyper-surface strongly correlates to the rapidity and azimuthal angle distribution of fermion spins. We investigate the sensitivity of the local polarization to the initial fluid velocity in the hydrodynamic model and compute the global polarization of Λ hyperons by the AMPT model. The energy dependence of the global polarization agrees with the STAR data.
Highlights
The STAR collaboration has measured the polarization of Λ and Λhyperons [1]
The A Multi-Phase Transport (AMPT) model is employed to generate the initial energy density with the global angular momentum given by the asymmetry between forward and backward going participants separated by the impact parameter in the transverse plane
We compute the local polarization of Λ by the CLVisc model with the initial transverse flow vx and vy given by the energy-momentum tensor T μν of initial partons by the AMPT
Summary
The STAR collaboration has measured the polarization of Λ and Λhyperons [1]. H. Li et al / Nuclear Physics A 967 (2017) 772–775 (3+1)D viscous hydrodynamic model and the beam energy dependence of the global Λ polarization within A Multi-Phase Transport (AMPT) [12] model. The local polarization density on the freeze-out hyper-surface reads [11, 14], Pμ dΠμ(p)/d3 p dN/d3 p
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