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arXiv · 1803.00867

Probing vorticity structure in heavy-ion collisions by local $Λ$ polarization

Xiao-Liang Xia·Hui Li·Zebo Tang·Qun Wang
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Abstract

We study the local structure of the vorticity field and the $Λ$ polarization in Au+Au collisions in the energy range $\sqrt{s_{\mathrm{NN}}}=7.7$--$200$ GeV and Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2760$ GeV using A Multi-Phase Transport (AMPT) model. We focus on the vorticity field arising from the non-uniform expansion of the fireball, which gives the circular structure of the transverse vorticity $\boldsymbolω_{\perp}=(ω_{x},ω_{y})$ around the $z$ direction as well as the quadrupole pattern of the longitudinal vorticity $ω_{z}$ in the transverse plane. As a consequence, the three components of the polarization vector $\mathbf{P}=(P_{x},P_{y},P_{z})$ for $Λ$ hyperons show harmonic behaviors as $\mathrm{sgn}(Y)\sinϕ_{p}$, $-\mathrm{sgn}(Y)\cosϕ_{p}$, and $-\sin(2ϕ_{p})$, where $ϕ_{p}$ and $Y$ are the azimuthal angle and rapidity in momentum space. These patterns of the local $Λ$ polarization are expected to be tested in future experiments.

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Xiao-Liang Xia, Hui Li, Zebo Tang, Qun Wang. 2018-08-01. Probing vorticity structure in heavy-ion collisions by local $Λ$ polarization. https://doi.org/10.1103/physrevc.98.024905

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