Λ( Unknown node mover found in MathML fragment. $ \bar {\Lambda } $ ) polarization in Au+Au collisions at RHIC

Biao Tu,A Yang,A.H Chan,C.H Oh,S.C.C Ng,K.K Phua,W.Y Wang

doi:10.1051/epjconf/201920604003

Biao Tu, A Yang + Show 5 more

Open Access

https://doi.org/10.1051/epjconf/201920604003

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Abstract

Initial large global angular momentum in non-central relativistic heavy-ion collisions can produce strong vorticity, and through the spin-orbit couping, causes the spin of particles to align with the system’s global angular momentum. We present the azimuthal angle dependent (relative to the first-order plane) global polarization for Λ hyperons in midcentral Au+Au collisions at $ \sqrt {S_{NN} } $ = 200 GeV. We also present the polarization of Λ hyperons along the beam direction as a function of Λ hyperons’ emission angle relative to the second-order event plane at $ \sqrt {S_{NN} } $ = 200 GeV. This longitudinal polarization is found to increase in more peripheral collision. The implications of the results are discussed.

Highlights

It is believed that a strongly interacting, hot and dense medium known as Quark Gluon Plasma (QGP) [1] has been created in high-energy heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC)
The STAR experiment at RHIC has observed for the first time a significant alignment between the angular momentum of the medium produced in non-central collisions and the spin of Λ(Λ) hyperons (J=1/2), revealing that the matter produced in heavy-ion collisions is by far the most vortical system ever observed [6]
Such vorticity is expected to depend on hyperon’s azimuthal angle, so far the theoretical guidances on the azimuthal angle dependence of global polarization are not consistent [7,8,9,10,11], due to various treatments on how spin is transported in the fluid

Summary

Introduction

It is believed that a strongly interacting, hot and dense medium known as Quark Gluon Plasma (QGP) [1] has been created in high-energy heavy-ion collisions at the Relativistic Heavy Ion Collider (RHIC). The STAR experiment at RHIC has observed for the first time a significant alignment between the angular momentum of the medium produced in non-central collisions and the spin of Λ(Λ) hyperons (J=1/2), revealing that the matter produced in heavy-ion collisions is by far the most vortical system ever observed [6] Such vorticity is expected to depend on hyperon’s azimuthal angle, so far the theoretical guidances on the azimuthal angle dependence of global polarization are not consistent [7,8,9,10,11], due to various treatments on how spin is transported in the fluid. The study of longitudinal polarization can help us to understand when and how the vorticity and polarization are coupled with other dynamics of the system evolution

Observable

Results

Summary