Measurements of global and local spin polarization of hyperons in Au+Au collisions at RHIC-STAR

¹ Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China
² School of Nuclear Science and Technology, University of Chinese Academy of Sciences, Beijing 100049, China

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Published online: 17 April 2026

Abstract

Vortical structure created in heavy ion collision leads to the polarization of hyperons phenomenon, which can be used as a probe to study the spin degree of freedom. RHIC Beam Energy Scan II program offers a good opportunity to study the hyperon polarization over the wide energy regime. In these proceedings, we report measurements of the global polarization of Λ, Λ̅, Ξ^± and Ω^± at √sNN = 7.7−27 GeV in Au+Au collisions from BES-II. The global hyperons polarization of all hyperons decrease as collision energy increases. Additionally, we report the second harmonics of local Λ, Λ̅ polarization and their difference at √sNN = 7.7−27 GeV, which can be used to probe the baryonic spin Hall effect. These measurements provide valuable insights into the spin dynamics within the QCD medium produced in heavy ion collisions.