Global polarization of Λ hyperons has been measured to be of the order of a few tenths of a percent in Au+Au collisions at √sNN = 200 GeV, with no significant difference between Λ and Λ. ¯ These new results reveal the collision energy dependence of the global polarization together with the results previously observed at √sNN = 7.7 - 62.4 GeV and indicate noticeable vorticity of the medium created in non-central heavy-ion collisions at the highest RHIC collision energy. The signal is in rough quantitative agreement with the theoretical predictions from a hydrodynamic model and from the AMPT (A Multi-Phase Transport) model. The polarization is larger in more peripheral collisions, and depends weakly on the hyperon's transverse momentum and pseudorapidity ηH within |ηH| < 1. An indication of the polarization dependence on the event-by-event charge asymmetry is observed at the 2σ level, suggesting a possible contribution to the polarization from the axial current induced by the initial magnetic field.
|Original language||English (US)|
|State||Published - May 11 2018|
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