Fluid dynamics study of the

With a Yang–Mills field, stratified shear flow initial state and a high resolution ($$3+1$$)D particle-in-cell relativistic (PICR) hydrodynamic model, we calculate the $$\varLambda$$ polarization for peripheral Au + Au collisions at RHIC energy of $$\sqrt{S_{NN}}=200$$ GeV. The obtained longitudinal polarization in our model agrees with the experimental signature and the quadrupole structure on transverse momentum plane. It is found that the relativistic correction (2nd term), arising from expansion and from the time component of the thermal vorticity, plays a crucial role in our results. This term is changing sign and exceeds the first term, arising from the classical vorticity. Finally, the global polarization in our model shows no significant dependence on rapidity, which agrees with the experimental data. It is also found that the second term flattens the sharp peak arising from the classical vorticity (1st term)

A study of

With the PICR hydrodynamic model, we study the polarization splitting between $$\varLambda$$ and $$\bar{\varLambda }$$ at RHIC BES energy range, based on the meson field mechanism. Our results fit to the experimental data fairly well. Besides, two unexpected effect emerges: (1) the baryon density gradient has non-trivial and negative contribution to the polarization splitting; (2) for 7.7 GeV Au+Au collisions within the centrality range of 20–50%, the polarization splitting surprisingly increases with the centrality decreases. The second effect might help to explain the significant signal of polarization splitting measured in STAR’s Au+Au 7.7 Gev collisions