Investigate the and ()over-bar polarization splitting effect with combined mechanisms

The significant splitting of Lambda and (Lambda) over bar polarization measured in STAR's Au + Au 7.7GeV collisions seems to be huge and unable to be described satisfactorily by any single mechanism, thus we revisit and combine there different mechanisms together on the basis of our PICR hydrodynamic model, to explain the experimental data. The three mechanisms, i.e. the meson field mechanism, the freeze-out space-time mechanism, and the QGP's magnetic field mechanism, lie on different stages of high energy collisions, and thus are not contradicted with each other. We find that the meson field mechanism is dominat, while the QGP's magnetic field mechanism is rather trivial, and freeze-out time effect is restricted by the small FZ time difference, leading to a hierarchy of Delta P-J >> Delta P-t >> Delta P-m. Besides, the com-bination of different mechanisms could promote the mean value of polarization splitting from about 3%-4% to 4.5%, which is closer to the experimental measured mean value of 5.8%.