Probing early-time longitudinal dynamics with the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi mathvariant="normal">Λ</mml:mi></mml:math> hyperon's spin polarization in relativistic heavy-ion collisions

We systematically study the hyperon global polarization's sensitivity to collision systems' initial longitudinal flow velocity in hydrodynamic simulations. By explicitly imposing local energy-momentum conservation when mapping geometry macroscopic fields, we evolution of orbital angular momentum (OAM) and fluid vorticity. find that a simultaneous description $\Lambda$ hyperons' polarization slope pion's directed can strongly constrain size at beginning evolution. extract fraction produced QGP as function energy with STAR measurements RHIC Beam Energy Scan program. there is about 100-200 $\hbar$ OAM remains mid-rapidity further exam effects different gradients on spin $\bar{\Lambda}$. The $\mu_B/T$ change ordering between $\Lambda$'s $\bar{\Lambda}$'s polarization.