We investigate hydrodynamic effects on the spin polarization of $\Lambda$ hyperons in Au+Au collisions at $\sqrt{ s_{ NN}} = 200$ GeV and p+Pb collisions at $\sqrt{ s_{ NN}} = 8.16$ TeV using the CLVisc hydrodynamic framework. We present numerical results for the second Fourier sine coefficient of the longitudinal spin polarization, $\langle P_{ z} \sin 2(\phi_{ p} - \Psi_{ 2}) \rangle$, as a function of multiplicity (centrality) under three equilibrium scenarios: $\Lambda$ equilibrium, $s$-quark equilibrium, and isothermal equilibrium. We highlight the respective roles of thermal vorticity and the thermal-shear tensor in generating $\langle P_{ z} \sin 2(\phi_{ p} - \Psi_{ 2}) \rangle$ across collision systems and scenarios.
Categories: nucl-th