We have computed 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 or centrality in Au+Au collisions at $\sqrt{ s_{ NN}} = 200$ GeV and in $p$+Pb collisions at $\sqrt{ s_{ NN}} = 8.16$ TeV using the CLVisc hydrodynamic framework. The numerical results successfully describe the data in Au+Au collisions. However, understanding the data in $p$+Pb collisions remains a puzzle. Additionally, we have reported some recent developments in quantum kinetic theory and spin hydrodynamics.
Categories: nucl-th hep-ph