Spin dynamics in intermediate-energy heavy-ion collisions with rigorous angular momentum conservation

We have revisited the spin dynamics in intermediate -energy heavy -ion collisions based on the improved spinand isospin-dependent Boltzmann-Uehling-Uhlenbeck (SIBUU) transport model, particularly with the constraint of rigorous angular momentum conservation incorporated. We have studied the spin polarization of free nucleons and tritons/ 3He as well as the spin alignment of deuterons, and predicted the flow splittings for their different spin states. We have also demonstrated that the spin -dependent potential may enhance dissipations and thus have a non -negligible effect on the spin -averaged transverse flow at low collision energies. When rigorous angular momentum conservation in each spin -dependent nucleon -nucleon collision is incorporated, it affects the overall dynamics, the flow, and also the spin polarization, while the effects of the spin -orbit potential on the spinrelated observables are still appreciable. The well -developed SIBUU model could be further extended to include hyperons or vector mesons, or used as a hadronic afterburner for spin -related studies in relativistic heavy -ion collisions, with more inelastic channels incorporated in the future.