  Particle spin polarization is known to be linked both to rotation (angular
momentum) and magnetization of a many particle system. However, in the most
common formulation of relativistic kinetic theory, the spin degrees of freedom
appear only as degeneracy factors multiplying phase-space distributions. Thus,
it is important to develop theoretical tools that allow to make predictions
regarding the spin polarization of particles, which can be directly confronted
with experimental data. Herein, we discuss a link between the relativistic spin
tensor and particle spin polarization, and elucidate the connections between
the Wigner function and average polarization. Our results may be useful for
theoretical interpretation of heavy-ion data on spin polarization of the
produced hadrons.
