  The system created in ultrarelativistic nuclear collisions is known to behave
as an almost ideal liquid. In non-central collisions, due to the large orbital
momentum, such a system might be the fluid with the highest vorticity ever
created under laboratory conditions. Particles emerging from such a highly
vorticous fluid are expected to be globally polarized with their spins on
average pointing along the system angular momentum. Vorticity-induced
polarization is the same for particles and antiparticles, but the intense
magnetic field generated in these collisions may lead to the splitting in
polarization. In this paper we outline the thermal approach to the calculation
of the global polarization phenomenon for particles with spin and we discuss
the details of the experimental study of this phenomenon, estimating the effect
of feed-down. A general formula is derived for the polarization transfer in
two-body decays and, particularly, for strong and electromagnetic decays. We
find that accounting for such effects is crucial when extracting vorticity and
magnetic field from the experimental data.
