Experimental progress on particle polarization in heavy-ion collisions

In non-central heavy-ion collisions, an initial orbital angular momentum carried by two colliding nuclei is partially transferred to the created medium, resulting in particle polarization on average along the direction of the system angular momentum via spin-orbit coupling, referred to as global polarization. The observations of the global polarization of hyperons as well as local polarization induced by anisotropic collective flow have opened new directions in the study of nuclear collision dynamics and properties of quark-gluon plasma (QGP), and for understanding the spin dynamics in the QGP. There have been a lot of progress in both experimental and theoretical studies. In this talk, we review results on polarization measurements in heavy-ion collisions and discuss what we have learned so far with open questions and future perspectives.