Abstract
We expect that the same phenomena also exist in heavy ion collisions. Huge global angular momenta are generated in non-central heavy ion collisions at high energies. How such huge global angular momenta are transferred to the hot and dense matter created in heavy ion collisions and how to measure them are two core questions in this field. The global polarization is the net polarization of local ones in an event which is aligned in the direction of the event plane. Recently the STAR collaboration has measured the global polarization of Lambda hyperons in the beam energy scan program. At all energies below 62.4 GeV, positive polarizations have been found for Lambda and anti- Lamda .On average over all data, the gobal polarization for Lambda and anti- Lamda are (1.08 +/- 0.15) and (1.38+/- 0.30) respectively. This means that the matter created in ultra-relativistic heavy ion collisions is the most vortical fluid ever produced in the laboratory. A brief overview is given about recent developments in theories and experiments on the global and local spin polarization in heavy ion collisions.
