Vector meson spin alignments in high energy reactions

The global vector meson spin alignment has been reported recently by the STAR Collaboration at the Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Laboratory (BNL). The results not only show that the global polarization effect in non-central heavy ion collisions also exhibits itself in vector meson polarization but also reveal that strong quark spin correlations may exist in the quark matter system, the quark gluon plasma (QGP), produced in the collision processes thus provide new insights in properties of QGP. It shows in particular that the vector meson spin alignment provides a unique opportunity to study the quark spin correlation in the system. Besides the global spin alignment, vector meson spin alignments in the helicity basis have been also observed in many other high energy reactions such as e^+e^-, e^-p and pp collisions many years ago. The results seem to depend strongly on the hadronization mechanism and comprehensive studies become desiring and necessary. The aim of this invited contribution is to present a brief summary of available experimental data and theoretical results in different hadronization mechanisms to stimulate future comprehensive studies.