Vector meson's spin alignments in high energy reactions

TL;DR

This paper reviews the experimental and theoretical progress in understanding the spin alignment of vector mesons across various high-energy collisions, highlighting the influence of different hadronization mechanisms on observed phenomena.

Contribution

It provides a comprehensive overview of recent advances in studying vector meson spin alignments, emphasizing the role of hadronization processes in different collision environments.

Findings

Spin alignment observed in heavy ion collisions linked to quark coalescence.

Different spin alignment patterns in $e^+e^-$ annihilations suggest varied hadronization mechanisms.

Theoretical models are being developed to explain the dependence on hadronization processes.

Abstract

The global spin alignment of vector mesons has been observed by the STAR collaboration at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). It provides a unique opportunity to probe the correlation between the polarized quark and antiquark in the strongly coupled quark-gluon plasma (sQGP) produced in relativistic heavy ion collisions, opening a new window to explore the properties of sQGP. In addition, spin alignments of vector mesons have also been observed in other high-energy particle collisions such as $e^+e^-$ annihilations at high energies where hadron production is dominated by quark fragmentation mechanism. The results obtained are quite different from those obtained in heavy ion collisions where quark coalescence/combination mechanism dominates suggesting strong dependence on hadronization mechanisms. So comprehensive studies in different hadronization processes are needed. In this article, we present a brief review of theoretical and experimental advances in the study of vector meson's spin alignments in a variety of high-energy particle collisions, with emphasis on hadronization mechanisms.