The spin alignment of vector mesons with light front quarks

TL;DR

This paper uses the light front framework to explain the observed spin alignment of vector mesons in heavy ion collisions, highlighting the importance of orbital angular momentum and gluon interactions in this phenomenon.

Contribution

The study introduces a light front approach to describe hadron spin, successfully explaining the spin alignment of vector mesons and matching experimental data.

Findings

The light front spinor naturally explains polarization with $ ho_{00}>1/3$.

The model's predictions for $ ho$ mesons agree with experimental results.

Orbital angular momentum and gluon interactions are crucial for spin alignment.

Abstract

The global spin alignment of the vector meson has been observed in relativistic heavy ion collisions, but is still on hot debates in the theoretical community. Here we propose to apply the light front framework to explain this phenomenon since the light front form explicitly describes the hadron spin including both the quark spin and the orbital angular momentum. After applying the light front spinor, we find that the spin alignment in the polarization of vector mesons with $\rho_{00}>1/3$ can be naturally manifested and in particular, the obtained spin alignment for $\phi$ meson is in good agreement with the experimental data. This implies that to explain the spin alignment it is important to properly include the contribution from the gluon interactions that are presented in terms of the orbital angular momentum of the hadron bound state.