# Magnetic Field Induced Polarization Difference between Hyperons and Anti-hyperons

## TL;DR

This paper explores how in-medium magnetic fields during heavy-ion collisions can cause polarization differences between hyperons and anti-hyperons, using the AMPT model to analyze magnetic field effects across various energies.

## Contribution

It provides a phenomenological analysis of magnetic field effects on hyperon polarization differences, estimating magnetic field lifetimes consistent with experimental data.

## Key findings

- Polarization difference is highly sensitive to magnetic field lifetime.
- Computed differences depend mildly on magnetic field evolution details.
- Magnetic field lifetime scales inversely with collision energy.

## Abstract

Recent STAR measurements suggest a difference in the global spin polarization between hyperons and anti-hyperons, especially at relatively low collision beam energy. One possible cause of this difference is the potential presence of in-medium magnetic field. In this study, we investigate the phenomenological viability of this interpretation. Using the AMPT model framework, we quantify the influence of different magnetic field evolution scenarios on the size of the polarization difference in a wide span of collision beam energies. We find that such difference is very sensitive to the lifetime of the magnetic field. For the same lifetime, the computed polarization difference only mildly depends on the detailed form of its evolution. Assuming magnetic polarization as the mechanism to enhance anti-hyperon signal while suppress hyperon signal, we phenomenologically extract an upper limit on the needed magnetic field lifetime in order to account for the experimental data. The so-obtained lifetime values are in a quite plausible ballpark and follow approximately the scaling relation of being inversely proportional to the beam energy. Possible implications on other magnetic field related effects are also discussed.