  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.
