# What is the 4-spin vector of a photon?

The photon, being a vector boson has 2 spin states, $\pm 1$.

In relativity, we can determine the four-spin vector $s^{\mu}$ of a particle (see e.g. Costa et al. 2017).

What would $s^{\mu}$ be for a photon? How does it relate to the 2 spin states?

Thanks