Reference frame of the polarization vector

[simonthor]

I am using GENIE v3.4 and using the polarization vector (retrieved via GHepParticle.GetPolarization(), or from the StdHepPolz branch in rootracker files).
Is this vector given in the lab frame or the particle rest frame? In other words, does a polarization vector of (0,0,1) mean that the spin vector is aligned with the tau momentum or the lab frame z axis?
I tried looking through the GENIE physics and user manual but could not find any answer to this.