  The di-fermion angular distribution observed in decays of inclusively
produced vector particles is characterized by two frame-independent
observables, reflecting the average spin-alignment of the produced particle and
the magnitude of parity violation in the decay. The existence of these
observables derives from the rotational properties of angular momentum
eigenstates and is a completely general result, valid for any J=1 state and
independent of the production process. Rotation-invariant formulations of
polarization and of the decay parity-asymmetry can provide more significant
measurements than the commonly used frame-dependent definitions, also improving
the quality of the comparisons between the measurements and the theoretical
calculations.
