Abstract This chapter addresses the case of a vector particle produced indirectly from decay or transformation having $$J = 0$$ ( $$\chi_{c0} \to \mathrm{J}/\psi \, \gamma$$ , $$\mathrm{B} \mathrm{K}$$ $$\mathrm{H} \mathrm{Z} etc.), 1$$ 2$$ $$\chi_{c1,2} $$\mathrm{Z} describing polarization frame definitions that can be adopted to represent two-step process, and their respective advantages. We ...