Polarization in Cascade Decays

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} $$\mathrm{Z} describing polarization frame definitions that can be adopted to represent two-step process, and their respective advantages. We illustrate how several measurement kinematic conditions lead very different observable polarizations particle, in special but frequent where intermediate step remains unobserved only final dilepton angular distribution is measured. also discuss peculiar observation, made at LHC, almost unpolarized “directly” J/ $$\psi$$ mesons may understood as result production mechanism.