Angular distributions of radiative quarkonium cascade decays into three particles are presented, using the helicity formalism. These three particles can be either three pseudoscalar mesons or a lepton-antilepton pair and a pseudoscalar meson. Three-meson final states also occur in two-body sequential decays when the intermediate state $\chi$ formed in the radiative decay of quarkonium subsequently decays into a meson resonance decaying into a meson pair, along with a third meson. Inferences on the spins and parties of the intermediate $\chi$ are made.

• Received 13 June 1989

DOI:https://doi.org/10.1103/PhysRevD.40.3641