The decays of hadrons containing the `ordinary' , and quarks into two or three particles are known, and branching ratios may be found in [PDG96]. (At least for the lowest-lying states; the four meson multiplets are considerably less well known.) We normally assume that the momentum distributions are given by phase space. There are a few exceptions, where the phase space is weighted by a matrix-element expression, as follows.
In and decays to
, a matrix element
of the form
Consider the decay chain
with representing pseudoscalar mesons and a vector one. Here
the decay angular distribution of the in its rest frame is
In Dalitz decays, or
, the mass
pair is selected according to
Also a number of simple decays involving resonances of heavier hadrons, e.g. or are treated in the same way as the other two-particle decays.