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### Strong and electromagnetic decays

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

 (271)

is used, with the the pion momenta in the rest frame of the decay. (Actually, what is coded is the somewhat more lengthy Lorentz invariant form of the expression above.)

Consider the decay chain , with representing pseudoscalar mesons and a vector one. Here the decay angular distribution of the in its rest frame is

 (272)

where is the angle between and . The classical example is . If the is replaced by a , the angular distribution in the decay is instead .

In Dalitz decays, or , the mass of the pair is selected according to

 (273)

The last factor, the VMD-inspired propagator, is negligible for decay. Once the has been selected, the angular distribution of the pair is given by
 (274)

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.

Next: Weak decays of the Up: Decays Previous: Decays   Contents
Stephen Mrenna 2007-10-30