For the lepton, an explicit list of decay channels has been put together, which includes channels with up to five final-state particles, some of which may be unstable and subsequently decay to produce even larger total multiplicities.
The leptonic decays
where is or , are distributed according to the
standard matrix element
In decays to hadrons, the hadrons and the are distributed according to phase space times the factor , where in the rest frame of the . The latter factor is the spectrum predicted by the parton level matrix element, and therefore represents an attempt to take into account that the should take a larger momentum fraction than given by phase space alone.
The probably largest shortcoming of the decay treatment is that no polarization effects are included, i.e. the is always assumed to decay isotropically. Usually this is not correct, since a is produced polarized in and decays. The PYTAUD routine provides a generic interface to an external decay library, such as TAUOLA [Jad91], where such effects could be handled (see also MSTJ(28)).