Resonance Decays

Resonances (see section ) can be made to decay in two different routines. One is the standard decay treatment (in PYDECY) that can be used for any unstable particle, where decay channels are chosen according to fixed probabilities, and decay angles usually are picked isotropically in the rest frame of the resonance, see section . The more sophisticated treatment (in PYRESD) is the default one for resonances produced in PYTHIA, and is described here. The ground rule is that everything in mass up to and including $\b$ hadrons is decayed with the simpler PYDECY routine, while heavier particles are handled with PYRESD. This also includes the $\gamma^* / \mathrm{Z}^0$, even though here the mass in principle could be below the $\b$ threshold. Other resonances include, e.g., $\t$, $\mathrm{W}^{\pm}$, $\mathrm{h}^0$, $\mathrm{Z}'^0$, $\mathrm{W}'^{\pm}$, $\H ^0$, $\mathrm{A}^0$, $\H ^{\pm}$, and technicolor and supersymmetric particles.