TTP06-01 Tau-Decays to Five Mesons in TAUOLA

The $\tau$-decay library TAUOLA has gained popularity over the last decade. However, with the continuously increasing precision of the data, some of its functionality has become insufficient. One of the requirements is the implementation of decays into five mesons plus a neutrino with a realistic decay amplitude. This note describes a step into this direction. For the $2\pi^-\pi^+2\pi^0$ mode the three decay chains $\tau^- \to a_1^- \nu \to \rho^-(\to \pi^-\pi^0) \omega (\to \pi^-\pi^+\pi^0) \nu$, $\tau^- \to a_1^- \nu \to a_1^-(\to 2\pi^-\pi^+) f_0 (\to 2\pi^0) \nu$, and $\tau^- \to a_1^- \nu \to a_1^-(\to \pi^-2\pi^0) f_0 (\to \pi^+\pi-) \nu$ are introduced with simple assumptions about the couplings and propagators of the various resonances. Similar amplitudes (without the $\rho\omega$ contributions) are adopted for the $\pi^-4\pi^0$ and $3\pi^-2\pi^+$ modes.

The five-pion amplitude is thus based on a simple model, which, however, can be considered as a first realistic example. Phase-space generation includes the possibility of presampling the $\omega$ and $a_1$ resonances, in one channel only, however. This is probably sufficient for the time being, both for physics applications and for tests.

The technical test of the new part of the generator is performed by comparing Monte Carlo and analytical results. To this end a non-realistic, but easy to calculate, purely scalar amplitude for the decay into five massless pions was used.