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In the particle data group table: http://pdg.lbl.gov/2020/tables/rpp2020-sum-leptons.pdf ,only $\tau \rightarrow \pi + \nu_{\tau}$ is documented. But does $\tau \rightarrow \rho + \nu_{\tau}$ as well? I don't see any conservation laws that could forbid such decay to happen.

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  • $\begingroup$ The decay to the $\rho$ will be phase space suppressed by the heavy $\rho$ mass $\endgroup$ – InertialObserver Jul 6 '20 at 17:48
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The $\rho$ has the quantum numbers of $\pi\pi$ coupled to $I=1$. If they only list particles stable under the strong interaction then $\tau^-\to\rho^-\nu$ is the same as $\tau^-\to\pi^-\pi^0\nu$, which indeed has a branching ratio of 25%. The table is more helpful than that: It lists the non-resonant (non $\rho$) part of $\tau\to \pi^-\pi^0\nu$, which is very small. So the branching ratio is about 25%.

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  • $\begingroup$ Thanks Thomas! Exactly what Im looking for! $\endgroup$ – Andy133 Jul 6 '20 at 22:38

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