Measurement of the $\tau \to \eta \pi \pi^{degree} \nu_{\tau}$ branching ratio using $\eta \to \gamma \gamma$ and $\eta \to \pi^{+}\pi^{-} \pi^{0}$ final states

Using Aleph data until 1993, the branching ratio of the $\tau$ into $\eta\pi\pi^0$ has been measured using the $\eta\rightarrow \gamma\gamma$ decay. We have separated the signal from a large $\pi^0$ background by anti-tagging it and fitted the eta proportion in the remaining two photons invariant mass spectra. We see compatible contributions in 2 samples: one with 3 photons in which we fit the eta peak in one dimension, the other with 4 photons where we look for a two dimensional $(\eta,\pi^0)$ signal.