First Observation of $\tau\to 3\pi\eta\nu_{\tau}$ and $\tau\to f_{1}\pi\nu_{\tau}$ Decays

TL;DR

This paper reports the first observation of specific tau decay channels involving eta mesons, measuring their branching fractions and identifying substructure, thus expanding understanding of tau decay modes.

Contribution

It presents the first measurements of tau decays to three pions and eta, including evidence for f1 meson involvement, and sets upper limits on eta' production in tau decays.

Findings

Measured branching fractions for tau decays with eta in the final state.

Evidence for f1→ηππ substructure in tau decays.

Set upper limits on eta' production in tau decays.

Abstract

We have observed new channels for $\tau$ decays with an $\eta$ in the final state. We study 3-prong tau decays, using the $\eta\to\gamma\gamma$ and $\eta\to 3\piz$ decay modes and 1-prong decays with two $\piz$'s using the $\eta\to\gamma\gamma$ channel. The measured branching fractions are $\B(\tau^{-}\to \pi^{-}\pi^{-}\pi^{+}\eta\nu_{\tau}) =(3.4^{+0.6}_{-0.5}\pm0.6)\times10^{-4}$ and $\B(\tau^{-}\to \pi^{-}2\piz\eta\nu_{\tau} =(1.4\pm0.6\pm0.3)\times10^{-4}$. We observe clear evidence for $f_1\to\eta\pi\pi$ substructure and measure $\B(\tau^{-}\to f_1\pi^{-}\nu_{\tau})=(5.8^{+1.4}_{-1.3}\pm1.8)\times10^{-4}$. We have also searched for $\eta'(958)$ production and obtain 90% CL upper limits $\B(\tau^{-}\to \pi^{-}\eta'\nu_\tau)<7.4\times10^{-5}$ and $\B(\tau^{-}\to \pi^{-}\piz\eta'\nu_\tau)<8.0\times10^{-5}$.