Measurement of the tau -> 3pi eta nu Branching Fraction and a Search for a Second-Class Current in the tau -> eta'(958) pi nu Decay

TL;DR

This paper measures the tau decay branching fractions involving eta and 3pi, identifies the dominant decay mode, and sets an upper limit on a second-class current decay involving eta' using BaBar data.

Contribution

It provides the first precise measurement of the tau -> 3pi eta nu branching fraction and sets a new upper limit on the forbidden tau -> eta' pi nu decay.

Findings

Branching fraction for tau -> 3pi eta nu is (1.60±0.05±0.11)×10^-4.

Dominant decay mode is tau -> f1 pi nu with a branching fraction of (1.11±0.06±0.05)×10^-4.

Upper limit for tau -> eta'(958) pi nu decay is 7.2×10^-6 at 90% CL.

Abstract

The "\tau\to 3\pi\eta\nu" decay with the "\eta \to \gamma\gamma" mode is studied using 384 fb^-1 of data collected by the BaBar detector. The branching fraction is measured to be (1.60+/-0.05+/-0.11)x10^-4. It is found that "\tau \to f1 \pi \nu to 3\pi \eta \nu" is the dominant decay mode with a branching fraction of (1.11+/-0.06+/-0.05)x10^-4. The first error on the branching fractions is statistical and the second systematic. In addition, a 90% confidence level upper limit on the branching fraction of the "\tau \to \eta'(958) \pi \nu" decay is measured to be 7.2x10^-6. This last decay proceeds through a second-class current and is expected to be forbidden in the limit of isospin symmetry.