Tau decays involving η and τ → f1πν τ from CLEO

Abstract

We present a new measurement of the τ − → h − π 0 ην τ decay parameters which includes the most precise calculation of the B ( τ − → h − π 0 ην τ ) branching fraction and comparison with CVC predictions. We have found a new channel for tau decays with a neutrino, 3 charged hadrons and η in the final state. An observation is made in 3-prong tau decays where the η is reconstructed from its η → γγ and η → 3 π 0 decays. The measured branching fraction B ( τ − → h − h + h − ην τ ) = (4.3 ± 0.8 ± 0.8) · 10 −4 is about two orders of magnitude larger than the theoretical prediction. The hadronic final state exhibits a substructure with clear evidence of a significant f 1 (1285) production. The corresponding decay branching fraction is B ( τ − → f 1 π − ν τ ) = (6.8 ± 1.8 ± 2.4) · 10 −4 , measured from the f 1 → ηπ + π − and f 1 → ηπ 0 π 0 decay modes. A corroborating signal for f 1 (1285) production is found also in other tau decay modes. For the first time we have set upper limits for the branching fractions B ( τ → h 5 π 0 ν τ ), B ( τ → hη ′(958) ν τ ) and B ( τ → hπ 0 η ′(958) ν τ ).