Measurement of the τ-→f1(1285)π-ντ branching fraction and a search for second-class currents in τ→η'(958)π-ντ

The τ-→ηπ-π+π-ντ decay with the η→γγ 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 τ-→f1(1285)π-ντ→ηπ-π+π-ντ is the dominant decay mode with a branching fraction of (1.11±0.06±0.05)x10-4. The first error is statistical and the second systematic. In addition, a 90% confidence level upper limit on the branching fraction of the τ-→η'(958)π-ντ 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.