UC Irvine

The branching fractions for the major decay modes of the τ lepton are measured from a sample of tagged τ decays selected from τ+τ- pairs produced in e+e- annihilation. The decay products of one member of the τ+τ- pair are used to identify the event. The opposite member of the pair is then included in the sample if it satisfies an invariant-mass cut and a charged-multiplicity cut. In this way, we attempt to select an unbiased sample of τ decays. The sample is divided into categories based on charged- and neutral-particle multiplicities, and charged-particle identification. The branching fractions are measured simultaneously, with an unfold technique and a maximum-likelihood fit, with the sum of the branching fractions constrained to be unity. The branching fractions for the decay modes τ-→ντ K- and τ-→ντ K*- are fixed at the world averages in the fit. The following branching fractions are measured: B(τ-→ντe-ν¯e) =(19.1±0.8±1.1)%, B(τ-→ντ μ- ν¯μ)=(18.3±0.9±0.8)%, B(τ-→ντπ-) =(10.0±1.1 *1,4)%, B(τ-→ντπ-π0) =(25.8±1.7±2.5)%, B(τ-→ντπ-(nπ0, n>1))=(12.0±1.4±2.5)%, B(τ-→ντπ-π+π-) =(6.7 ±0.8±0.9)%, and B(τ-→ντπ-π+π- (nπ0,n>0) )=(6.1±0.8±0.9)%. The total branching fraction to one charged pion plus at least one neutral hadron is measured to be (37.8±1.2±1.0)%. Limits on allowed decay modes involving the η meson are discussed.