Precision Measurements of Tau Lepton Decays

Using data collected with the BABAR detector at the SLAC PEP-II electron-positron storage ring operating at a centre-of-mass energy near 10.58 GeV, the branching fractions B(τ- → π-π-π+ντ) =(8.83±0.01±0.13)%, B(τ- → K-π-π+ντ) =(0.273± 0.002 ± 0.009)%, B(τ- → K-π-K+ντ) =(0.1346 ± 0.0010 ± 0.0036)%, and B(τ- → K-K-K+ντ) =(1.58 ± 0.13 ± 0.12) × 10-5 are measured where the uncertainties are statistical and systematic, respectively. The invariant mass distribution for the τ- → π-π-π+ντ , τ- → K-π-π+ντ , τ- → K-π-K+ντ and τ- → K-K-K+ντ decays are unfolded to correct for detector effects. A measurement of B(τ- → φπ-ντ ) =(3.42±0.55±0.25)×10-5, a measurement of B(τ- → φK-ντ) =(3.39±0.20±0.28)× 10-5 and an upper limit on B(τ- → K-K-K+ντ [ex.φ]) ≤ 2.5 × 10-6@90%CL are determined from a binned maximum likelihood fit of the τ- → K-π-K+ντ and τ- → K-K-K+ντ K+K- invariant mass distributions. The branching ratio B(τ-→K-ντ )/ B(τ-→π-ντ ) is measured to be (6.531±0.056±0.093)×10-2 from which |Vus| is determined to be 0.2255 ± 0.0023. The branching ratio B(τ-→μ-ντ $\bar{v}$μ)/ B(τ-→e-ντ $\bar{v}$e) =(9.796 ± 0.016 ± 0.035) × 10-1 is measured enabling a precision test of the Standard Model assumption of charged current lepton universality, gμ ge =1.0036 ± 0.0020. The branching ratios B(τ-→K-ντ ) /B(τ-→e-ντ $\bar{v}$e) =(3.882 ± 0.032 ± 0.057) × 10-2, and B(τ-→π-ντ ) /B(τ-→e-ντ $\bar{v}$e) =(5.945 ± 0.014 ± 0.061) × 10-1 are measured which provide additional tests of charged current lepton universality, gτ/gμ π = 0.9856 ± 0.0057 and gτ/gμ K = 0.9827 ± 0.0086 which can be combined to give gτ/gμ π/K = 0.9850 ± 0.0054 . Any deviation of these measurements from the expected Standard Model values would be an indication of new physics.

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