Precision Measurements of Tau Lepton Decays

Thesis/Dissertation · Tue Jan 01 00:00:00 EST 2008

DOI:https://doi.org/10.2172/969233· OSTI ID:969233

Nugent, Ian M. ^[1]

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1. Univ. of Victoria, BC (Canada)

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^-ν_τ )/ B(τ^-→π^-ν_τ ) 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^-ν_τ $$\bar{v}$$_μ)/ B(τ^-→e^-ν_τ $$\bar{v}$$_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^-ν_τ ) /B(τ^-→e^-ν_τ $$\bar{v}$$_e) =(3.882 ± 0.032 ± 0.057) × 10^-2, and B(τ^-→π^-ντ ) /B(τ^-→e^-ν_τ $$\bar{v}$$_e) =(5.945 ± 0.014 ± 0.061) × 10^-1 are measured which provide additional tests of charged current lepton universality, g_τ/g_{μ π} = 0.9856 ± 0.0057 and g_τ/g_{μ K} = 0.9827 ± 0.0086 which can be combined to give g_τ/g_{μ π/K} = 0.9850 ± 0.0054 . Any deviation of these measurements from the expected Standard Model values would be an indication of new physics.

• Research Organization: SLAC National Accelerator Lab., Menlo Park, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-76SF00515
• OSTI ID: 969233
• Report Number(s): SLAC-R-936; TRN: US1000264
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
ACCURACY
BRANCHING RATIO
CHARGED CURRENTS
LEPTONS
MASS DISTRIBUTION
MAXIMUM-LIKELIHOOD FIT
PHYSICS
STANDARD MODEL
STANFORD LINEAR ACCELERATOR CENTER
STORAGE RINGS
TAU PARTICLES
Experiment-HEP
HEPEX