Axial vector and pseudoscalar hadronic structure in tau decays to three charged pions and a tau neutrino with implications on light quark masses
Abstract
After a survey of the basic concepts in high energy physics, a model-dependent analysis of the substructure in τ± → π ±π±π∓( ντ/ντ) decays is presented. The analysis is based on 145,000 decays skimmed from a sample of 4.3 × 106 e+e − → τ+τ− events collected by the CLEO II detector operating at the CESR collider. The hadronic transition current in the τ± → π ±π±π∓( ντ/ντ) decay is described by modeling the axial vector a1(1260) and pseudoscalar π ′(1300) primary resonances and their sub-resonances. An unbinned maximum likelihood fit is used to extract the complex amplitude for each sub-resonance, producing a distribution that accounts well for the data. Two model variations are also considered, including one in which corrections due to a more general chiral limit induce pseudoscalar-like terms from the axial vector components and introduce a non-resonant term. All models are found to reasonable describe the data. As expected, the decay is found to be dominated by s-wave a1 → ρπ, which contributed around 70–75% of the τ± → π±π ±π∓(ν τ/ντ) rate, depending on the model used. Statistically significant contributions are also found for d-wave ρπ and ρ′π amplitudes as well as amplitudes involving isoscalars, f2(1270), π, σπ, and f0(1270)π. The isoscalar contributions are particularly prominent, as are interferences involving those terms. As a whole, they contributed around 15–17% to the total τ± → π ±π±π∓( ντ/ντ) rate, depending on the model. Contributions from the pseudoscalar π′ sub-resonances are generally statistically insignificant, though their minimal improvements are shown to lie where one would expect. Upper limits are placed on each of the considered π′ contributions at 90% confidence. The results found for the pseudoscalar contributions are used to place a lower limit on the average of the up and down quark running masses [mˆ ≡ (mu + md)/2] that appear in the QCD Lagrangian [57]. This produced a 90% confidence limit of mˆ(1 GeV2) > 8.3 − 14.2 MeV, depending on the model. Though that result may be higher than expected, it is reasonable given the particulars of the analysis.
Degree
Ph.D.
Advisors
Shibata, Purdue University.
Subject Area
Particle physics
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