We have measured, at an average centre-of-mass energy of 34.22 GeV a forward-backward charge asymmetry in the reaction e + e − → μ + μ − of value −0.161 ± 0.032. This demonstrates the existence of an axial vector neutral current with coupling strength of g e a g μ a =0.53 ± 0.10. We have also obtained a limit on the vector coupling strength of g e v g μ v <0.12. The Weinberg angle is found to be sin 2 θ W =0.29 +0.09 −0.11 . From the reaction e + e − → τ + τ − we have found g e a g τ a <0.34, g e v g τ v <0.55.
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Measurements of the tau lepton polarization and forward-backward polarization asymmetry near the Z resonance using the OPAL detector are described. The measurements are based on analyses of tau -> e nu_e nu_tau, tau -> mu nu_mu nu_tau, tau -> pi nu_tau, tau -> rho nu_tau and tau -> a1 nu_tau decays from a sample of 144810 e+e- -> tau+ tau- candidates corresponding to an integrated luminosity of 151 pb-1. Assuming that the tau lepton decays according to V-A theory, we measure the average tau polarization near Ecm = MZ to be <Ptau> = (-14.10 +/- 0.73 +/- 0.55)% and the tau polarization forward-backward asymmetry to be Afb = (-10.55 +/- 0.76 +/- 0.25)%, where the first error is statistical and the second systematic. Taking into account the small effects of the photon propagator, photon-Z interference and photonic radiative corrections, these results can be expressed in terms of the lepton neutral current asymmetry parameters: Atau = 0.1456 +/- 0.0076 +/- 0.0057, Ae = 0.1454 +/- 0.0108 +/- 0.0036. These measurements are consistent with the hypothesis of lepton universality and combine to give Al = 0.1455 +/- 0.0073. Within the context of the Standard Model this combined result corresponds to sin^2(theta)(lept,effective) = 0.23172 +/- 0.00092. Combing these results with those from the other OPAL neutral current measurements yields a value of sin^2(theta)(lept,effective) = 0.23211 +/- 0.00068.
No description provided.
The reaction e + e − → τ + τ − has been measured using the high resolution spectrometer at PEP. The angular distribution shows a forward-backward asymmetry of −(6.1±2.3±0.5)%, corresponding to an axial-vector coupling if g a τ g a e = 0.28 ±0.11± 0.03, in good agreement with the standard model of electroweak interactions. The measured cross section yields ifR ττ = 1.10± 0.03±0.04, consistent with QED and giving QED cutoff parameters of Λ + >92 GeV and Λ − >246 GeV at 95% C.L.
Comparison of total tau pair cross section with O(alpha**3) QED prediction.
Corrected for acceptance backgraound, and O(alpha**3) radiative effects.
Forward-backward asymmetry based on fit to angular distributions.
The e + e − → τ + τ − process has been measured using the CELLO detector at a mean total centre of mass energy of 34.2 GeV using essentially all the decay channels of the τ lepton. The measured cross section yields R τ =1.03±0.05 (stat)±0.07 (syst). Topological branching fraction are given for τ → 1, 3 or 5 charged tracks. The angular distribution shows a clear 1 + cos 2 θ dependance with a forward-backward asymmetry of -0.103 ± 0.052 corresponding to an axial-vector coupling a τ of the τ to the weak neutral current given by a τ =−1.12 ± 0.57.
No description provided.
Forward-backward asymmetry based on 1 + (cos(theta))**2 + bcos(theta) fit for angular distribution.
No description provided.
A high-statistics measurement is presented of the cross section for the process e+e−→τ+τ− at s=29 GeV from the MAC detector at PEP. A fit to the angular distribution of our sample of 10 153 events with |cosθ|<0.9 gives an asymmetry Aττ=−0.055±0.012±0.005 from which we find the product of electron and tau axial-vector weak neutral couplings gAegAτ=0.22±0.05.
Data fully corrected up to O(ALPHA**3) radiative effects. Data requested from authors.
Data extrapolated to full acceptance.
No description provided.
A measurement of theτ lepton polarization and its forward-backward asymmetry at the Z0 resonance using the OPAL detector is described. The measurement is based on analyses of τ→ρντ, ττπ(K)ντ,\(\tau\to e\bar \nu _e \nu _\tau\),\(\tau\to \mu \bar \nu _\mu\nu _\tau\) andτ→a1ντ decays from a sample of 89075 e+e−→τ+τ− candidates corresponding to an integrated luminosity of 117 pb−1. Assuming that theτ lepton decays according to V-A theory, we measure the averageτ polarization at √s=MZ to be 〈P〉=(−13.0±0.9±0.9)% and theτ polarization forward-backward asymmetry to be ApolFB=(−9.4±1.0±0.4)%, where the first error is statistical and the second systematic. These results are consistent with the hypothesis of lepton universality and, when combined, can be expressed as a measurement of sin2θefflept=0.2334±0.0012 within the context of the Standard Model.
No description provided.
The differential cross sections for lepton pair production in e+e− annihilation at 29 GeV have been measured and found to be in good agreement with the standard model of the electroweak interaction. With the assumption of e−μ−τ universality, the weak neutral-current couplings are determined to be ga2=0.23±0.05 and gv2=0.03±0.04.
Numerical values supplied by M.Levi.
Extrapolated to full angular range.
Extrapolated to full angular range.
The$\tau$polarisation has been studied with the${\rm e^+e^-}\to \tau^+\tau^-$data collected by the DELPHI detector at LEP in
The errors are statistical and systematic combined in quadrature.
No description provided.
During the 1992 running period of the LEP e + e − collider, the DELPHI experiment accumulated approximately 24 pb − of data at the Z 0 peak. The decays into hadrons and charged leptons have been analysed to give values for the cross sections and leptonic forward-backward asymmetries which are significantly improved with respect to those previously published by the DELPHI collaboration. Incorporating these new data, more precise values for the Z 0 resonance parameters are obtained from model-independent fits. The results are interpreted within the framework of the Standard Model, yielding for the top quark mass m t = 157 −48 +36 (expt.) −20 +19 (Higgs) GeV, and for the effective mixing angle sin 2 θ eff lept = 0.2328 ± 0.0013 (expt.) −0.0003 +0.0001 (Higgs), where (Higgs) represents the variation due to Higgs boson mass in the range 60 to 1000 GeV, with central value 300 GeV.
No description provided.
First result corresponds to the total cross section (i.e. S+T channel), while second one corresponds to S-channel only. An acollinearity less that 10 deg.
Forward-backward asymmetry within the polar angular range 44 < THETA < 136 degrees and acollinearity < 10 degrees.. First result corresponds to the total cross section (i.e. S+T channel), while second one corresponds to S-channel only.
A study of τ-lepton production in the CMS energy region from 14 to 46.8 GeV at PETRA is reported. The cross section, the decay branching ratio into μν ν , and the electroweak parameters are determined with a total integrated luminosity of 115 pb −1 .
Total cross section calculated from measured channel cross section assuming BR(tau-mu) = 17.6 pct. SIG(Q=MU) is the QED point cross section.
No description provided.
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