Showing papers by "G. Chiefari published in 1994"
01 Dec 1994
259 citations
TL;DR: In this article, the leptonic and hadronic cross sections were measured with the L3 detector at LEP and the results of these measurements were used to determine the electroweak parameters.
Abstract: We report on the measurement of the leptonic and hadronic cross sections and leptonic forward-backward asymmetries at theZ peak with the L3 detector at LEP. The total luminosity of 40.8 pb−1 collected in the years 1990, 1991 and 1992 corresponds to 1.09·106 hadronic and 0.98·105 leptonicZ decays observed. These data allow us to determine the electroweak parameters. From the cross sections we derive the properties of theZ boson:
$$\begin{gathered} M_Z = 91195 \pm 9MeV\Gamma _{\rm Z} = 2494 \pm 10MeV \hfill \\ \Gamma _{had} = 1748 \pm 10MeV\Gamma _\ell = 83.49 \pm 0.46MeV \hfill \\ \end{gathered} $$
assuming lepton universality. We obtain an invisible width of Γinv=496.5±7.9 MeV which, in the Standard Model, corresponds to a number of light neutrino species ofN
v=2.981±0.050. Using also the three leptonic forward-backward asymmetries and the average tau polarization, we determine the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons to be:
$$\bar g^\ell v = - 0.0378_{ - 0.0042}^{ + 0.0045} \bar g^\ell _A = - 0.4998 \pm 0.0014.$$
Within the framework of the Standard Model, and including our measurements of the
$$Z \to b\bar b$$
forward-backward asymmetry and partial decay width, we derive an effective electroweak mixing angle of
$$sin^2 \bar \theta _W = 0.2326 \pm 0.0012$$
. We obtain an estimate for the strong coupling constant, αS=0.142 ± 0.013 and for the top-quark mass,m
t
=158
−40
+32
±19(Higgs) GeV, where the second error arises due to the uncertainty in the Higgs-boson mass.
34 citations
TL;DR: In this paper, the authors measured the polarization of τ-leptons as a function of the production polar angle using the following 1-prong τ decay modes: τ − → e − v e v τ, τ− →π − (K − )v τ, τ − − →ϱ − v τ and τ −→a 1 − vτ, and obtained for the ratio vector to axial-vector weak neutral couplings for electrons gVe/gAe=0.0791± 0.0099(stat)±0.
25 citations
TL;DR: Using the L3 detector, the branching ratio BR(b → πνX) has been measured using a sample of Z → b b events tagged by high momentum and high transverse momentum leptons in one hemisphere and with missing energy in the opposite hemisphere as mentioned in this paper.
20 citations
TL;DR: In this article, the authors measured the time integrated B0 B 0 mixing parameter and the forward-backward asymmetry in the process e+e− → b b using hadronic events containing muons or electrons.
14 citations
TL;DR: In this article, the authors studied the four-fermion processes ee → eeee, eeμμ, eebττ, μμμm, eeqq, and μμqq with the L3 detector at LEP.
10 citations
02 Aug 1994
TL;DR: In this article, the branching fractions for the hadronic τ decays, τ → π K nπ° ν (0≤ n ≤ 3), with the L3 detector at LEP.
Abstract: Abstract We have measured the branching fractions for the hadronic τ decays, τ → π K nπ° ν (0≤ n ≤3), with the L3 detector at LEP. Multiphoton final states are analyzed using the fine-grained, high-resolution electromagnetic calorimeter. The decay channels are identified using a neural network method. The results are: BR (τ → π K ν ) = (11.82 ± 0.26 ± 0.43) %, BR (τ → π K π° ν) = (25.05 ± 0.35 ± 0.50) %, BR (τ → π K 2π° ν) = (8.88 ± 0.37 ± 0.42) %, BR (τ → π K 3πδ ν) = (1.70 ± 0.24 ± 0.38) %, where the first error quoted is statistical, the second systematic.
1 citations