In this paper an investigation of the production of D ∗ ± mesons produced in e + e − collisions at energies around the Z 0 pole is presented. Based on 115 D ∗ ± mesons with x D∗ 2E D ∗ /E cm > 0.2 the properties of D ∗ mesons produced in the reaction Z 0 → c c are studied. Fixing the yield and the fragmentation function of bottom quarks to the values obtained at LEP using lepton tags, and average energy fraction of the D ∗ ± mesons from primary charmed quarks of 〈x c → D ∗ 〉 = 0.52 ± 0.03 +- 0.01 is found and Γ z 0 →c c = (323 ± 61 ± 35) MeV is determined. The first error is the combined statistical and systematic error from this experiment, and the second the total error from other sources.
FD denotes the fraction of D* mesons from primary charmed quarks, derived from the fit (see text).
No description provided.
We report on measurements of the triple-gauge-boson couplings of the W boson in e+e- collisions with the L3 detector at LEP. W-pair, single-W and single-photon events are analysed in a data sample corresponding to a total luminosity of 76.7 pb^{-1} collected at centre-of-mass energies between 161 GeV and 183 GeV. CP-conserving as well as both C- and P-conserving triple-gauge-boson couplings are determined. The results, in good agreement with the Standard-Model expectations, confirm the existence of the self coupling among the electroweak gauge bosons and constrain its structure.
The errors are statistical. Two-parameter fit.
The errors are statistical. Two-parameter fit.
The errors are statistical. Two-parameter fit.
We have measured the cross section for e + e − →hadrons over the center of mass energy range of the Z 0 peak, from 88.22 to 95.03 GeV. We determine the Z 0 mass M z =91.164±0.013 (experiment) ±0.030 (LEP) GeV. Within the framework of the standard model we determine the invisible width, Γ invisible =0.502±0.018 GeV, and the number of light neutrino species, N ν =3.01±0.11. We exclude the existence of a supersymmetric scalar neutrino having a mass less than 31.4 GeV, at the 95% confidence level. We performed a model independent combined fit to the e + e − →hadrons and e + e − → μ + μ − data to determine total width, leptonic width and hadronic width of the Z 0 .
Cross sections from 1990 data. Additional systematic error 1.5 pct.
Cross sections from 1989 data. This data has been rescaled by 0.96 from original publication PL B237 (90) 136. Additional systematic error 2.0 pct.
We have measured the partial width and forward-backward charge asymmetry for the reaction e + e - →Z 0 →μ + μ - (γ). We obtain a partial width Γ μμ of 83.3±1.3(stat)±0.9(sys) MeV and the following values for the vector and axial vector couplings: g v =−0.062 −0.015 +0.020 and g A =−0.497 −0.005 +0.005 . From our measurement of the partial width and the mass of the Z 0 boson we determine the effective electroweak mixing angle, sin 2 θ w =0.232±0.005, and the neutral current coupling strength parameter, ϱ =0.998±0.016.
No description provided.
Forward backward charge asymmetry.
No description provided.
The couplings of the Z 0 to charged leptons are studied using measurements of the lepton pair cross sections and forward-backward asymmetries at centre of mass energies near to the mass of the Z 0 . The data are consistent with lepton universality. Using a parametrisation of the lepton pair differential cross section which assumes that the Z 0 has only vector and axial couplings to leptons, the charged leptonic partial decay width of the Z 0 is determined to be Г ol+ol− = 83.1±1.9 MeV and the square of the product of the effective axial vector and vector coupling constants of the Z 0 to charged leptons to be a ̌ 2 ol v ̌ 2 ol = 0.0039± 0.0083 , in agreement with the standard model. A parametrisation in the form of the improved Born approximation gives effective leptonic axial vector and vector coupling constants a ̌ 2 ol = 0.998±0.024 and v ̌ 2 ol = 0.0044±0.0083 . In the framework of the standard model, the values of the parameters ϱ z and sin 2 θ w are found to be 0.998±0.024 and 0.233 +0.045 −0.012 respectively. Using the relationship in the minimal standard model between ϱ z and sin 2 θ w , the results sin 2 θ SM w = 0.233 +0.007 −0.006 is obtained. Our previously published measurement of the ratio of the hadronic to the leptonic partial width of the Z 0 is update: R z = 21.72 +0.71 −0.65 .
Cross sections corrected for the effects of efficiency and kinematic cuts. Errors have systematic effects folded.
Acceptance corrected cross sections. Statistical errors only.
Acceptance corrected cross sections. Statistical errors only.
We present a study of energy-energy correlations based on 83 000 hadronic Z 0 decays. From this data we determine the strong coupling constant α s to second order QCD: α s (91.2 GeV)=0.121±0.004(exp.)±0.002(hadr.) −0.006 +0.009 (scale)±0.006(theor.) from the energy-energy correlation and α s (91.2 GeV)=0.115±0.004(exp.) −0.004 +0.007 (hadr.) −0.000 +0.002 (scale) −0.005 +0.003 (theor.) from its asymmetry using a renormalization scale μ 1 =0.1 s . The first error (exp.) is the systematic experimental uncertainly, the statistical error is negligible. The other errors are due to hadronization (hadr.), renormalization scale (scale) uncertainties, and differences between the calculated second order corrections (theor.).
Statistical errors are equal to or less than 0.6 pct in each bin. There is also a 4 pct systematic uncertainty.
ALPHA_S from the EEC measurement.. The first error given is the experimental error which is mainly the overall systematic uncertainty: the first (DSYS) error is due to hadronization, the second to the renormalization scale, and the third differences between the calculated and second order corrections.
ALPHA_S from the AEEC measurement.. The first error given is the experimental error which is mainly the overall systematic uncertainty: the first (DSYS) error is due to hadronization, the second to the renormalization scale, and the third differences between the calculated and second order corrections.
The cross section of the pure QED process e + e − → γγ has been measured using data accumulated during the 1989 and 1990 scans of the Z 0 resonance at LEP. Both the energy dependence and the angular distribution are in good agreement with the QED prediction. Upper limits on the branching ratios of Z 0 → γγ , Z 0 → π 0 γ and Z 0 → ηγ have been set at 1.4×10 −4 , 1.4×10 −4 and 2.0×10 −4 respectively. Lower limits on the cutoff parameters of the modified electron propagator have been found to be Λ + > 117 GeV and Λ − > 110 GeV. The reaction e + e − → γγγ has also been studied and was found to be consistent with the QED prediction. An upper limit on the branching ratio of Z 0 → γγγ has been set at 6.6 × 10 −5 . All the limits are given at 95% confidence level.
No description provided.
No description provided.
No description provided.
We present a study of jet multiplicities based on 37 000 hadronic Z 0 boson decays. From this data we determine the strong coupling constant α s =0.115±0.005 ( exp .) −0.010 +0.012 (theor.) to second order QCD at √ s =91.22GeV.
Errors are combined statistical and systematic uncertainties.
No description provided.
We have measured the cross-section of the reaction e + e − → γγ at center of mass energies around the Z 0 mass. The results are in good agreement with QED predictions. For the QED cutoff parameters the limit of Λ + > 103 GeV and Λ − 118 GeV are found. For the decays Z 0 → γ ,Z 0 → π 0 γ , Z 0 → γγγ we find upper limits of 2.9 × 10 −4 ,2.9×10 −4 ,4.1×10 −4 and 1.2×10 −4 , respectively. All limits are at 95% CL.
No description provided.
We have measured the partial widths for the three reactions e + e − → Z 0 → e + e − , μ + μ − , τ + τ − . The results are Γ ee = 84.3±1.3 MeV, √ Γ ee Γ μμ =83.9±1.4 MeV, and √ Γ ee Γ ττ =83.9±1.4 MeV, where the errors are statistical. The systematic errors are estimated to be 1.0 MeV, 0.9 MeV, and 1.4 MeV, respectively. We perform a simultaneous fit to the cross sections for the e + e − →e + e − , μ + μ − , and τ + τ − data, the differential cross section as a function of polar angle for the electron data, and the forward- backward asymmetry for the muon data. We obtain the leptonic partial with Γ ℓℓ =84.0±0.9 (stat.) MeV. The systematic error is estimated to be 0.8 MeV. Also, we obtain the axial-vector and vector weak coupling constants of charged leptons, g A =−0.500±0.003 and g ν =−0.064 −0.013 +0.017 .
Cross section from 1990 data.
Visible cross section obtained using the cuts required by Method I (see text of paper). (1989 and 1990 data).
Visible cross section obtained using the cuts required by Method II (see text of paper). (1989 and 1990 data). RE = E+ E- --> E+ E- (GAMMA).
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