The hadronic lineshape of the Z has been analyzed for evidence of signals of new, narrow vector resonances in the Z-mass range. The production rate of such resonances would be enhanced due to mixing with the Z. No evidence for new states is found, and it is thus possible to exclude, at the 95% confidence level, a quarkonium state in the mass range from 87.7 to 94.7 GeV.
Statistical errors only.
We report on a measurement of the processes e + e − →e + e − , e + e − → μ + μ − , and e + e − → τ + τ − near the Z 0 pole. On the basis of 163 e + e − , 101 μ + μ − and 87 τ + τ − events we obtain Γ ee =89±4±4 MeV, Γ μμ =85±9±6 MeV and Γ ττ =87±10±8 MeV, compatible with the standard model. Combining these with our previous results on hadronic Z 0 decays, we find a hadronic width Γ had =1787±81±90 MeV and an invisible width Γ inv =552±85±71 MeV.
Statistical errors only.
Statistical errors only.
Relative production rates of multijet hadronic final states of Z 0 boson decays, observed in e + e − annihilation around 91 GeV centre of mass energy, are presented. The data can be well described by analytic O( α s 2 ) QCD calculations and by QCD shower model calaculations with parameters as determined at lower energies. A first judgement of Λ MS and of the renormalization scale μ 2 in O( α s 2 ) QCD results in values similar to those obtained in the continuum of e + e − annihilations. Significant scaling violations are observed when the 3-jet fractions are compared to the corresponding results from smaller centre of mass energies. They can be interpreted as being entirely due tot the energy dependence of α s , as proposed by the nonabelian nature of QCD, The possibility of an energy independent coupling constant can be excluded with a significance of 5.7 standard deviations.
Data are corrected for final acceptance and resolution of the detector. No explicit corrections for hadronisation effects are applied.
We report an experimental determination of the cross section for e + e − → hadrons from a scan around the Z 0 pole. On the basis of 4350 hadronic events collected over seven energy points between 89.26 GeV and 93.26 GeV we obtain a mass of m z =91.01±0.05±0.05 GeV, and a total decay width of Γ z =2.60±0.13 GeV. In the context of the standard model t these results imply 3.1 ± 0.4 neutrino generations.
No description provided.
The search for an additional heavy gauge boson Z′ is described. The models considered are based on either a superstring-motivated E 6 or on a left-right symmetry and assume a minimal Higgs sector. Cross sections and asymmetries measured with the L3 detector in the vicinity of the Z resonance during the 1990 and 1991 running periods are used to determine limits on the Z-Z′ gauge boson mixing angle and on the Z′ mass. For Z′ masses above the direct limits, we obtain the following allowed ranges of the mixing angle, θ M at the 95% confidence level: −0.004 ⪕ θ M ⪕ 0.015 for the χ model, −0.003 ⪕ θ M ⪕ 0.020 for the ψ model, −0.029 ⪕ θ M ⪕ 0.010 for the η model, −0.002 ⪕ θ M ⪕ 0.020 for the LR model,
Data taken during 1990.
Data taken during 1991.
Data taken during 1990.
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.
The process e^+e^- -> Z gamma gamma -> q q~ gamma gamma is studied in 0.5 fb-1 of data collected with the L3 detector at centre-of-mass energies between 130.1 GeV and 201.7 GeV. Cross sections are measured and found to be consistent with the Standard Model expectations. The study of the least energetic photon constrains the quartic gauge boson couplings to -0.008 GeV-2 < a_0/\Lambda^2 < 0.005 GeV-2 and -0.007 GeV-2 < a_c/\Lambda^2 < 0.011 GeV-2, at 95% confidence level.
No description provided.
The results are presented for more more restrictive phase space.
CONST(NAME=LAMBDA_NEW) is New Physics scale. COUPLING(NAME=A0,AC) are quartic gauge boson couplings of the effective Lagrangians (see paper for details).
New measurements at a centre-of-mass energy s ≃183 GeV of the hadronic photon structure function F γ 2 ( x ) in the Q 2 interval, 9 GeV 2 ≤ Q 2 ≤30 GeV 2 , are presented. The data, collected in 1997 with the L3 detector, correspond to an integrated luminosity of 51.9 pb −1 . Combining with the data taken at a centre-of-mass energy of 91 GeV, the evolution of F γ 2 with Q 2 is measured in the Q 2 range from 1.2 GeV 2 to 30 GeV 2 . F γ 2 shows a linear growth with ln Q 2 ; the value of the slope α −1 d F γ 2 ( Q 2 )/dln Q 2 is measured in two x bins from 0.01 to 0.2 and is somewhat higher than predicted.
Measured values of F2/ALPHA as a function of x. The second systematic error (DSYS) is that due to the model dependence and is the difference between the results obtained with PHOJET and TWOGAM. The full systematic error is the quadrature sum of the two systematic errors.
A study of neutral-current four-fermion processes is performed using a data sample corresponding to 55.3 pb −1 of integrated luminosity collected by the L3 detector at LEP at an average centre-of-mass energy of 183 GeV. The neutral-current four-fermion cross sections for final states with a pair of charged leptons plus jets and with four charged leptons are measured to be consistent with the Standard Model predictions. Events with fermion pair masses close to the Z boson mass are selected in all observable final states and the ZZ production cross section is measured to be σ ZZ =0.30 +0.22 +0.07 −0.16 −0.03 pb, in agreement with the Standard Model expectation. No evidence for the existence of anomalous triple gauge boson ZZZ and ZZ γ couplings is found and limits on these couplings are set.
No description provided.
The three different helicity states of W bosons, produced in the reaction e+e- -> W+W- -> l nu q q~ are studied using leptonic and hadronic W decays at sqrt{s}=183GeV and 189GeV. The W polarisation is also measured as a function of the scattering angle between the W- and the direction of the e- beam. The analysis demonstrates that W bosons are produced with all three helicities, the longitudinal and the two transverse states. Combining the results from the two center-of-mass energies and with leptonic and hadronic W decays, the fraction of longitudinally polarised W bosons is measured to be 0.261 +/- 0.051(stat.) +/- 0.016(syst.) in agreement with the expectation from the Standard Model.
Fraction of longitudinally polarized W bosons. Combined results from 183 and 189 GeV.