By combining results from the MARK-J at PETRA on Bhabha scattering, μ + μ - and τ + τ - production with recent world data from neutrino-electron scattering experiments, we determine unique values for the leptonic weak neutral current coupling constants g V and g A in the framework of electroweak models containing a single Z 0 . In contrast to previous analyses, we only use data from purely leptonic interactions, and therefore avoid the inherent uncertainties resulting from the use of hadronic targets. From the MARK-J data alone in the context of the standard SU(2) ⊗ U (1) model of Glashow, Weinberg and Salam, we find sin 2 θ W =0.24±0.11.
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We have performed a high-statistics measurement of Bhabha scattering and of the production of hadrons in electron-positron annihilation at PETRA energies (12 GeV<~s<~36.7 GeV). Combining the results with measurements of μ+μ− and τ+τ− production enables us to compare our results with electroweak theory. We find sin2θw=0.27±0.08. This is in good agreement with the value obtained from neutrino experiments which were carried out in entirely different kinematic regions.
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ASYMMETRY WAS USED.
We report on the measurement of the reaction e+e−→e+e− with a large—solid-angle electromagnetic shower detector at center-of-mass energies s=13 and 17 GeV. Comparison of our results with predictions of quantum electrodynamics shows excellent agreement in both the angular distribution and energy dependence. Values of cutoff parameters are also given.
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Measurements of the reactions e++e−→e++e−, μ++μ−, and τ++τ− at PETRA energies (s12=13,17,27.4,30 and 31.6 GeV) are reported. The results show that these reactions agree well with the predictions of quantum electrodynamics thus determining that all the known charged leptons are pointlike particles to a distance < × 10−16 cm.
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Differential cross sections fore+e−→e+e−, τ+, τ- measured with the CELLO detector at\(\left\langle {\sqrt s } \right\rangle= 34.2GeV\) have been analyzed for electroweak contributions. Vector and axial vector coupling constants were obtained in a simultaneous fit to the three differential cross sections assuming a universal weak interaction for the charged leptons. The results,v2=−0.12±0.33 anda2=1.22±0.47, are in good agreement with predictions from the standardSU(2)×U(1) model for\(\sin ^2 \theta _w= 0.228\). Combining this result with neutrino-electron scattering data gives a unique axial vector dominated solution for the leptonic weak couplings. Assuming the validity of the standard model, a value of\(\sin ^2 \theta _w= 0.21_{ - 0.09}^{ + 0.14}\) is obtained for the electroweak mixing angle. Additional vector currents are not observed (C<0.031 is obtained at the 95% C.L.).
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Combined MU and TAU asymmetry. See PL 114B(1982)282 (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+1234> RED = 1234 </a>) and ZP C14(1982)283 (<a href=http://durpdg.dur.ac.uk/scripts/reacsearch.csh/TESTREAC/red+1245> RED = 1245 </a>) for individual asymmetry measurements.
We have searched for resonances in the reaction e+e−→hadrons, γγ, μμ, and ee, in the energy range 39.79<s<45.52 GeV, using the Mark J detector at PETRA. We obtain stringent upper limits on the production of toponium and particles postulated to explain Z0→leptonpair+γ events observed at the CERN p―p collider. We also set limits on the mass and coupling constant of excited electrons.
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DATA ARE CORRECTED FOR TWO-PHOTON AND TAU PRODUCTION EFFECTS, ACCEPTANCE AND QED RADIATIVE EFFECTS UP TO ORDER ALPHA**3. THERE IS ALSO A 6 PCT NORMALISATION ERROR NOT INCLUDED. THE OVERALL AVERAGE VALUE OF R FROM THIS DATA IS 3.88 +- 0.04 +- 0.22.
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SEE PRL 55, 665 FOR MOST RECENT VALUES OF THE MU+ MU- CROSS SECTIONS.
We present an analysis of electroweak leptonic couplings from high statistics experiments on Bhabha scattering and μ pair production at an energy of 34.5 GeV. The forward-backward charge asymmetry of the μ pairs was measured to be −0.098±0.023±0.005. The data were found to agree well with the standard theory of electroweak interaction giving sin2θW=0.27±0.07. The leptonic weak couplings were determined to begv=0.000±0.170 andgA=−0.481±0.055. The data were also used to investigate a class of composite models for leptons.
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Based on 520 000 fermion pairs accumulated during the first three years of data collection by the ALEPH detector at LEP, updated values of the resonance parameters of theZ are determined to beMZ=(91.187±0.009) GeV, ΓZ=(2.501±0.012) GeV, σhad0=(41.60±0.27) nb, andRℓ=20.78±0.13. The corresponding number of light neutrino species isNν=2.97±0.05. The forward-backward asymmetry in lepton-pair decays is used to determine the ratio of vector to axial-vector couplings of leptons:gV2(MZ2)/gA2(MZ2)=0.0052±0.0016. Combining this with ALEPH measurements of theb andc quark asymmetries and τ polarization gives sin2θWeff=0.2326±0.0013. Assuming the minimal Standard Model, and including measurements ofMW/MZ fromp\(\bar p\) colliders and neutrino-nucleon scattering, the mass of the top quark is\(M_{top} = 156 \pm \begin{array}{*{20}c} {22} \\ {25} \\ \end{array} \pm \begin{array}{*{20}c} {17} \\ {22Higgs} \\ \end{array} \) GeV.
Data from 1990 running period.
Data from 1990 running period.
Data from 1990 running period.
We report on a study of radiative Bhabha and quasi-real Compton scattering at centre-of-mass energies between 50 GeV and 170 GeV, and 20 GeV and 140 GeV, respectively, using the L3 detector at LEP. The analysis is based on data corresponding to an integrated luminosity of 232.2 pb −1 . A total of 2856 radiative Bhabha and 4641 Compton scattering events are collected. Total and differential cross sections for both reactions are presented and found to be in good agreement with QED expectations. Our measurement of Compton scattering at the highest energies obtained so far is used to derive exclusion limits on the coupling λ for the on-shell production of an excited electron e ★ decaying into a γ e pair in the mass range 20 GeV
Measured cross sections for radiative Bhabha scattering events.
Measured cross sections for the quasi-real Compton scattering events.