We report on a measurement of the mass of the Z 0 boson, its total width, and its partial decay widths into hadrons and leptons. On the basis of 25 801 hadronic decays and 1999 decays into electrons, muons or taus, selected over eleven energy points between 88.28 GeV and 95.04 GeV, we obtain from a combined fit to hadrons and leptons a mass of M z =91.154±0.021 (exp)±0.030 (LEP) GeV, and a total width of Γ z =2.536±0.045 GeV. The errors on M z have been separated into the experimental error and the uncertainty due to the LEP beam energy. The measured leptonic partial widths are Γ ee =81.2±2.6 MeV, Γ μμ =82.6± 5.8 MeV, and Γ ττ =85.7±7.1 MeV, consistent with lepton universality. From a fit assuming lepton universality we obtain Γ ℓ + ℓ − = 81.9±2.0 MeV. The hadronic partial width is Γ had =1838±46 MeV. From the measured total and partial widths a model independent value for the invisible width is calculated to be Γ inv =453±44 MeV. The errors quoted include both the statistical and the systematic uncertainties.
Errors are statistical and point to point systematic luminosity error of 1 pct.
Measured values of e+ e- --> e+ e- cross section.
Corrected cross section. Corrections are for t-channel effects and loss of acollinear events near the boundary of the acceptance.
A measurement of the cross section for e + e - → hadrons using 11 000 hadronic decays of the Z boson at ten different center-of-mass energies is presented. A three-parameter fit gives the following values for the Z mass M z , the total width Γ z , the product of the electronic and hadronic partial widths Γ e Γ h , and the unfolded pole cross section σ 0 : M Z =91.171±0.030(stat)±0.030 (beam) GeV, Γ Z =2.511±0.065 GeV, Γ e Γ h =0.148±0.006 (stat.)±0.004 (syst.) GeV 2 , σ 0 =41.6±0.7(stat.)±1.1 (syst.) nb,
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The production of strange baryons ine+e− annihilation has been studied at centre of mass energies of 34.8 GeV and 42.1 GeV, using the TASSO detector at DESY. Inclusive cross-sections have been obtained forΛ0 andΞ− production and an upper limit has been placed upon the production rate of Σ*±(1385). We measure theΛ0 multiplicity per event to be\(\begin{gathered}\hfill \\0.218_{ - 0.011}^{ + 0.011}\pm 0.021 \hfill \\ \end{gathered} \) and\(0.256_{ - 0.029}^{ + 0.030}\pm 0.025\) at\(\sqrt s=34.8\) and 42.1 GeV respectively. The Ξ− multiplicity per event is found to be\(0.014_{ - 0.003}^{ + 0.003}\pm 0.004\) at\(\sqrt s=34.8 GeV\). An investigation has been made of the extent to whichΛ0 are produced in pairs. TheΛ0 cross-section has been studied as a function of event sphericity.
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We report on a study of inclusive production ofD*± mesons ine+e− annihilation at c.m. energies between 28 and 46.8 GeV using the TASSO detector at the PETRA storage ring. A hardD*± energy spectrum is measured with a maximum nearED*±≃0.6Ebeam. The measured cross section ratio\((\sigma _{D^{* + } }+ \sigma _{D^{* - } } )/\sigma _{\mu \mu }= 1.28 \pm 0.09 \pm 0.18\) indicates thatD* production accounts for a large fraction of the observed charm production. Two complementary methods have been used to determine the forward-backward asymmetry of charm pair production due to electroweak interference. Combining both measurements the product of the axial vector couplings of the electron and the charm quark to the weak neutral current was determined to begAegAc=−(0.276±0.073), in agreement with the standard model prediction of −0.25. Using a sample of reconstructedD*± mesons, the relative strength of the strong interaction coupling of thec quark compared to that of an average of all flavours is measured as αs(c)/αs(all)=0.91±0.38±0.15, consistent with the coupling constant being flavour independent. An update of ourD0 lifetime measurement is presented, based on a considerable increase in statistics, the final result being\(\tau _{D^0= } (4.8 \pm _{0.9 - 0.7}^{1.0 + 0.5} )10^{ - 13} s\).
Cross sections using D0 --> K- PI+ channel.
Cross sections using D0 --> K- PI+ PI- PI+ channel.
No description provided.
Differential cross sections fore+e−→γγ have been measured at center-of-mass energies of 55, 56, 56.5 and 57 GeV. The results are in good agreement with those predicted by QED. Possible deviations from QED are studied in terms of contact interactions, and the limits on compositeness scales are obtained. Using events with a gramma pair in the final state, a search is made for the pair production of unstable photons,\(e^ +e^ -\to \tilde \gamma\tilde \gamma \). No candidate events were found and a new limit on the photino mass is obtained.
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We have measured the total e + e − hadronic annihilation cross section at the center of mass energies between 50.0 GeV and 61.4 GeV with the TOPAZ detector at TRISTAN. The full electroweak radiative corrections (up to O(α 3 )) were applied to the data which were analysed together with the published data from PEP and PETRA. We then determined the standard model parameters, M z (the mass of the Z), sin w 2 θ (the Weinberg angle) and Λ MS (the QCD scale parameter) by comparing the experimental data with the prediction of the standard model. The best fit values are M z = 89.2 −1.8 +2.1 GeV/c 2 , sin 2 θ w = 0.233 −0.025 +0.035 and Λ MS = 0.327 −0.206 +0.275 GeV. A constraint is obtained on the heavy top quark mass through the radiative corrections if we take the SLC value of M z (91.1 GeV / c 2 ).
No description provided.
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We have made a precise measurement of the cross section for e + e − →Z 0 →hadrons with the L3 detector at LEP, covering the s range from 88.28 to 95.04 GeV. From a fit to the Z 0 mass, total width, and the hadronic cross section to be M Z 0 =91.160 ± 0.024 (experiment) ±0.030(LEP) GeV, Γ Z 0 =2.539±0.054 GeV, and σ h ( M Z 0 )=29.5±0.7 nb. We also used the fit to the Z 0 peak cross section and the width todetermine Γ invisible =0.548±0.029 GeV, which corresponds to 3.29±0.17 species of light neutrinos. The possibility of four or more neutrino flavors is thus ruled out at the 4σ confidence level.
No description provided.
Total hadronic cross section.
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.
The full TASSO data have been used to study the inclusive production of strange mesons ine+e− annihilations. Differential and total cross sections have been measured in the centre of mass energy range 14 to 44 GeV forK0,\(\bar K^0\) and 34.5 to 44 GeV forK*± (892). We have investigated the strange meson production properties in jets by studying the rapidity andpt2 distributions as well as the evolution of the multiplicities as a function of the event sphericity. We find no evidence that the strange meson yields increase with increasing sphericity faster than the total charged multiplicity.
Scaled differential cross sections for K0 production. Errors are statistical and systematic combined.
Scaled differential cross section for K0 production. Errors are statistical and systematic combined.
Scaled differential cross section for K0 production. Errors are statistical and systematic combined.
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