The processes e + e − → e + e − and μ + μ − have been studied at PETRA using the JADE detector. The data, which were collected at s -values of up to 1300 GeV 2 have been analysed in terms of an electro-weak extension of QED to obtain values for the weak vector and axial vector couplings in the lepton sector. The values obtained agree with the predictions of the standard Salam-Weinberg model and the data are further analysed in terms of this model to obtain the limits 0.10 < sin 2 ϑ w < 0.40 (68% CL). The mass of the neutral weak gauge boson is deduced to be greater than 51 GeV/ c 2 .
No description provided.
The angular distribution and the s dependence of the total cross section for the process e + e − → μ + μ − have been measured using the JADE detector at PETRA. After radiative corrections, a forward-backward asymmetry of −(11.8±3.8) % was observed at an average centre of mass energy of 33.5 GeV. For comparison, an asymmetry of −7.8 % is expected on the basis of the standard Glashow-Salam-Weinberg model.
Forward-backward asymmetry within the acceptnce region.
Forward-backward asymmetry from fit to angular distribution for the form 1 + cos(theta)**2 + Bcos(theta).
The production of collinear muon pairs has been studied using the JADE detector at thee+e− storage ring at PETRA. Results for the total cross section and the angular distribution were obtained at centre of mass (cm) energies ranging from 12 to 46 GeV. The data correspond to an integrated luminosity offLdt>90 pb−1, of which 71.2 pb−1 were taken at\(\left\langle {\sqrt s } \right\rangle \)=34.4 GeV and 17 pb−1 at\(\left\langle {\sqrt s } \right\rangle \)=42.4 GeV. The results are compared to electroweak theories, in particular the “Standard Model”.
Forward-backward asymmetry calculated from a fit to the angular distribution of the form 1: + cos(theta)**2 + Bcos(theta).. Asymmetries quoted here are extrapolated to full solid angle. The asymmetry at sqrt(s) = 34.4 is -11.10 +- 1.75 +- 1.0 pct if the end-cap points are included.
No description provided.
An analysis of the three leptonic reactionse+e−→e+e−,μ+μ− andτ+τ− over a wide range of energy,\(12< \sqrt s< 46.78 GeV\) is presented. The data were obtained with the JADE detector at thee+e− storage ring PETRA. They are compared to predictions of electroweak theories, in particular the standard model. For the total cross-sections of all three reactions and for the differential cross-section of Bhabha scattering no deviation from QED is found over the entire energy range. The differential cross-sections of μ and τ pairs at high energies show the angular asymmetry predicted by electroweak interference. The axial-vector and vector weak coupling constant, sin2θW andMZ are determined and compared to other measurements. Finally, limits on deviations from the standard model are given.
Forward-Backward Asymmetry measurements.
Forward-Backward Asymmetry measurements.
No description provided.
The reactions e + e − → μ + μ − and τ + τ − were measured at s =52 GeV and 55 GeV by using the TOPAZ detector at TRISTAN. For the combined data, the observed charge asymmetry is −0.29±0.13 and the total cross section is 27.9±3.0 (stat.)±0.8 (syst.) pb for μ + μ − production, and those for τ + τ − production are −0.20±0.14 and 35.7±4.3 (stat.)±2.4 (syst.)pb, respectively. These values are consistent with predictions by the standard model of electroweak interactions.
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The e + e − → μ + μ − reaction has been studied at centre of mass energies ranging between 38.3 abd 46.8 GeV with the CELLO detector at PETRA. We present results on the cross section and the charge asymmetry for this channel. Combining all the data at the average energy 〈 s 〉=43 GeV we obtain R μμ =〈 σ μμ / σ 0 〉=0.98±0.04±0.04, 〈 A μμ 〉=(−14.1±3.7±1.0)%, where σ 0 is the QED cross section and A μμ is the charge asymmetry corrected for pure radiative effects. These results are in good agreement with the expected values of R μμ =1.01 and A μμ =−14.5% at that energy.
Forward-backward asymmetry.
The process e + e − → μ + μ − and e + e − have been studied in the energy range s =52−61.4 GeV , using the TOPAZ detector at TRISTAN. From an integrated luminosity of L = 74.0 pb −1 , lowest-order cross sections and forward-backward asymmetries are measured to be 〈σ μμ 〈 = 25.4±0.9±1.2 pb , 〈A μμ 〉 = (−32.2±3.1±1.1)%, 〈σ ττ 〉 = 27.1±1.1±1.2 pb , 〈A ττ 〉 = (−33.9±4.9±1.0)% , at an average energy of s 〉=57.87 GeV . From the measured assymetry we derive axial vector couplings of a c a μ =0.96±0.09±0.01,and a c a τ =1.01±0.14±0.01±. These results are consistent with standard model expectations. Lower limits in the range 2–5 TeV (95%CL)are placed on compositeness scale parameters for leptons.
No description provided.
The angular distributions of the reactione+e−→μ+μ− ande+e+→τ+τ− have been measured between\(\sqrt s= 50\) and 60.8 GeV with the VENUS detector at TRISTAN. The average total cross section and the forward-backward charge asymmetry for μ-pair production are observed to be 28.3±1.4±0.8 pb and (−29.0−4.8+5.0±0.5)%, and those for τ-pair production are 27.6±1.7±1.0 pb and (−32.8−6.2+6.4±1.5)% at\(\langle \sqrt s \rangle \). These values are consistent with the predictions of the standard model of electroweak interactions.
No description provided.
No description provided.
No description provided.
Differential cross section data of the CELLO experiment on pair production of muons, taus, and heavy quarks ine+e−-annihilation are presented and analysed, together with our data on Bhabha scattering, in terms of compositeness effects characterized by the mass scale Λ. We discuss difficulties in the combination of limits Λ from different experiments. The appropriate parameter to combine different results turns out to be ɛ=±1/Λ2, which is in contrast to Λ Gaussian distributed.
Charge asymmetry for charm quarks derived from the differential cross section data.
Charge asymmetry for bottom quarks derived from the differential cross section data.
The reactione+e−→µ+µ− has been studied at centre of mass energies between 35.0 and 46.8 GeV using the TASSO detector at PETRA. We present measurements of the forward-backward charge asymmetry (Aμμ) and cross section σμμ for this reaction at three energies. At 35.0 GeV we obtain a cross section relative to the QED prediction ofRμμ=σμμ/σo=0.932±0.018±0.044 andAμμ=(−10.6−2.3+2.2±0.5)%. At 38.3 GeV we findRμμ=0.951±0.072−0.057+0.063 andAμμ=(+1.7−8.6+8.5±0.5)%. At 43.6 GeV we measureRμμ=0.921±0.037±0.055 andAμμ=(−17.6−4.3+4.4±0.5)%. Our results are in good agreement with the predictions of the standard model. Including previous TASSO data we present improved determinations of muonic electroweak parameters. We also report on lower limits of possible contributions from contact interactions.
No description provided.
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