A measurement of the cross section for production of collinear muon pairs based upon a sample of about 3000 events observed in the MAC detector at the storage ring PEP is presented. From the angular asymmetry Aμμ=0.076±0.018 the axial-vector weak neutral coupling is found to be given by gAegAμ=0.31±0.08.
Asymmetry measurement based on extrapolation of number of events to 4 PI acceptance.
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Data extrapolated to full solid angle.
A high-statistics measurement has been made of the process e+e−→μ+μ− at s=29 GeV with the MAC detector at the SLAC storage ring PEP. The electroweak forward-backward charge asymmetry for a sample of approximately 16 000 events was measured to be Aμμ=−0.063±0.008±0.002. The ratio of the cross section to the lowest-order QED cross section was measured to be Rμμ=1.01±0.01±0.03. From these results the weak neutral axial-vector and vector couplings are determined to be gAegAμ=0.25±0.03±0.01 and gVegVμ=−0.02±0.03±0.09.
Asymmetry determined from a two parameter fit to the angular distribution proportional to R*(1 + cos(theta)**2 + (8/3)*A*cos(theta)). R is then the total ratio relative to the lowest order QED cross section and A is the forward-backward asymmetry.
No description provided.
A high-statistics measurement is presented of the cross section for the process e+e−→τ+τ− at s=29 GeV from the MAC detector at PEP. A fit to the angular distribution of our sample of 10 153 events with |cosθ|<0.9 gives an asymmetry Aττ=−0.055±0.012±0.005 from which we find the product of electron and tau axial-vector weak neutral couplings gAegAτ=0.22±0.05.
Data extrapolated to full acceptance.
No description provided.
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.
The reaction e + e − → τ + τ − has been studied at centre of mass energies between 14.0 and 46.8 GeV with the CELLO detector at the PETRA e + e − collider. We present results for the cross section σ τ and the charge asymmetry A τ . The results are in good agreement with the standard model. We have also measured the topological decay rates BR 1 , BR 3 and BR 5 for the inclusive decay of the τ lepton into one, three and five charge particles. The results confirm and improve earlier CELLO measurements at other energies. We find for the combined values at all energies BR 1 = (84.9 ± 0.4 ± 0.3)%, BR 3 = (15.0 ± 0.4 ± 0.3)% and BR 5 = (0.16 ± 0.13 ± 0.04)%.
Corrected for radiative effects and background contributions.
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 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.
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.
Cross-section and angular distributions for hadronic and lepton-pair final states in e+e- collisions at centre-of-mass energies between 189 GeV and 209 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The measurements are used to determine the electromagnetic coupling constant alphaem at LEP2 energies. In addition, the results are used together with OPAL measurements at 91-183 GeV within the S-matrix formalism to determine the gamma-Z interference term and to make an almost model-independent measurement of the Z mass. Limits on extensions to the Standard Model described by effective four-fermion contact interactions or the addition of a heavy Z boson are also presented.
Measured forward backward asymmetries for MU+ MU- production. The data are corrected to no interference between initial and final state radiation.
Measured forward backward asymmetries for TAU+ TAU- production. The data are corrected to no interference between initial and final state radiation.
Measured forward backward asymmetries for E+ E- production.
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