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The e + e − → τ + τ − process has been measured using the CELLO detector at a mean total centre of mass energy of 34.2 GeV using essentially all the decay channels of the τ lepton. The measured cross section yields R τ =1.03±0.05 (stat)±0.07 (syst). Topological branching fraction are given for τ → 1, 3 or 5 charged tracks. The angular distribution shows a clear 1 + cos 2 θ dependance with a forward-backward asymmetry of -0.103 ± 0.052 corresponding to an axial-vector coupling a τ of the τ to the weak neutral current given by a τ =−1.12 ± 0.57.
Forward-backward asymmetry based on 1 + (cos(theta))**2 + bcos(theta) fit for angular distribution.
The measurement of the nonelectromagnetic forward-backward charge asymmetry in the reaction e+e−→μ+μ− at s∼34.6 GeV and in the angular region 0<|cosθ|<0.8 is reported. With a systematic error less than 1%, we observe an asymmetry of (-8.1±2.1)%. This is in agreement with the standard electroweak theory prediction of (-7.6±0.6)%. The weak-current coupling constants are also reported.
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The reaction (e+e−→μ+μ−) has been measured between\(\sqrt S= 14.0\) and\(\sqrt S= 36.4\). The total cross section result is in good agreement with the QED prediction and the following Λ values have been obtained:Λ+=186 GeV,Λ−=101 GeV. The angular distribution at high energy (\(\left( {\left. {\left\langle {\sqrt S } \right.} \right\rangle= 34.2 GeV} \right)\)) shows a fitted charge asymmetry of −0.064±0.064 in agreement with theW-S model prediction of −0.092, corresponding to an axial coupling parametera2=4ga2=0.69±0.69.
Errors include contribution from systematics. Result based on fit(1 + cos(theta)**2 + q cos(theta)) to corrected angular distribution.
We have measured, at an average centre-of-mass energy of 34.22 GeV a forward-backward charge asymmetry in the reaction e + e − → μ + μ − of value −0.161 ± 0.032. This demonstrates the existence of an axial vector neutral current with coupling strength of g e a g μ a =0.53 ± 0.10. We have also obtained a limit on the vector coupling strength of g e v g μ v <0.12. The Weinberg angle is found to be sin 2 θ W =0.29 +0.09 −0.11 . From the reaction e + e − → τ + τ − we have found g e a g τ a <0.34, g e v g τ v <0.55.
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).
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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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.
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