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.
We report on total cross section and forward backward charge asymmetry measurements of the reactione+e− → τ+τ− at centre of mass energies of 35.0 GeV and 42.4 GeV using the TASSO detector. Including previous data an analysis in terms of electroweak parameters of the standard model is presented, and lower limits on mass scale parameters of residual contact interactions are given. A combined analysis of electroweak couplings using all our results on leptonic reactionse+e−→l+l− has been performed.
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 couplings of the Z 0 to charged leptons are studied using measurements of the lepton pair cross sections and forward-backward asymmetries at centre of mass energies near to the mass of the Z 0 . The data are consistent with lepton universality. Using a parametrisation of the lepton pair differential cross section which assumes that the Z 0 has only vector and axial couplings to leptons, the charged leptonic partial decay width of the Z 0 is determined to be Г ol+ol− = 83.1±1.9 MeV and the square of the product of the effective axial vector and vector coupling constants of the Z 0 to charged leptons to be a ̌ 2 ol v ̌ 2 ol = 0.0039± 0.0083 , in agreement with the standard model. A parametrisation in the form of the improved Born approximation gives effective leptonic axial vector and vector coupling constants a ̌ 2 ol = 0.998±0.024 and v ̌ 2 ol = 0.0044±0.0083 . In the framework of the standard model, the values of the parameters ϱ z and sin 2 θ w are found to be 0.998±0.024 and 0.233 +0.045 −0.012 respectively. Using the relationship in the minimal standard model between ϱ z and sin 2 θ w , the results sin 2 θ SM w = 0.233 +0.007 −0.006 is obtained. Our previously published measurement of the ratio of the hadronic to the leptonic partial width of the Z 0 is update: R z = 21.72 +0.71 −0.65 .
Forward-backward asymmetry corrected for kinematic cuts. Errors have systematics folded.
Forward-backward asymmetry. Statistical errors only.
Forward-backward asymmetry. Statistical errors only.
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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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.).
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.
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.
During 1993 and 1995 LEP was run at 3 energies near the Z$^0$peak in order to give improved measurements of the mass and width of the resonance. During 1994, LEP o
Cross section and forward-backward asymmetry in the E+ E- channel for the 1993 data. The polar angle is 44 to 136 degrees. Additional systematic error for cross section of 0.46 PCT (efficiencies and backgrounds) and 0.29 PCT (absolute luminosity). Additional systematic error for the asymmetry of 0.0026.
Cross section and forward-backward asymmetry in the E+ E- channel for the 1994 data. The polar angle is 44 to 136 degrees. Additional systematic error for cross section of 0.52 PCT (efficiencies and backgrounds) and 0.14 PCT (absolute luminosity). Additional systematic error for the asymmetry of 0.0021.
Cross section and forward-backward asymmetry in the E+ E- channel for the 1995 data. The polar angle is 44 to 136 degrees. Additional systematic error for cross section of 0.52 PCT (efficiencies and backgrounds) and 0.14 PCT (absolute luminosity). Additional systematic error for the asymmetry of 0.0020.
Asymmetries. Systematic error is 1 pct.
Asymmetries. Systematic error is 1 pct.
From measurements of the cross sections for e + e − → hadrons and the cross sections and forward-backward charge-asymmetries for e e −→ e + e − , μ + μ − and π + π − at several centre-of-mass energies around the Z 0 pole with the DELPHI apparatus, using approximately 150 000 hadronic and leptonic events from 1989 and 1990, one determines the following Z 0 parameters: the mass and total width M Z = 91.177 ± 0.022 GeV, Γ Z = 2.465 ± 0.020 GeV , the hadronic and leptonic partial widths Γ h = 1.726 ± 0.019 GeV, Γ l = 83.4 ± 0.8 MeV, the invisible width Γ inv = 488 ± 17 MeV, the ratio of hadronic over leptonic partial widths R Z = 20.70 ± 0.29 and the Born level hadronic peak cross section σ 0 = 41.84±0.45 nb. A flavour-independent measurement of the leptonic cross section gives very consistent results to those presented above ( Γ l = 83.7 ± 0.8 rmMeV ). From these results the number of light neutrino species is determined to be N v = 2.94 ±0.10. The individual leptonic widths obtained are: Γ e = 82.4±_1.2 MeV, Γ u = 86.9±2.1 MeV and Γ τ = 82.7 ± 2.4 MeV. Assuming universality, the squared vector and axial-vector couplings of the Z 0 to charged leptons are: V ̄ l 2 = 0.0003±0.0010 and A ̄ l 2 = 0.2508±0.0027 . These values correspond to the electroweak parameters: ϱ eff = 1.003 ± 0.011 and sin 2 θ W eff = 0.241 ± 0.009. Within the Minimal Standard Model (MSM), the results can be expressed in terms of a single parameter: sin 2 θ W M ̄ S = 0.2338 ± 0.0027 . All these values are in good agreement with the predictions of the MSM. Fits yield 43< m top < 215 GeV at the 95% level. Finally, the measured values of Γ Z and Γ inv are used to derived lower mass bounds for possible new particles.
Forward-backward asymmetry within the polar angular range 44 < THETA < 136 degrees and acollinearity < 10 degrees.. Overall systematic error is 0.005 not included.
Forward-backward asymmetry after t-channel subtraction but in the polar angular range 44 < THETA < 136 degrees and acollinearity < 10 degrees.. Overall systematic error is 0.005 not included.
Forward-backward asymmetry calculated using the counting method. Data are corrected for full solid angle, but not for cuts on momenta or acollinearity.. Additional systematic error is 0.005.
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