Hadronic and leptonic cross-sections and forward-backward asymmetries are measured using 5.7 pb −1 of data taken with the ALEPH detector at LEP at centre-of-mass energies of 130 and 136 GeV. The results agree with Standard Model expectations. The measurement of hadronic cross-sections far away from the Z resonance improves the determination of the interference between photon and Z exchange. Constraints on models with extra Z bosons are presented.
Forward-Backward Asymmetry with loose SPRIME cuts.
Forward-Backward Asymmetry with tight SPRIME cuts.
Forward-Backward Asymmetry with loose SPRIME cuts.
The polarization of tau leptons in the reaction e+ e- --> tau+ tau- has been measured using a e+e- collider, TRISTAN, at the center-of-mass energy of 58 GeV. From the kinematical distributions of daughter particles in tau --> e nu nu-bar, mu nu nu-bar, rho nu or pi(K) nu decays, the average polarization of tau- and its forward-backward asymmetry have been evaluated to be 0.012 +- 0.058 and 0.029 +- 0.057, respectively.
Charged-conjugated states are included. The forward-backward asymmetry of the polarization is defined as (SIG(F)*POL-SIG(B)*POL)/(SIG(F)*POL+SIG(B)*POL). The last value is the combination of the results for all decay modes. The systematic error is not given.
The polarisation of $\tau$'s produced in Z decay is measured using 160 pb$^{-1}$ of data accumulated at LEP by the ALEPH detector between 1990 and 1995. The variation of the polarisation with polar angle yields the two parameters ${\cal A}_e = 0.1504 \pm 0.0068 $ and ${\cal A}_{\tau} = 0.1451 \pm 0.0059$ which are consistent with the hypothesis of $e$-$\tau$ universality. Assuming universality, the value ${\cal A}_{e{-}\tau} = 0.1474 \pm 0.0045$ is obtained from which the effective weak mixing angle $\sin^2 {\theta_{\mathrm{W}}^{\mathrm{eff}}} =0.23147 \pm 0.00057 $ is derived.
No description provided.
Asymmetries. Systematic error is 1 pct.
Asymmetries. Systematic error is 1 pct.
The search for an additional heavy gauge boson Z′ is described. The models considered are based on either a superstring-motivated E 6 or on a left-right symmetry and assume a minimal Higgs sector. Cross sections and asymmetries measured with the L3 detector in the vicinity of the Z resonance during the 1990 and 1991 running periods are used to determine limits on the Z-Z′ gauge boson mixing angle and on the Z′ mass. For Z′ masses above the direct limits, we obtain the following allowed ranges of the mixing angle, θ M at the 95% confidence level: −0.004 ⪕ θ M ⪕ 0.015 for the χ model, −0.003 ⪕ θ M ⪕ 0.020 for the ψ model, −0.029 ⪕ θ M ⪕ 0.010 for the η model, −0.002 ⪕ θ M ⪕ 0.020 for the LR model,
Data taken during 1990.
Data taken during 1991.
No description provided.
No description provided.
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.
Measurements of the tau lepton polarization and forward-backward polarization asymmetry near the Z resonance using the OPAL detector are described. The measurements are based on analyses of tau -> e nu_e nu_tau, tau -> mu nu_mu nu_tau, tau -> pi nu_tau, tau -> rho nu_tau and tau -> a1 nu_tau decays from a sample of 144810 e+e- -> tau+ tau- candidates corresponding to an integrated luminosity of 151 pb-1. Assuming that the tau lepton decays according to V-A theory, we measure the average tau polarization near Ecm = MZ to be <Ptau> = (-14.10 +/- 0.73 +/- 0.55)% and the tau polarization forward-backward asymmetry to be Afb = (-10.55 +/- 0.76 +/- 0.25)%, where the first error is statistical and the second systematic. Taking into account the small effects of the photon propagator, photon-Z interference and photonic radiative corrections, these results can be expressed in terms of the lepton neutral current asymmetry parameters: Atau = 0.1456 +/- 0.0076 +/- 0.0057, Ae = 0.1454 +/- 0.0108 +/- 0.0036. These measurements are consistent with the hypothesis of lepton universality and combine to give Al = 0.1455 +/- 0.0073. Within the context of the Standard Model this combined result corresponds to sin^2(theta)(lept,effective) = 0.23172 +/- 0.00092. Combing these results with those from the other OPAL neutral current measurements yields a value of sin^2(theta)(lept,effective) = 0.23211 +/- 0.00068.
No description provided.
We present final measurements of the Z boson-lepton coupling asymmetry parameters Ae, Amu, and Atau with the complete sample of polarized Z bosons collected by the SLD detector at the SLAC Linear Collider. From the left-right production and decay polar angle asymmetries in leptonic Z decays we measure Ae = 0.1544 +- 0.0060, Amu = 0.142 +- 0.015, and Atau = 0.136 +- 0.015. Combined with our left-right asymmetry measured from hadronic decays, we find Ae = 0.1516 +- 0.0021. Assuming lepton universality, we obtain a combined effective weak mixing angle of sin**2 theta^{eff}_W = 0.23098 +- 0.00026.
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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