During the LEP running periods in 1990 and 1991 DELPHI has accumulated approximately 450 000 Z 0 decays into hadrons and charged leptons. The increased event statistics coupled with improved analysis techniques and improved knowledge of the LEP beam energies permit significantly better measurements of the mass and width of the Z 0 resonance. Model independent fits to the cross sections and leptonic forward- backward asymmetries yield the following Z 0 parameters: the mass and total width M Z = 91.187 ± 0.009 GeV, Γ Z = 2.486 ± 0.012 GeV, the hadronicf and leptonic partials widths Γ had = 1.725 ± 0.012 GeV, Γ ℓ = 83.01 ± 0.52 MeV, the invisible width Γ inv = 512 ± 10 MeV, the ratio of hadronic to leptonic partial widths R ℓ = 20.78 ± 0.15, and the Born level hadronic peak cross section σ 0 = 40.90 ± 0.28 nb. Using these results and the value of α s determined from DELPHI data, the number of light neutrino species is determined to be 3.08 ± 0.05. The individual leptonic widths are found to be: Γ e = 82.93 ± 0.70 MeV, Γ μ = 83.20 ± 1.11 MeV and Γ τ = 82.89 ± 1.31 MeV. Using the measured leptonic forward-backward asymmetries and assuming lepton universality, the squared vector and axial-vector couplings of the Z 0 to charged leptons are found to be g V ℓ 2 = (1.47 ± 0.51) × 10 −3 and g A ℓ 2 = 0.2483 ± 0.0016. A full Standard Model fit to the data yields a value of the top mass m t = 115 −82 +52 (expt.) −24 +52 (Higgs) GeV, corresponding to a value of the weak mixing angle sin 2 θ eff lept = 0.2339±0.0015 (expt.) −0.0004 +0.0001 (Higgs). Values are obtained for the variables S and T , or ϵ 1 and ϵ 3 which parameterize electroweak loop effects.
E+ E- forward-backward asymmetries from the 1990 data set for both final state fermions in the polar angle range 44 to 136 degrees and accollinearity < 10 degrees (the s + t data).
E+ E- forward-backward asymmetries from the 1991 data set for both final state fermions in the polar angle range 44 to 136 degrees and accollinearity < 10 degrees (the s + t data). Additional systematic error, excluding luminosity, is 0.002.
E+ E- forward-backward asymmetries from the 1990 data set after t-channel subtraction with only the E- constraint by polar angle 44 to 136 degrees and accollinearity < 10 degrees. Additional systematic error, excluding luminosity, is 0.003 at the peak.
From the measured ratio of the invisible and the leptonic decay widths of theZ0, we determine the number of light neutrino species to beNv=3.05±0.10. We include our measurements of the forward-backward asymmetry for the leptonic channels in a fit to determine the vector and axial-vector neutral current coupling constants of charged leptons to theZ0. We obtain\(\bar g_V=- 0.046_{ - 0.012}^{ + 0.015}\) and\(\bar g_A=- 0.500 \pm 0.003\). In the framework of the Standard Model, we estimate the top quark mass to bemt=193−69+52±16 (Higgs) GeV, and we derive a value for the weak mixing angle of sin2θW=1−(MW/MZ)2=0.222 ± 0.008, corresponding to an effective weak mixing angle of\(\sin ^2 \bar \theta _W= 0.2315\pm0.0025\).
Asymmetry determined from the number of events in the forward and backward hemisphere. Estimated systematic error is 0.005.
Asymmetry determined using the maximum likelihood method. Estimated systematic error is 0.005.
Asymmetry determined from the number of events in the forward and backward hemisphere. Estimated systematic error is <0.01.
The properties of theZ resonance are measured on the basis of 190 000Z decays into fermion pairs collected with the ALEPH detector at LEP. Assuming lepton universality,Mz=(91.182±0.009exp±0.020L∶P) GeV,ГZ=(2484±17) MeV, σhad0=(41.44±0.36) nb, andГjad/Гℓℓ=21.00±0.20. The corresponding number of light neutrino species is 2.97±0.07. The forward-back-ward asymmetry in leptonic decays is used to determine the ratio of vector to axial-vector coupling constants of leptons:gv2(MZ2)/gA2(MZ2)=0.0072±0.0027. Combining these results with ALEPH results on quark charge and\(b\bar b\) asymmetries, and τ polarization, sin2θW(MZ2). In the contex of the Minimal Standard Model, limits are placed on the top-quark mass.
No description provided.
No description provided.
No description provided.
Drell-Yan lepton pairs are produced in the process $p\bar{p} \rightarrow \mu^+\mu^- + X$ through an intermediate $\gamma^*/Z$ boson. The forward-backward asymmetry in the polar-angle distribution of the $\mu^-$ as a function of the invariant mass of the $\mu^+\mu^-$ pair is used to obtain the effective leptonic determination $\sin^2 \theta^{lept}_{eff}$ of the electroweak-mixing parameter $\sin^2 \theta_W$, from which the value of $\sin^2 \theta_W$ is derived assuming the standard model. The measurement sample, recorded by the Collider Detector at Fermilab (CDF), corresponds to 9.2 fb-1 of integrated luminosity from $p\bar{p}$ collisions at a center-of-momentum energy of 1.96 TeV, and is the full CDF Run II data set. The value of $\sin^2 \theta^{lept}_{eff}$ is found to be 0.2315 +- 0.0010, where statistical and systematic uncertainties are combined in quadrature. When interpreted within the context of the standard model using the on-shell renormalization scheme, where $\sin^2 \theta_W = 1 - M_W^2/M_Z^2$, the measurement yields $\sin^2 \theta_W$ = 0.2233 +- 0.0009, or equivalently a W-boson mass of 80.365 +- 0.047 GeV/c^2. The value of the W-boson mass is in agreement with previous determinations in electron-positron collisions and at the Tevatron collider.
The fully corrected measurement of ASYM(FB) as a function of the muon-pair invariant mass.
A significant charge asymmetry is observed in the hadronic Z decays with the ALEPH detector at LEP. The asymmetry expressed in terms of the difference in momentum weighted charges in the two event hemispheres is measured to be < Q forward >−< Q backward >= −0.0084±0.0015 (stat.) ±0.0004 (exp. sys.). In the framework of the standard model this can be interpreted as a measurement of the effective electroweak mixing angle, sin 2 O w ( M z 2 =0.2300±0.0034 (stat.) ±0.0010 (exp. sys.) ±0.0038 (theor. sys.) or of the ratio of the vector to axual- vector coupling costants of the electron, g ve g Ae =+0.073±0.024.
No description provided.
A precise measurement of the strange quark forward-backward asymmetry used 3.2M multihadronic events around the Z$^0$peak collected by the DELPHI experiment from 1
No description provided.
Based on 520 000 fermion pairs accumulated during the first three years of data collection by the ALEPH detector at LEP, updated values of the resonance parameters of theZ are determined to beMZ=(91.187±0.009) GeV, ΓZ=(2.501±0.012) GeV, σhad0=(41.60±0.27) nb, andRℓ=20.78±0.13. The corresponding number of light neutrino species isNν=2.97±0.05. The forward-backward asymmetry in lepton-pair decays is used to determine the ratio of vector to axial-vector couplings of leptons:gV2(MZ2)/gA2(MZ2)=0.0052±0.0016. Combining this with ALEPH measurements of theb andc quark asymmetries and τ polarization gives sin2θWeff=0.2326±0.0013. Assuming the minimal Standard Model, and including measurements ofMW/MZ fromp\(\bar p\) colliders and neutrino-nucleon scattering, the mass of the top quark is\(M_{top} = 156 \pm \begin{array}{*{20}c} {22} \\ {25} \\ \end{array} \pm \begin{array}{*{20}c} {17} \\ {22Higgs} \\ \end{array} \) GeV.
Data for 1991 running period.
Data for 1991 running period.
Data for 1991 running period.
We present a new measurement of the left-right cross section asymmetry (ALR) for Z boson production by e+e- collisions. The measurement was performed at a center-of-mass energy of 91.28 GeV with the SLD detector at the SLAC Linear Collider (SLC). The luminosity-weighted average polarization of the SLC electron beam was (77.23+-0.52)%. Using a sample of 93,644 Z decays, we measure the pole-value of the asymmetry, ALR0, to be 0.1512+-0.0042(stat.)+-0.0011(syst.) which is equivalent to an effective weak mixing angle of sin**2(theta_eff)=0.23100+-0.00054(stat.)+-0.00014(syst.).
No description provided.
The left-right asymmetry and effective weak mixing angle corrected to the pole energy value, taking into account photon exclusive and electroweak interference effects of total-state radiation.
During the 1992 running period of the LEP e + e − collider, the DELPHI experiment accumulated approximately 24 pb − of data at the Z 0 peak. The decays into hadrons and charged leptons have been analysed to give values for the cross sections and leptonic forward-backward asymmetries which are significantly improved with respect to those previously published by the DELPHI collaboration. Incorporating these new data, more precise values for the Z 0 resonance parameters are obtained from model-independent fits. The results are interpreted within the framework of the Standard Model, yielding for the top quark mass m t = 157 −48 +36 (expt.) −20 +19 (Higgs) GeV, and for the effective mixing angle sin 2 θ eff lept = 0.2328 ± 0.0013 (expt.) −0.0003 +0.0001 (Higgs), where (Higgs) represents the variation due to Higgs boson mass in the range 60 to 1000 GeV, with central value 300 GeV.
Forward-backward asymmetry within the polar angular range 44 < THETA < 136 degrees and acollinearity < 10 degrees.. First result corresponds to the total cross section (i.e. S+T channel), while second one corresponds to S-channel only.
No description provided.
No description provided.
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.
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