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.
A measurement of the charm and bottom forward-backward asymmetry in e+e− annihilations is presented at energies on and around the peak of the Z0 resonance. Decays of the Z0 into charm and bottom quarks are tagged using D mesons identified in about 4 million hadronic decays of the Z0 boson recorded with the OPAL detector at LEP between 1990 and 1995. Approximately 33000 D mesons are tagged in seven different decay modes. From these the charm and bottom asymmetries are measured in three energy ranges around the Z0 peak: \(\matrix {A_{\rm FB}^{\rm c}=0.039\pm 0.051\pm 0.009\cr A_{\rm FB}^{\rm c}=0.063\pm 0.012\pm 0.006\cr A_{\rm FB}^{\rm c}=0.158\pm 0.041\pm 0.011}\)\(\matrix {A_{\rm FB}^{\rm b}=0.086\pm 0.108\pm 0.029\cr A_{\rm FB}^{\rm b}=0.094\pm 0.027\pm 0.022\cr A_{\rm FB}^{\rm b}=0.021\pm 0.090\pm 0.026}\)\(\matrix{\langle E_{cm}\rangle =89.45\ {\rm GeV}\cr \langle E_{cm}\rangle =91.22\ {\rm GeV}\cr \langle E_{cm}\rangle =93.00\ {\rm GeV}}\) The results are in agreement with the predictions of the standard model and other measurements at LEP.
Forward-backward asymmetry.
No description provided.
We present the first 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 91.55 GeV with the SLD detector at the SLAC Linear Collider which utilized a longitudinally polarized electron beam. The average beam polarization was (22.4±0.6)%. Using a sample of 10 224 Z decays, we measure ALR to be 0.100±0.044(stat)±0.004(syst), which determines the effective weak mixing angle to be sin2θWeff=0.2378 ±0.0056(stat)±0.0005(syst).
R and L refer to Right and Left handed beam polarization.
Effective weak mixing angle.
We present a measurement of the forward-backward charge asymmetry in hadronic decays of the Z 0 using data collected with the OPAL detector at LEP. The forward-backward charge asymmetry was measured using a weight function method which gave the number of forward events on a statistical basis. In a data sample of 448 942 hadronic Z 0 decays, we have observed a charge asymmetry of A h = 0.040±0.004 (stat.)±0.006 (syst.)±0.002 (B 0 B 0 mix.), taking into account the effect of B 0 B 0 mixing. In the framework of the standard model, this asymmetry corresponds to an effective weak mixing angle averaged over five quark flavours of sin 2 θ W = 0.2321 ± 0.0017 ( stat. ) ± 0.0027 ( syst. ) ± 0.0009 (B 0 B 0 mix.). The result agrees with the value obtained from the Z 0 line shape and lepton pair forward-backward asymmetry.
No description provided.
The second systematic error is due to the uncertainty in the correction for B.BBAR mixing which had been applied to the data.
The second systematic error is due to the uncertainty in the correction for B.BBAR mixing which had been applied to the data.
An analysis of the forward-backward asymmetry in Z0 decays using data from the Collider Detector at Fermilab at √s =1.8 TeV yields AFB=[5.2±5.9(stat)±0.4(syst)]% and sin2θ¯W =0.228−0.015+0.017(stat)±0.002(syst).
Asymmetry after background and QCD corrections.
SIN2TW derived from asymmetry measurement fully corrected for background and radiative corrections.
We have determined mW=79.91±0.39 GeV/c2 from an analysis of W→eν and W→μν data from the Collider Detector at Fermilab in p¯p collisions at a c.m. energy of √s =1.8 TeV. This result, together with the world-average Z mass, determines the weak mixing angle to be sin2θW=0.232±0.008. Bounds on the top-quark mass are discussed.
Combining W mass result with world-average Z mass (91.191 GEV).
We report on high statistics Bhabha scattering data taken with the TASSO experiment at PETRA at center of mass energies from 12 GeV to 46.8 GeV. We present an analysis in terms of electroweak parameters of the standard model, give limits on QED cut-off parameters and look for possible signs of compositeness.
Axis error includes +- 1/1 contribution (The overall uncertainty in the bin-to-bin polar acceptance due to shower corrections, trigger and reconstruction efficiencies was estimated to be less than 1% and was added in quadrature to the statistical errorsData have been corrected for qed radiative effects up to order alpha**3 (F.A.Berends, R.Kleiss, Nucl.Phys.B206(1983)61)//Weak radiative corrections have not yet been provided in a form of a Monte Carlo generator program, but are estimated to be negligible at PETRA energies (M.Bohm, A.Denner, W.Hollik, DESY-86-165)).
Axis error includes +- 1/1 contribution (The overall uncertainty in the bin-to-bin polar acceptance due to shower corrections, trigger and reconstruction efficiencies was estimated to be less than 1% and was added in quadrature to the statistical errorsData have been corrected for qed radiative effects up to order alpha**3 (F.A.Berends, R.Kleiss, Nucl.Phys.B206(1983)61)//Weak radiative corrections have not yet been provided in a form of a Monte Carlo generator program, but are estimated to be negligible at PETRA energies (M.Bohm, A.Denner, W.Hollik, DESY-86-165)).
Axis error includes +- 1/1 contribution (The overall uncertainty in the bin-to-bin polar acceptance due to shower corrections, trigger and reconstruction efficiencies was estimated to be less than 1% and was added in quadrature to the statistical errorsData have been corrected for qed radiative effects up to order alpha**3 (F.A.Berends, R.Kleiss, Nucl.Phys.B206(1983)61)//Weak radiative corrections have not yet been provided in a form of a Monte Carlo generator program, but are estimated to be negligible at PETRA energies (M.Bohm, A.Denner, W.Hollik, DESY-86-165)).
e + e − annihilation into hadrons was studied at CM energies between 39.8 and 45.2 GeV and a search was made for new heavy quarks. No evidence was found for the existence of a narrow state excluding the possible existence of the lowest vector toponium state in this mass range. A search for continuum production of heavy quarks led to lower mass limits for new quarks of 22.0 GeV ( e Q = 2 3 ) and 21.0 GeV ( e Q = 1 3 ). Quarks are found to be pointlike, the corresponding mass parameter being larger than 288 GeV. A fit of the QCD and the electroweak contributions to R = σ tot / σ μμ yielded sin 2 θ W = 0.30 −0.07 +0.23 .
STATISTICAL ERRORS ONLY. NUMERICAL VALUES OF DATA TAKEN FROM PREPRINT.
No description provided.
No description provided.
The total cross section for the process e + e − → hadrons has been measured in the CM energy range between 12.0 and 36.4 GeV using the JADE detector with a typical systematic error of ±3%. The ratio R( σ( ee → hadrons ) σ pt ) is found to be constant over this range with an average value of 3.97 ± 0.05 (statistical and point-to-point systematic error) ± 0.10 (normalization error). The data were compared with the standard electro-weak interaction model including QCD corrections.
ERRORS ARE STATISTICAL PLUS POINT TO POINT SYSTEMATICS. THERE IS AN ADDITIONAL 2.4 PCT OVERALL NORMALIZATION ERROR.
No description provided.
A high statistics experiment was performed on Bhabha scattering at energies between 14 and 34 GeV. Good agreement with QED was observed. The combined data on Bhabha scattering and μ pair production were found to agree with the standard theory of electroweak interaction giving sin 2 θ = 0.27 −0.07 +0.06 . Assuming for the Z 0 mass a value of 90 GeV the leptonic weak coupling constants were determined to g V 2 = −0.04 ± 0.06 and g A 2 = 0.35 ± 0.09. A search for scalar leptons sets lower limits on the mass of scalar electrons of M s e > 16.6 GeV and of scalar muons of M s μ > 16.4 GeV.
No description provided.
No description provided.
Forum