Inclusive branching ratios involving b to tau transitions are measured in approximately four million hadronic Z decays collected by the ALEPH detector at LEP. The fully-inclusive branching ratio b -> tau nu X and the semi-inclusive branching ratio b -> tau nu D*+/- X are measured to be (2.43 +/- 0.20 +/- 0.25)% and (0.88 +/- 0.31 +/- 0.28)%, in agreement with the standard model predictions. Upper limits on the branching fractions b -> tau nu and b -> s nu nubar are set to 8.3 10**-4 and 6.4 10**-4 at the 90% C.L. These results allow a 90% C.L. lower limit of 0.40 (GeV/c**2)**-1 to be set on the tan(beta)/mH+/- ratio, in the framework of type-II two-Higgs-doublet mode
TAN(BETA) is the two-Higgs-doublet model parameter, while M_H is the mass of charged Higgs.
Measurements are presented of the polarisation of W+W- boson pairs produced in e+e- collisions, and of CP-violating WWZ and WWGamma trilinear gauge couplings. The data were recorded by the OPAL experiment at LEP during 1998, where a total integrated luminosity of 183 pb^-1 was obtained at a centre-of-mass energy of 189 GeV. The measurements are performed through a spin density matrix analysis of the W boson decay products. The fraction of W bosons produced with longitudinal polarisation was found to be sigma_L/sigma_total = (21.0 +- 3.3 +- 1.6)% where the first error is statistical and the second systematic. The joint W boson pair production fractions were found to be sigma_TT/sigma_total = (78.1 +- 9.0 +- 3.2) %, sigma_LL/sigma_total = (20.1 +- 7.2 +- 1.8) % and sigma_TL/sigma_total = (1.8 +- 14.7 +- 3.8) %. In the CP-violating trilinear gauge coupling sector we find kappa_z = -0.20 +0.10 -0.07, g^z_4 = -0.02 +0.32 -0.33 and lambda_z = -0.18 +0.24 -0.16, where errors include both statistical and systematic uncertainties. In each case the coupling is determined with all other couplings set to their Standard Model values except those related to the measured coupling via SU(2)_LxU(1)_Y symmetry. These results are consistent with Standard Model expectations.
Individual W-boson transverse polarised cross-sections.
Individual W-boson longitudinal polarised cross-sections.
W pair polarized cross-sections. (C=TT), (C=LL), and (C=TL) stand for both W transversely polarised, for both W longitudinally polarised, and for transversely and longitudinally polarisedW-bosons, respectively.
The data collected by the L3 experiment at LEP at a centre-of-mass energy of 188.6 GeV are used to measure the W-pair production cross section and the W-boson decay branching fractions. These data correspond to an integrated luminosity of 176.8pb^-1. The total cross section for W-pair production, combining all final states, is measured to be sigma_WW = 16.24 +/- 0.37(stat.) +/- 0.22(syst.) pb. Including our data collected at lower centre-of-mass energies, the hadronic branching fraction of the W-boson is determined to be B(W ->qq) = [68.20 +/- 0.68 (stat.) +/- 0.33 (syst.) ] %. The results agree with the Standard Model predictions.
Quoted cross sections with W-boson decays (i.e. W +- < ... >) mean the cross sections times the corresponding branching ratios.
VCS is the CKM matrix element.
Single W boson production in electron-positron collisions is studied with the L3 detector at LEP. The data sample collected at a centre-of-mass energy of \sqrt{s} = 188.7GeV corresponds to an integrated luminosity of 176.4pb^-1. Events with a single energetic lepton or two acoplanar hadronic jets are selected. Within phase-space cuts, the total cross-section is measured to be 0.53 +/- 0.12 +/- 0.03 pb, consistent with the Standard Model expectation. Including our single W boson results obtained at lower \sqrt{s}, the WWgamma gauge couplings kappa_gamma and lambda_gamma are determined to be kappa_gamma = 0.93 +/- 0.16 +/- 0.09 and lambda_gamma = -0.31 +0.68 -0.19 +/- 0.13.
No description provided.
No description provided.
No description provided.
Using the ARGUS detector at the e+e- storage ring DORIS II, we have searched for the real and imaginary part of the electric dipole formfactor d_tau of the tau lepton in the production of tau pairs at q^2=100 GeV^2. This is the first direct measurement of this CP violating formfactor. We applied the method of optimised observables which takes into account all available information on the observed tau decay products. No evidence for CP violation was found, and we derive the following results: Re(d_tau)=(1.6+-.9)*10^(-16) ecm and Im(d_tau)=(-0.2+-0.8)*10^(-16) ecm, where statistical and systematic errors have been combined.
Electric dipole moment in E(electric charge)*CM units. Systematic and statistical errors are added in quadrature.
The production of W-pairs is analysed in a data sample collected by ALEPH at a mean centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 174.2 pb^-1. Cross sections are given for different topologies of W decays into leptons or hadrons. Combining all final states and assuming Standard Model branching fractions, the total W-pair cross section is measured to be 15.71 +- 0.34 (stat) +- 0.18 (syst) pb. Using also the W-pair data samples collected by ALEPH at lower centre-of-mass energies, the decay branching fraction of the W boson into hadrons is measured to be BR (W > hadrons) = 66.97 +- 0.65 (stat) +- 0.32 (syst) %, allowing a determination of the CKM matrix element |V(cs)|= 0.951 +- 0.030 (stat) +- 0.015 (syst).
Total W+ W- production cross section.
Cross section for the fully leptonic decay channels.
Results of cross sections for decays into the different topological decay channels.
We report on measurements of hadronic and leptonic cross sections and leptonic forward-backward asymmetries performed with the L3 detector in the years 1993-95. A total luminosity of 103 pb^-1 was collected at centre-of-mass energies \sqrt{s} ~ m_Z and \sqrt{s} ~ m_Z +/- 1.8 GeV which corresponds to 2.5 million hadronic and 245 thousand leptonic events selected. These data lead to a significantly improved determination of Z parameters. From the total cross sections, combined with our measurements in 1990-92, we obtain the final results: m_Z = 91189.8 +/- 3.1 MeV, Gamma_Z = 2502.4 +/- 4.2 MeV, Gamma_had = 1741.1 +/- 3.8 MeV, Gamma_l = 84.14 +/- 0.17 MeV. An invisible width of Gamma_inv = 499.1 +/- 2.9 MeV is derived which in the Standard Model yields for the number of light neutrino species N_nu = 2.978 +/- 0.014. Adding our results on the leptonic forward-backward asymmetries and the tau polarisation, the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons are determined to be \bar{g}_V^l = -0.0397 +/- 0.0017 and \bar{g}_A^l = -0.50153 +/- 0.00053.Including our measurements of the Z -> b \bar{b} forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of sin^2\bar{\theta}_W = 0.23093 +/- 0.00066 is derived. All these measurements are in good agreement with the Standard Model of electroweak interactions. Using all our measurements of electroweak observables an upper limit on the mass of the Standard Model Higgs boson of m_H < 133 GeV is set at 95% confidence level.
Updated values of coupling constants and electroweak mixing angle.
Cross sections for hadron production from the 1993 data. The first DSYS error is the uncorrelated part of the systematic error. The second DSYS error is from the statistical error on the absolute luminosity. In addition there is a fully correlated multiplicative contribution to the systematic error of 0.039 PCT plus an absolute uncertainty of 3.2pb together with an additional error from the absolute luminosity of 0.105 PCT.
Cross sections for hadron production from the 1994 data. The first DSYS error is the uncorrelated part of the systematic error. The second DSYS error is from the statistical error on the absolute luminosity. In addition there is a fully correlated multiplicative contribution to the systematic error of 0.039 PCT plus an absolute uncertainty of 3.2pb together with an additional error from the absolute luminosity of 0.088 PCT.
An analysis of the data collected in 1997 and 1998 with the DELPHI detector at e+e- collision energies close to 183 and 189 GeV was performed in order to extract the hadronic and leptonic fermion-pair cross-sections, as well as the leptonic forward-backward asymmetries and angular distributions. The data are used to put limit on contact interactions between fermions, the exchange of R-parity violating SUSY sneutrinos, Z' bosons and the existence of gravity in extra dimensions.
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
Hadronic cross section measured with the 1993 data. Additional systematic error of 0.10 PCT (efficiencies and backgrounds) and 0.29 PCT (absolute luminosity).
Hadronic cross section measured with the 1994 data. Additional systematic error of 0.11 PCT (efficiencies and backgrounds) and 0.11 PCT (absolute luminosity).
Hadronic cross section measured with the 1995 data. Additional systematic error of 0.10 PCT (efficiencies and backgrounds) and 0.11 PCT (absolute luminosity).
We report on measurements of e+e- annihilation into hadrons and lepton pairs. The data have been collected with the L3 detector at LEP at centre-of-mass energies between 130 and 189 GeV. Using a total integrated luminosity of 243.7 pb^-1, 25864 hadronic and 8573 lepton-pair events are selected for the measurement of cross sections and leptonic forward-backward asymmetries. The results are in good agreement with Standard Model predictions.
Measured cross sections for the hadronic events.
Measured cross sections for the muon-pair events.
Measured cross sections for the tau-pair events.
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