The process e+ e- -> e+ e- Z/gamma* is studied with the OPAL detector at LEP at a centre of mass energy of sqrt(s) = 189 GeV. The cross-section times the branching ratio of the Z/gamma* decaying into hadrons is measured within Lorentz invariant kinematic limits to be (1.2 +/- 0.3 +/- 0.1) pb for invariant masses of the hadronic system between 5 GeV and 60 GeV and (0.7 +/- 0.2 +/- 0.1) pb for hadronic masses above 60 GeV. The differential cross-sections of the Mandelstam variables s-hat, t-hat, and u-hat are measured and compared with the predictions from the Monte Carlo generators grc4f and PYTHIA. From this, based on a factorisation ansatz, the total and differential cross-sections for the subprocess e gamma -> e Z/gamma* are derived.
Measured values of the cross section times the branching ratio for the (Z0/GAMMA*) decay into hadrons within the restricted kinematic limits.
Differential cross-section dsig_ee/dm_qq.
Differential cross-section dsigma_ee/dsqrt(shat).
The production of $J/\psi$ mesons in continuum $e^+e^-$ annihilations has been studied with the BABAR detector at energies near the $\Upsilon(4S)$ resonance, approximately 10.6 GeV. The mesons are distinguished from $J/\psi$ production in B decays through their center-of-mass momentum and energy. We measure the cross section $e^+e^-\to J/\psi X$ to be $2.52\pm 0.21\pm 0.21$ pb: for momentum above 2 GeV/c, it is $1.87\pm 0.10\pm 0.15$ pb. We set a 90% confidence level upper limit on the branching fraction for direct $\Upsilon(4S)$\to J/\psi X$ decays at $4.7\times 10^{-4}$.
Cross section measurement.
The cross-sections for the production of single charged and neutral intermediate vector bosons were measured using integrated luminosities of 52 pb^{-1} and 154 pb^{-1} collected by the DELPHI experiment at centre-of-mass energies of 182.6 GeV and 188.6 GeV, respectively. The cross-sections for the reactions were determined in limited kinematic regions. The results found are in agreement with the Standard Model predictions for these channels.
Cross sections for single-W production in the (E- NUEBAR Q QBAR + CC) and (E- NUEBAR LEPTON LEPTONBAR) + CC) channels.
Cross sections for the E NU E NU channel, which includes contributions from both single-W and from single-Z0 with a large interference bewteen the two processes.
Cross sections for single-Z0 production in the hadronic channel.
The fragmentation of b quarks into B mesons is studied with four million hadronic Z decays collected by the ALEPH experiment during the years 1991-1995. A semi-exclusive reconstruction of B->l nu D(*) decays is performed, by combining lepton candidates with fully reconstructed D(*) mesons while the neutrino energy is estimated from the missing energy of the event. The mean value of xewd, the energy of the weakly-decaying B meson normalised to the beam energy, is found to be mxewd = 0.716 +- 0.006 (stat) +- 0.006 (syst) using a model-independent method; the corresponding value for the energy of the leading B meson is mxel = 0.736 +- 0.006 (stat) +- 0.006 (syst). The reconstructed spectra are compared with different fragmentation models.
Normalized binned spectra for weakly-decaying (WD) leading (L) B-mesons.
The extracted spectra spectra for weakly-decaying (WD) leading (L) B-mesons.
Statistical error matrix for the Weakly Decaying distribution in units of 10**-6.
Using the Belle detector operating at the KEKB e+e- storage ring, we have measured the mean multiplicity and the momentum spectrum of neutral pions from the decays of the Upsilon(4S) resonance. We measure a mean of 4.70 +/- 0.04 +/- 0.22 neutral pions per Upsilon(4S) decay.
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
No description provided.
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.
We have measured gluon splitting into bottom quarks, g→b b ̄ , in hadronic Z 0 decays collected by SLD between 1996 and 1998. The analysis was performed by looking for secondary bottom production in 4-jet events of any primary flavor. 4-jet events were identified, and in each event a topological vertex-mass technique was applied to the two jets closest in angle in order to identify them as b or b ̄ jets. The upgraded CCD-based vertex detector gives very high B -tagging efficiency, especially for B hadrons with the low energies typical of this process. We measured the rate of g→b b ̄ production per hadronic event, g b b ̄ , to be (2.44±0.59(stat.)±0.34(syst.))×10 −3 .
No description provided.
We report values of $R = \sigma(e^+e^-\to {hadrons})/\sigma(e^+e^-\to\mu^+\mu^-)$ for 85 center-of-mass energies between 2 and 5 GeV measured with the upgraded Beijing Spectrometer at the Beijing Electron-Positron Collider.
Measured values of R.
The triple gauge-boson couplings involving the W are determined using data samples collected with the ALEPH detector at mean centre-of-mass energies of 183 GeV and 189 GeV, corresponding to integrated luminosities of 57 pb^-1 and 174 pb^-1, respectively. The couplings, g^Z_1, Kappa_gamma and lambda_gamma, are measured using W-pair events, single-W production and single-gamma production. Each coupling is measured individually with the other two coupling fixed at their Standard Model value. Including ALEPH results from lower energies, the 95% confidence level intervals for the deviation to the Standard Model are -0.087 < Dg^Z_1 < 0.141 -0.200 < DKappa_gamma < 0.258 -0.062 < Lambda_gamma < 0.147. Fits are also presented where two or all three couplings are allowed to vary. In addition, W-pair events are used to set limits on the C- or P-violating couplings g^V_4, g^V_5, Kappa_V, and Lambda_V, where V denotes either gamma or Z. No deviations from the Standard Model expectations are observed.
The errors included the statistical and systematic uncertainties. Deviation from SM values.
The errors included the statistical and systematic uncertainties. Combined results, lower sqrt(s) data are also included.
The errors included the statistical and systematic uncertainties. Combined results, lower sqrt(s) data are also included. Three-parameter fit.
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