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We present a study of the inclusive $\omega$ and $\eta^{\prime}$ production based on 3.1 million hadronic Z decays recorded with the L3 detector at LEP during 1991--1994. The production rates per hadronic Z decay have been measured to be $1.17 \pm 0.17 $ $\omega$ mesons and $0.25 \pm 0.04 $ $\eta^{\prime}$ mesons. The production rates and the differential cross sections have been compared with predictions of the JETSET and the HERWIG Monte Carlo models. We have observed that the differential cross sections can be described by an analytical quantum chromodynamics calculation. \end{document}
We present a measurement of the average b-hadron lifetime ${\rm \tau_b}$ at the $\mathrm{e^+e^-} \, $ collider LEP. Using hadronic Z decays collected in the period from 1991 to 1994, two independent analyses have been performed. In the first one, the b-decay position is reconstructed as a secondary vertex of hadronic b-decay particles. The second analysis is an updated measurement of ${\rm \tau_b}$ using the impact parameter of leptons with high momentum and high transverse momentum. The combined result is \begin{center} ${\rm \tau_b= [ 1549 \pm 9 \, (stat) \, \pm 15 \, (syst) ] \; fs \,}$ . \end{center} In addition, we measure the average charged b-decay multiplicity ${\rm \langle n_{\rm b}} \rangle$ and the normalized average b-energy ${\rm \langle x_E \rangle_{\rm b}}$ at LEP to be \begin{center} ${\rm \langle n_{\rm b} \rangle = 4....
The measurements of hadron and lepton--pair production cross sections and lepton--pair forward--backward asymmetries performed with the L3 detector at centre--of--mass energies between 130 GeV and 172 GeV are used to search for new physics phenomena. New physics effects involving four fermion vertices -- contact interactions -- are looked for in all channels. For hadron production the exchange of virtual leptoquarks and scalar quarks is studied. No evidence for deviations from the Standard Model expectations is found. Lower limits on the scale $\Lambda$ of contact interactions in the range 1.2 -- 7.1 TeV are obtained at the 95\% confidence level for various models. Upper limits on the coupling strengths of leptoquarks and scalar quarks are derived.
An analysis of single and multi-photon events with missing energy is performed using data collected with the L3 detector at LEP at centre-of-mass energies around 183\gev, for a total of 55.3 pb$^{-1}$ of integrated luminosity. The results obtained are in good agreement with the Standard Model prediction and are used to derive the value for the $\epem\ra\nnbar\gamma(\gamma)$ cross section as well as upper limits on cross sections of new physics processes. Several interpretations in supersymmetric models providing new limits on the masses of the lightest neutralino and of the gravitino are presented.
New measurements at a centre-of-mass energy of 183 GeV of the hadronic photon structure function F2(x) in the Q2 interval, 9 GeV2 Q2 30 GeV2, are presented. The data, collected in 1997, with the L3 detector, correspond to an integrated luminosity of 51.9 pb-1. Combining with the data taken at centre-of-mass energies of 91 GeV, the evolution of F2 with Q2 is measured in the Q2 range from 1.2 GeV2 to 30 GeV2. F2 shows a linear growth with ln(Q2); the value of the slope (alpha-1)dF2(Q2)/dln(Q2) is measured in two x bins from 0.01 to 0.2 and is higher than predictions.
The tau lepton lifetime is measured with the L3 detector at LEP using the complete data taken at centre-of-mass energies around the Z pole resulting in $\tau_{\tau}\,=\,293.2\,\pm\,2.0~\mbox{(stat)}\,\pm\, 1.5~\mbox{(syst)}$ fs. The comparison of this result with the muon lifetime supports lepton universality of the weak charged current at the level of six per mille. Assuming lepton universality, the value of the strong coupling constant, $\alpha_s$ is found to be $\alpha_s(m_{\tau}^2)$ = 0.319 $\pm$ 0.015~\mbox{(exp)} $\pm$ 0.014~\mbox{(theory)}.
We have measured the probability, $\overline{n}_{\rm{g} \rightarrow c\overline{c}}$, of a gluon splitting into a charm-quark pair using 1.7 million hadronic Z decays collected by the L3 detector. Two independent methods have been applied to events with a three-jet topology. One method relies on tagging charmed hadrons by identifying a lepton in the lowest energy jet. The other method uses a neural network based on global event shape parameters. Combining both methods, we measure $\overline{n}_{\rm{g} \rightarrow c\overline{c} } = [2.45 \pm 0.29 \pm 0.53]\$.
The process e+e- -> W+ W- gamma is studied using the data collected by the L3 detector at LEP. New results, corresponding to an integrated luminosity of 427.4 pb-1 at centre-of-mass energies from 192 GeV to 207 GeV, are presented. The W+W- gamma cross sections are measured to be in agreement with Standard Model expectations. No hints of anomalous quartic gauge boson couplings are observed. Limits at 95% confidence level are derived using also the process e+e- --> nu nubar gamma gamma.
Single- and multi-photon events with missing energy are selected in 619 pb(-1) of data collected by the L3 detector at LEP at centre-of-mass energies between 189 and 209 GeV. The cross sections of the process e(+) e(-) nunugamma(gamma) are found to be in agreement with the Standard Model expectations, and the number of light neutrino species is determined, including lower energy data, to be N-nu = 2.98 +/- 0.05 +/- 0.04. Selection results are given in the form of tables which can be used to test future models involving single- and multi-photon signatures at LEP. These final states are also predicted by models with large extra dimensions and by several supersymmetric models. No evidence for such models is found. Among others, lower limits between 1.5 and 0.65 TeV are set. at 95% confidence level, on the new scale of gravity for the numb...
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