A measurement of the inclusive charmless semileptonic branching fraction of beauty hadrons, $\mathrm{b}\rightarrow\mathrm{X}_\mathrm{u }\ell\nu$, has been performed using almost two million hadronic ...Z decays collected by the L3 experiment at LEP, yielding the result: \begin{displaymath} \mathrm{Br}(\mathrm{b}\rightarrow\mathrm{X}_\mathr m{u}\ell\nu) = (3.3 \pm 1.0 \pm 1.7)\times 10^{-3}. \end{displaymath} The first uncertainty is statistical and the second is systematic. The modulus of the Cabibbo-Kobayashi-Maskawa matrix element $\mathrm{V_{ub}}$ extracted from this measurement is: \begin{displaymath} |\mathrm{V_{ub}}| = (6.0\, ^{+0.8}_{-1.0} \, ^{+1.4}_{-1.9} \pm 0.2)\times 10^{-3}, \end{displaymath} where the uncertainties are statistical, systematic and theoretical, respectively.
Four of the Michel parameters and the average tau-neutrino helicity have been measured by analysing tau decay spectra in 147 \pb ~of data collected by the L3 detector. The decays \tte, ~\ttm, ~\ttp, ...~\ttr ~and their charge conjugates were considered. The results: $\rho = 0.762 \pm 0.035$, $\eta = 0.27 \pm 0.14$, $\xi = 0.70 \pm 0.16$, $\xi\delta = 0.70 \pm0.11$ and $\xi_{h} = -1.032 \pm 0.031$ are consistent with a V$-$A structure for the weak charged current and lepton universality.
We report on a study of single W boson production in a data sample collected by the L3 detector at centre-of-mass energies from 130 to 183 GeV. The signal consists of large missing energy final ...states with a single energetic lepton or two hadronic jets. The measured cross sections at five different centre-of-mass energies are consistent with the Standard Model expectations. The following limits on the anomalous WW$\gamma$ gauge couplings are derived at 95\% CL: $-0.46 \Delta \kappa_\gamma 0.57$ and $-0.86 \lambda_\gamma 0.75$.
A search for unstable neutral and charged heavy leptons as well as for stable charged heavy leptons has been made at center-of-mass energies $\sqrt{s}$ = 161 GeV and $\sqrt{s}$ = 172 GeV with the L3 ...detector at LEP. No evidence for their existence was found. We exclude unstable neutral leptons of Dirac (Majorana) type for masses below 78.0 (66.7), 78.0 (66.7) and 72.2 (58.2) GeV, if the heavy neutrino couples to the electron, muon or tau family, respectively. We exclude unstable charged heavy leptons for masses below 81.0 GeV for a wide mass range of the associated neutral heavy lepton. The production of stable charged heavy leptons with a mass less than 84.2 GeV is also excluded. If the unstable charged heavy lepton decays via mixing into a massless neutrino, we exclude masses below 78.7 GeV.
A search for the Standard Model Higgs boson has been performed with the L3 detector at LEP. The data sample was collected at three centre-of-mass energies, 161.3, 170.3 and 172.3 GeV with integrated ...luminosities of 10.8, 1.0 and 9.2 $pb^-1$, respectively. No Higgs signal is observed. In combination with previous data taken at the Z resonance, a lower Higgs mass limit, $M_H 69.5$ GeV, is obtained at 95\% confidence level.
A search for excited leptons $\rm e^*,~\mu^*, ~\tau^*$ and $\nu_{\rm e}^*$ in $\rm e^+e^-$ collisions at $\rm \sqrt{s}$ = 161 GeV is performed using the $\rm 10.8 ~pb^{-1}$ of data collected by the ...L3 detector at LEP. No evidence has been found for their existence. From an analysis of the expected $\ell^*\ell^*$ pair production in the channels $\rm ee\gamma\gamma$, $\rm \mu\mu\gamma\gamma$, $\rm \tau\tau\gamma\gamma$, $\rm eeWW$, and $\rm \nu\nu\gamma\gamma$, the lower mass limits at 95\% C.L. are 79.7 GeV for $\rm e^{*}$, 79.9 GeV for $\mu^{*}$, 79.3 GeV for $\tau^{*}$ and 71.3 GeV for $\nu_{\rm e}^{*}$ assuming the same couplings as for standard leptons. From an analysis of the expected $\ell\ell^*$ single production in channels $\rm ee\gamma$, $\mu\mu\gamma$, $ \tau\tau\gamma$, $\rm \nu_{e}eW$ and $\nu\nu\gamma$, the upper limits on the couplings $\lambda/m_{\ell^*}$ up to $m_{\ell^{*}}$ = 161 GeV are determined.
A search for single and multi-photon events with missing energy is performed using data collected at centre-of-mass energies between 161 GeV and 172 GeV for a total of 20.9 pb$^{-1}$ of integrated ...luminosity. The results obtained are used to derive the value for the $\nu\bar{\nu}\gamma(\gamma)$ cross section as well as upper limits on new physics processes.
We report on measurements of $\mathrm{e^+e^-}$ annihilation into hadrons and lepton pairs. The data have been taken with the L3 detector at LEP at centre--of--mass energies between ...161~$\mathrm{Ge\kern -0.12em V}$ and 172~$\mathrm{Ge\kern -0.12em V}$. In a data sample corresponding to 21.2~pb$^{-1}$ of integrated luminosity 2728 hadronic and 868 lepton--pair events are selected. The measured cross sections and leptonic forward--backward asymmetries agree well with the Standard Model predictions. \end{abstract}
We report on the measurement of W-boson pair-production with the L3 detector at LEP at a centre-of-mass energy of 161.34~\GeV. In a data sample corresponding to a total luminosity of 11~pb$^{-1}$, we ...select four-fermion events with high invariant masses of pairs of hadronic jets or leptons. Combining all final states, the measured total cross section for W-pair production is: $\SWW = 2.89^{+0.81}_{-0.70}~(stat.)\pm0.14~(syst.)$~pb. Within the Standard Model, this corresponds to a mass of the W boson of: $\MW = 80.80^{+0.48}_{-0.42}~(exp.)\pm 0.03$~(LEP)~\GeV. Limits on anomalous triple-vector-boson couplings are derived. \end{abstract}
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