Search results

3,378 records were found.

We present the results of a search for nu_mu → nu_e oscillations in the NOMAD experiment at Cern. The experiment looked for the appearance of nu_e in a predominantly nu_mu wide-band neutrino beam at the CERN SPS. No evidence for oscillations was found. The 90% confidence limits obtained are Delta m^2 < 0.4 eV^2 for maximal mixing and sin^2(2theta) < 1.4 X 10^-3 for large Delta m^2. This result excludes the LSND allowed region of oscillation parameters with Delta m^2 >~ 10 eV^2.
We show that the sum rule recently proved by Uraltsev in the heavy quark limit of QCD holds in relativistic quark models \à la Bakamjian and Thomas, that were already shown to satisfy Isgur-Wise scaling and Bjorken sum rule. This new sum rule provides a {\\it rationale} for the lower bound of the slope of the elastic IW function $\\rho^2 \\geq {3 \\over 4}$ obtained within the BT formalism some years ago. Uraltsev sum rule suggests an inequality $|\\tau_{3/2}(1)| > |\\tau_{1/2}(1)|$. This difference is interpreted in the BT formalism as due to the Wigner rotation of the light quark spin, independently of a possible LS force. In BT models, the sum rule convergence is very fast, the $n = 0$ state giving the essential contribution in most of the phenomenological potential models. We underline that there is a serious problem, in the heavy ...
A study of neutral-current four-fermion processes is performed, using data collected by the L3 detector at LEP during high-energy runs at centre-of-mass energies 130 - 136, 161 and 170 - 172 GeV, with integrated luminosities of 4.9, 10.7 and 10.1 pb$^{-1}$, respectively. The total cross sections for the final states $ \ell\ell \ell^\prime \ell^\prime $ and $\rm \ell\ell qq $ ($\ell$,~$\ell^\prime $ = e, $\mu$ or $\tau$) are measured and found to be in agreement with the Standard Model prediction.
Bose-Einstein correlations in W-pair decays are studied using data collected by the ALEPH detector at LEP at e+e- centre-of-mass energies from 183 to 209 GeV. The analysis is based on the comparison of WW-->qqqq events to ``mixed'' events constructed with the hadronic part of WW-->qqlnu events. The data are in agreement with the hypothesis that Bose-Einstein correlations are present only for pions from the same W decay. The JETSET model with Bose-Einstein correlations between pions from different W bosons is disfavoured.
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.
The reaction $\mathrm{e}^{+} \mathrm{e}^{-} \rightarrow \mathrm{e}^{+} \mathrm{e}^{-} \gamma ^{*} \gamma ^{*} \rightarrow \mathrm{e}^{+} \mathrm{e}^{-} $ {\sl hadrons} is analysed using data collected by the L3 detector during the LEP runs at $\sqrt {s}$ = 130-140 GeV and $\sqrt {s}$ = 161 GeV. The cross sections $\sigma(\mathrm{e}^{+} \mathrm{e}^{-} \rightarrow \mathrm{e}^{+} \mathrm{e}^{-} $ {\sl hadrons}) and $\sigma (\gamma\gamma \rightarrow $ {\sl hadrons}) are measured in the interval 5 $\leq W_{\gamma\gamma} \leq$ 75 GeV. The energy dependence of the $\sigma (\gamma\gamma \rightarrow $ {\sl hadrons}) cross section is consistent with the universal Regge behaviour of total hadronic cross sections. %\end{abstract}
We report on the observation of single W boson production in a data sample collected by the L3 detector at LEP2. The signal consists of large missing energy final states with a single energetic lepton or two hadronic jets. The cross-section is measured to be $0.61^{+0.43}_{-0.33} \pm 0.05 \; \rm{pb}$ at the centre of mass energy $\sqrt{s}=172 \GeV{}$, consistent with the Standard Model expectation. From this measurement the following limits on the anomalous $\gamma$WW gauge couplings are derived at 95\% CL: $\rm -3.6 \Delta \kappa_\gamma 1.5$ and $\rm -3.6 \lambda_\gamma 3.6$.
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.
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