Context. Primary cosmic rays experience multiple deflections in the non-uniform galactic and heliospheric magnetic fields which may generate anisotropies. Aims. A study of anisotropies in the energy ...range between 100 and 500 GeV is performed. This energy range is not yet well explored. Methods. The L3 detector at the CERN electron-positron collider, LEP, is used for a study of the angular distribution of atmospheric muons with energies above 20 GeV. This distribution is used to investigate the isotropy of the time-dependent intensity of the primary cosmic-ray flux with a Fourier analysis. Results. A small deviation from isotropy at energies around 200 GeV is observed for the second harmonics at the solar frequency. No sidereal anisotropy is found at a level above 10-4. The measurements were performed in the years 1999 and 2000.
The reaction e+e- -> e+e- gamma* gamma* -> e+e- hadrons for quasi-real photons is studied using data from root(s) = 183 GeV up to 202 GeV. Results on the total cross sections sigma(e+e- -> e+e- ...hadrons) and sigma(+e- gamma* gamma* -> e+e- hadrons) are given for the two-photon centre-of-mass energies 5 GeV Wgammagamma 185 GeV. The total cross section of two real photons is described by a Regge parametrisation. We observe a steeper rise with the two-photon centre-of-mass energy as compared to the hadron-hadron and the photon-proton cross sections. The data are also compared to the expectations of different theoretical models.
The cross section for open-beauty production in photon–photon collisions is measured using the whole high-energy and high-luminosity data sample collected by the L3 detector at LEP. This corresponds ...to 627 pb−1 of integrated luminosity for electron–positron centre-of-mass energies from 189 to 209 GeV. Events containing b quarks are identified through their semi-leptonic decay into electrons or muons. The e+e−→e+e−bb¯X cross section is measured within our fiducial volume and then extrapolated to the full phase space. These results are found to be in significant excess with respect to Monte Carlo predictions and next-to-leading order QCD calculations.
The process e+e−→W+W−γ 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 to ...207 GeV, are presented.
The W+W−γ 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−→νν̄γγ.
Inclusive jet production, e+e−→e+e− jet X, is studied using 560 pb−1 of data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 209 GeV. The inclusive differential cross ...section is measured using a kt jet algorithm as a function of the jet transverse momentum, pt, in the range 3<pt<50 GeV for a pseudorapidity, η, in the range −1<η<1. This cross section is well represented by a power law. For high pt, the measured cross section is significantly higher than the NLO QCD predictions, as already observed for inclusive π± and π0 production.
We analyse e
+e
−→
ττγ events using
100
pb
−1
of data collected by the L3 experiment during the 1991-1995 LEP runs at the Z pole. From the energy of the photons and their isolation from the tau decay ...products, we determine the anomalous magnetic and electric dipole moments of the tau to be, respectively:
a
τ=0.004±0.027±0.023;
d
τ=(0.0±1.5±1.3)×10
−16e·
cm.
This is a direct measurement of these
τ form factors at
q
2=0.
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 \(103 {\rm ...pb}^{-1}\) was collected at centre-of-mass energies \(\sqrt s \approx m_{\rm Z}\) and \(\sqrt s \approx m_{\rm Z} \pm 1.8{\rm GeV}\) 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:An invisible width of \(\Gamma_{\rm inv} = 499.1\pm 2.9\,{\rm MeV}\) is derived which in the Standard Model yields for the number of light neutrino species \(N_{\nu} = 2.978\pm 0.014\). 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 \(\bar g^{\ell}_{\rm V}= -0.0397\pm 0.0017\) and \(\bar g^{\ell}_{\rm A} = -0.50153 \pm 0.00053\). Including our measurements of the \({\rm Z}\rightarrow{\rm b\bar b}\) forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of \(\sin^2 \bar \theta_{\rm W} = 0.23093 \pm 0.00066\) 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 \(m_{\rm H} < 133\) GeV is set at 95% confidence level.
Measurements of inclusive production of the Λ, Ξ- and Ξ*(1530) baryons in two-photon collisions with the L3 detector at LEP are presented. The inclusive differential cross sections for Λ and Ξ- are ...measured as a function of the baryon transverse momentum, pt, and pseudo-rapidity, η. The mean number of Λ, Ξ- and Ξ*(1530) baryons per hadronic two-photon event is determined in the kinematic range 0.4 GeV<pt<2.5 GeV, |η|<1.2. Overall agreement with the theoretical models and Monte Carlo predictions is observed. A search for inclusive production of the pentaquark θ+(1540) in two-photon collisions through the decay θ+→pK0S is also presented. No evidence for production of this state is found.
Bose–Einstein correlations in W-pair production at LEP are investigated in a data sample of 629 pb−1 collected by the L3 detector at s=189–209 GeV. Bose–Einstein correlations between pions within a W ...decay are observed and found to be in good agreement with those in light-quark Z decay. No evidence is found for Bose–Einstein correlations between hadrons coming from different W's in the same event.
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