Test of the τ-model of Bose–Einstein correlations and reconstruction of the source function in hadronic Z-boson decay at LEP

Bose–Einstein correlations of pairs of identical charged pions produced in hadronic Z decays are analyzed in terms of various parametrizations. A good description is achieved using a Lévy stable distribution in conjunction with a model where a particle’s momentum is correlated with its space–time point of production, the τ-model. Using this description and the measured rapidity and transverse momentum distributions, the space–time evolution of particle emission in two-jet events is reconstructed. However, the elongation of the particle emission region previously observed is not accommodated in the τ-model, and this is investigated using an ad hoc modification

Study of the solar anisotropy of cosmic ray primaries of about 200 GeV energy with the L3+C muon detector

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

Inclusive charged hadron production in two-photon collisions at LEP

Inclusive charged hadron production, e+e−→e+e−h±X, is studied using 414 pb^(−1) of data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 202 GeV. Single particle inclusive differential cross sections are measured as a function of the particle transverse momentum, pt, and pseudo-rapidity, η. For pt⩽1.5 GeV, the data are well described by an exponential, typical of soft hadronic processes. For higher pt, the onset of perturbative QCD processes is observed. The π± production cross section for pt>5 GeV is much higher than the NLO QCD predictions

Muon-pair and tau-pair production in two-photon collisions at LEP

The QED processes e^+e^−→e^+e^−μ^+μ^− and e^+e^−→e^+e^−τ^+τ^− are studied with the L3 detector at LEP using an untagged data sample collected at centre-of-mass energies 161 GeV⩽√s⩽209 GeV. The τ-pairs are observed through the associated decay of one τ into eνν and the other into ππν. The cross sections are measured as a function of √s. For muon pairs, the cross section of the γγ→μ^+μ^− process is also measured as a function of the two-photon centre-of-mass energy for 3 GeV⩽W_(γγ)⩽40 GeV. Good agreement is found between these measurements and th

Electroweak measurements in electron–positron collisions at W-boson-pair energies at LEP

Electroweak measurements performed with data taken at the electron–positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb^(−1) collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron–positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose–Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, m_W and Γ_W, the branching fraction of W decays to hadrons, B(W → had), and the trilinear gauge-boson self-couplings g^z_1, κ_γ and λ_γ are determined to be: M_W = 80.376 ± 0.0333 GeV Γ_W = 2.195 ± 0.083 GeV B(W → had) = 67.41 ± 0.27% g^z_1 = 0.984^(+0.018)_(-0.020) κ_γ = 0.982 ± 0.042 λ_γ = -0.022 ± 0.01

Study of hadronic event shape in flavour tagged events in e^+e^- annihilation at ^(⟨s√⟩) = 197 GeV

Results are presented from a study of the structure of hadronic events in high-energy e^+e^- interactions detected by the L3 detector at LEP. Various event shape distributions and their moments are measured at several energy points at and above the Z-boson mass. The event flavour is tagged by using the decay characteristics of b-hadrons. Measurements of distributions of event shape variables for all hadronic events, for light (u, d, s, c) and heavy (b) quark flavours are compared to several QCD models with improved leading log approximation: JETSET, HERWIG and ARIADNE. A good description of the data is provided by the models

Muon-pair and tau-pair production in two-photon collisions at LEP

The QED processes e^+e^−→e^+e^−μ^+μ^− and e^+e^−→e^+e^−τ^+τ^− are studied with the L3 detector at LEP using an untagged data sample collected at centre-of-mass energies 161 GeV⩽√s⩽209 GeV. The τ-pairs are observed through the associated decay of one τ into eνν and the other into ππν. The cross sections are measured as a function of √s. For muon pairs, the cross section of the γγ→μ^+μ^− process is also measured as a function of the two-photon centre-of-mass energy for 3 GeV⩽W_(γγ)⩽40 GeV. Good agreement is found between these measurements and th

Inclusive charged hadron production in two-photon collisions at LEP

Inclusive charged hadron production, e+e−→e+e−h±X, is studied using 414 pb^(−1) of data collected at LEP with the L3 detector at centre-of-mass energies between 189 and 202 GeV. Single particle inclusive differential cross sections are measured as a function of the particle transverse momentum, pt, and pseudo-rapidity, η. For pt⩽1.5 GeV, the data are well described by an exponential, typical of soft hadronic processes. For higher pt, the onset of perturbative QCD processes is observed. The π± production cross section for pt>5 GeV is much higher than the NLO QCD predictions