We measure three-particle Bose–Einstein correlations in hadronic Z decay with the L3 detector at LEP. Genuine three-particle Bose–Einstein correlations are observed. By comparing two- and ...three-particle correlations we find that the data are consistent with fully incoherent pion production.
Aims.Several experiments have reported observations on possible correlations between the flux of high energy muons and intense solar flares. If confirmed, these observations would have significant ...implications for acceleration processes in the heliosphere able to accelerate protons and other ions to energies of at least tens of GeV. Methods: .The solar flare of the 14 of July 2000 offered a unique opportunity for the L3+C experiment to search for a correlated enhancement in the flux of muons using the L3 precision muon spectrometer. Its capabilities for observing a directional excess in the flux of muons above 15 GeV (corresponding to primary proton energies above 40 GeV) are presented along with observations made on the 14th of July 2000. Results: .We report an excess which appeared at a time coincident with the peak increase of solar protons observed at lower energies. The probability that the excess is a background fluctuation is estimated to be 1%. No similar excess of the muon flux was observed up to 1.5 h after the solar flare time.
Data collected at LEP at centre-of-mass energies \(\sqrt{s} = 189-209\) GeV are used to study correlations of the spin of W bosons using \(\mathrm{e}^ + \mathrm{e}^-\to \mathrm{W}^ + \mathrm{W}^-\to ...{\ensuremath{\ell\nu\mathrm{q\bar{q}}}\) events. Spin correlations are favoured by data, and found to agree with the Standard Model predictions. In addition, correlations between the W-boson decay planes are studied in \(\mathrm{e}^ + \mathrm{e}^-{}\to{}\mathrm{W}^ + \mathrm{W}^- \to{}{\ensuremath{\ell\nu\mathrm{q\bar{q}}}\) and \(\mathrm{e}^ + \mathrm{e}^-{}\to{}\mathrm{W}^ + \mathrm{W}^-{}\to{}{\ensuremath{\text{q}\bar{\text{q}}\text{q}\bar{\text{q}}}{}\) events. Decay-plane correlations are measured to be consistent with the Standard Model predictions.
Hadron production and lepton-pair production in e+e- collisions are studied with data collected with the L3 detector at LEP at centre-of-mass energies sqrt{s}=192-208GeV. Using a total integrated ...luminosity of 453/pb, 36057 hadronic events and 12863 lepton-pair events are selected. The cross sections for hadron production and lepton-pair production are measured for the full sample and for events where no high-energy initial-state-radiation photon is emitted prior to the collisions. Lepton-pair events are further investigated and forward-backward asymmetries are measured. Finally, the differential cross sections for electron-positron pair-production is determined as a function of the scattering angle. An overall good agreement is found with Standard Model predictions.
Open charm production in
γγ collisions is studied with data collected at e
+e
− centre-of-mass energies from 189 GeV to 202 GeV corresponding to a total integrated luminosity of 410 pb
−1. The charm ...cross section
σ(γγ→
c
c
̄
X
) is measured for the first time as a function of the two-photon centre-of-mass energy in the interval from 5 GeV to 70 GeV and is compared to NLO QCD calculations.
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^- _ rightarrow $e^+e^-bb^-X$ 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 e$^+e^- \to e^+e^-$ hadrons reaction, where one of the two electrons is detected in a low polar-angle calorimeter, is analysed in order to measure the hadronic photon structure function ...$F^\gamma_2$ . The full high-energy and high-luminosity data set, collected with the L3 detector at centre-of-mass energies 189 GeV $\leq \sqrt{s} \leq$ 209 GeV, corresponding to an integrated luminosity of 608/pb is used. The Q$^2$ range 11 GeV$^2 \leq Q^2$ 34 GeV$^2$ and the $x$ range 0.006$\leq x \leq$ 0.556 are considered. The data are compared with recent parton density functions.
An overview is given of the study of final state interactions in hadronically
decaying W pairs produced in e^+e^--collisions as it is performed by the four
LEP experiments. Bose-Einstein correlations ...are investigated by comparing like-
with unlike-signed pairs of pions and/or using the mixed event analysis
technique. Colour reconnection is examined with a method that compares the
particle flow distributions in inter-jet regions.
In this Report, QCD results obtained from a study of hadronic event structure in high energy e^+e^- interactions with the L3 detector are presented. The operation of the LEP collider at many ...different collision energies from 91 GeV to 209 GeV offers a unique opportunity to test QCD by measuring the energy dependence of different observables. The main results concern the measurement of the strong coupling constant, \alpha_s, from hadronic event shapes and the study of effects of soft gluon coherence through charged particle multiplicity and momentum distributions.
The absolute muon flux between 20 GeV and 300 GeV is measured with the L3 magnetic muon spectrometer for zenith angles ranging from 0 degree to 58 degrees. Due to the large exposure of about 150 m2 ...sr d, and the excellent momentum resolution of the L3 muon chambers, a precision of 2.3% at 150 GeV in the vertical direction is achieved. The ratio of positive to negative muons is studied between 20 GeV and 500 GeV, and the average vertical muon charge ratio is found to be 1.285 +- 0.003 (stat.)+- 0.019 (syst.).
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