275 research outputs found

    The gluon content of the pion from high-pt photon production

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    Aurenche P, Baier R, Fontannaz M, Kienzle-Focacci MN, Werlen M. The gluon content of the pion from high-pt photon production. Physics letters B. 1989;233(3-4):517-521

    Results on the calibration of the L3 BGO calorimeter with cosmic rays

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    Photon structure functions and azimuthal correlations of lepton pairs in tagged gamma gamma collisions RID C-4549-2008 RID C-5719-2008

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    Neutral-current four-fermion production in e(+)e(-) interactions at LEP

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    Neutral-current four-fermion production, e(+)e(-) f (f) over bar f\u27(f) over barf, is studied in 0.7 fb(-1) of data collected with the L3 detector at LEP at centre-of-mass energies root s = 183-209 GeV. Four final states are considered: q (q) over barv (v) over bar, q (q) over barl(+)l(-),l(+)l(-)l\u27(+)l\u27(-) and l(+)l(-)v (v) over bar, where l denotes either an electron or a muon. Their cross sections are measured and found to agree with the Standard Model predictions. In addition, the e(+)e(-) -\u3e Z gamma* -\u3e f (f) over barf\u27(f) over bar\u27 process is studied and its total cross section at the average centre-of-mass energy (root s) = 196.6 GeV is found to be 0.29 +/- 0.05 +/- 0.03 pb, where the first uncertainty is statistical and the second systematic, in agreement with the Standard Model prediction of 0.22 pb. Finally, the mass spectra of the q (q) over barl(+)l(-) final states are analysed to search for the possible production of a new neutral heavy particle, for which no evidence is found. (c) 2005 Published by Elsevier B.V

    Measurement of the Topological Branching Fractions of the τ\tau lepton at LEP

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    Using data collected with the L3 detector at LEP from 1992 to 1995 on the Z peak, we determine the branching fractions of the τ\tau lepton into one, three and five charged particles to be: \begin{eqnarray*} & {\cal{B}}(\tau\rightarrow (1-prong)) & = 85.274 \pm 0.105 \pm 0.073 \% , \\ & {\cal{B}}(\tau\rightarrow (3-prong)) & = 14.556 \pm 0.105 \pm 0.076 \%, \\ & {\cal{B}}(\tau\rightarrow (5-prong)) & = \phantom{0} 0.170 \pm 0.022 \pm 0.026 \%. \end{eqnarray*} \noindent The first uncertainties are statistical and the second systematic. The accuracy of these measurements alone is similar to that of the current world average.Using data collected with the L3 detector at LEP from 1992 to 1995 on the Z peak, we determine the branching fractions of the τ lepton into one, three and five charged particles to be: B (τ→( 1-prong ))=85.274±0.105±0.073%, B (τ→( 3-prong ))=14.556±0.105±0.076%, B (τ→( 5-prong ))=0.170±0.022±0.026%. The first uncertainties are statistical and the second systematic. The accuracy of these measurements alone is similar to that of the current world average.Using data collected with the L3 detector at LEP from 1992 to 1995 on the Z peak, we determine the branching fractions of the tau lepton into one, three and five charged particles to be: B(tau->(1-prong)) = 85.274 +- 0.105 +- 0.073 %, B(tau->(3-prong)) = 14.556 +- 0.105 +- 0.076 %, B(tau->(5-prong)) = 0.170 +- 0.022 +- 0.026 %. The first uncertainties are statistical and the second systematic. The accuracy of these measurements alone is similar to that of the current world average

    Search for Heavy Neutral and Charged Leptons in e+ee^+ e^- Annihilation at LEP

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    A search for exotic unstable neutral and charged heavy leptons as well as for stable charged heavy leptons is performed with the L3 detector at LEP. Sequential, vector and mirror natures of heavy leptons are considered. No evidence for their existence is found and lower limits on their masses are set.A search for exotic unstable neutral and charged heavy leptons as well as for stable charged heavy leptons is performed with the L3 detector at LEP. Sequential, vector and mirror natures of heavy leptons are considered. No evidence for their existence is found and lower limits on their masses are set

    Search for branons at LEP

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    We search, in the context of extra-dimension scenarios, for the possible existence of brane fluctuations, called branons. Events with a single photon or a single Z-boson and missing energy and momentum collected with the U detector in e(+)e(-) collisions at centre-of-mass energies root2 = 189-209 GeV are analysed. No excess over the Standard Model expectations is found and a lower limit at 95% confidence level of 103 GeV is derived for the mass of branons, for a scenario with small brane tensions. Alternatively, under the assumption of a light branon, brane tensions below 180 GeV are excluded. (C) 2004 Published by Elsevier B.V

    Search for Heavy Isosinglet Neutrino in e+ee^+ e^- Annihilation at LEP

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    We report on a search for the first generation heavy neutrino that is an isosinglet under the standard SU(2)LSU(2)_L gauge group. The data collected with the L3 detector at center-of-mass energies between 130~\hbox{\rm\ Ge\kern -0.1em V} and 208~\hbox{\rm\ Ge\kern -0.1em V} are used. The decay channel NeeW\mathrm{N}_\mathrm{e} \rightarrow \mathrm{e} \mathrm{W} is investigated and no evidence is found for a heavy neutrino, Ne\mathrm{N}_\mathrm{e}, in a mass range between 80~\hbox{\rm\ Ge\kern -0.1em V} and 205~\hbox{\rm\ Ge\kern -0.1em V}. Upper limits on the mixing parameter between the heavy and light neutrino are derived.We report on a search for the first generation heavy neutrino that is an isosinglet under the standard SU (2) L gauge group. The data collected with the L3 detector at center-of-mass energies between 130 GeV and 208 GeV are used. The decay channel N e →eW is investigated and no evidence is found for a heavy neutrino, N e , in a mass range between 80 GeV and 205 GeV. Upper limits on the mixing parameter between the heavy and light neutrino are derived.We report on a search for the first generation heavy neutrino that is an isosinglet under the standard SU(2)_L gauge group. The data collected with the L3 detector at center-of-mass energies between 130 GeV and 208 GeV are used.The decay channel N_e --> eW is investigated and no evidence is found for a heavy neutrino, N_e, in a mass range between 80 GeV and 205 GeV. Upper limits on the mixing parameter between the heavy and light neutrino are derived

    Compton scattering of quasi-real virtual photons at LEP

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    Compton scattering of quasi-real virtual photons, gamma e(+/-) -\u3e gamma e(+/-), is studied with 0.6 fb(-1) of data collected by the L3 detector at the LEP e(+)e(-) collider at centre-of-mass energies root s = 189-209 GeV. About 4500 events produced by the interaction of virtual photons emitted by e(+/-) of one beam with e(-/+) of the opposite beam are collected for effective centre-of-mass energies of the photon-electron and photon-positron systems in the range from root s\u27 = 35 GeV up to root s\u27 = 175 GeV, the highest energy at which Compton scattering was ever probed. The cross sections of the gamma e(+/-) -\u3e gamma e(+/-) process as a function of root s\u27 and of the rest-frame scattering angle are measured, combined with previous U measurements down to root s\u27 similar or equal to 20 GeV, and found to agree with the QED expectations. (c) 2005 Published by Elsevier B.V

    Search for an invisibly-decaying Higgs boson at LEP

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    A search for a Higgs boson produced in e(+)e(-) collisions in association with a Z boson and decaying into invisible particles is performed. Data collected at LEP with the U detector at centre-of-mass energies from 189 to 209 GeV are used, corresponding to an integrated luminosity of 0.63 fb(-1). Events with hadrons, electrons or muons with visible masses compatible with a Z boson and missing energy and momentum are selected. They are consistent with the Standard Model expectations. A lower limit of 112.3 GeV is set at 95% confidence level on the mass of the invisibly-decaying Higgs boson in the hypothesis that its production cross section equals that of the Standard Model Higgs boson. Relaxing this hypothesis, upper limits on the production cross section are derived. (C) 2005 Published by Elsevier B.V
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