24 research outputs found

    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

    Search for scalar leptons and scalar quarks at LEP

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    Scalar partners of quarks and leptons, predicted in supersymmetric models, are searched for in e(+)e(-) collisions at centre-of-mass energies between 192 and 209 GeV at LEP. No evidence for any such particle is found in a data sample of 450 pb(-1). Upper limits on their production cross sections are set and lower limits on their masses are derived in the framework of the Minimal Supersymmetric Standard Model. (C) 2003 Published by Elsevier B.V

    Inclusive charged hadron production in two-photon collisions at LEP

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    Inclusive charged hadron production, e(+)e(-) --\u3e 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, p(t), and pseudo-rapidity, eta. For p(1) less than or equal to 1.5 GeV, the data are well described by an exponential, typical of soft hadronic processes. For higher p(1), the onset of perturbative QCD processes is observed. The pi(+/-) production cross section for p(t) \u3e 5 GeV is much higher than the NLO QCD predictions. (C) 2003 Elsevier Science B.V. All rights reserved

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

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    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 e+eZe+ee^{+}e^{-}\to Ze^{+}e^{-} Process at LEP

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    The cross section of the process e+eZe+e\rm e^+e^-\rightarrow Ze^+e^- is measured with ~0.7\,fb1^{-1} of data collected with the L3 detector at LEP. Decays of the Z boson into quarks and muons are considered at centre-of-mass energies ranging from 183183 GeV up to 209209 GeV. The measurements are found to agree with Standard Model predictions, achieving a precision of about 10\% for the hadronic channel.The cross section of the process e + e − →Ze + e − is measured with  0.7 fb −1 of data collected with the L3 detector at LEP. Decays of the Z boson into quarks and muons are considered at centre-of-mass energies ranging from 183 GeV up to 209 GeV . The measurements are found to agree with Standard Model predictions, achieving a precision of about 10% for the hadronic channel.The cross section of the process e+e- -> Ze+e is measured with 0.7fb^-1 of data collected with the L3 detector at LEP. Decays of the Z boson into quarks and muons are considered at centre-of-mass energies ranging from 183GeV up to 209GeV. The measurements are found to agree with Standard Model predictions, achieving a precision of about 10% for the hadronic channel

    Z boson pair-production at LEP

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    Events stemming from the pair-production of Z bosons in e(+)e(-) collisions are studied using 217.4 pb(-1) of data collected with the L3 detector at Centre-of-mass energies from 200 GeV up to 209 GeV The special case of events with b quarks is also investigated. Combining these events with those collected at lower centre-of-mass energies, the Standard Model predictions for the production mechanism are verified. In addition, limits are set on anomalous couplings of neutral gauge bosons and on effects of extra space dimensions

    Study of hadronic event shape in flavour tagged events in e+e- annihilation at s\sqrt{s}= 197 GeV

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    Results are presented from a study of the structure of hadronic events in highenergy (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 avour 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 avours 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.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

    Search for charged Higg bosons at LEP

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    A search for pair-produced charged Higgs bosons is performed with the L3 detector at LEP using data collected at centre-of-mass energies between 189 and 209 GeV, corresponding to an integrated luminosity of 629.4 pb(-1). Decays into a charm and a strange quark or into a tau lepton and its neutrino are considered. No significant excess is observed and lower limits on the mass of the charged Higgs boson are derived at the 95% confidence level. They vary from 76.5 to 82.7 GeV, as a function of the H+/- --\u3e taunu branching ratio. (C) 2003 Published by Elsevier B.V

    Measurement of charged-particle multiplicity distributions and their H-q moments in hadronic Z decays at LEP

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    The charged-particle multiplicity distribution is measured for all hadronic events as well as for light-quark and b-quark events produced in e(+)e(-) collisions at the Z pole. Moments of the charged-particle multiplicity distributions are calculated. The H-q moments of the multiplicity distributions are studied, and their quasi-oscillations as a function of the rank of the moment are investigated. (C) 2003 Published by Elsevier B.V
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