1,524 research outputs found

    Position resolution and particle identification with the ATLAS EM calorimeter

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    In the years between 2000 and 2002 several pre-series and series modules of the ATLAS EM barrel and end-cap calorimeter were exposed to electron, photon and pion beams. The performance of the calorimeter with respect to its finely segmented first sampling has been studied. The polar angle resolution has been found to be in the range 50-60 mrad/sqrt(E (GeV)). The neutral pion rejection has been measured to be about 3.5 for 90% photon selection efficiency at pT=50 GeV/c. Electron-pion separation studies have indicated that a pion fake rate of (0.07-0.5)% can be achieved while maintaining 90% electron identification efficiency for energies up to 40 GeV.Comment: 32 pages, 22 figures, to be published in NIM

    Energy Linearity and Resolution of the ATLAS Electromagnetic Barrel Calorimeter in an Electron Test-Beam

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    A module of the ATLAS electromagnetic barrel liquid argon calorimeter was exposed to the CERN electron test-beam at the H8 beam line upgraded for precision momentum measurement. The available energies of the electron beam ranged from 10 to 245 GeV. The electron beam impinged at one point corresponding to a pseudo-rapidity of eta=0.687 and an azimuthal angle of phi=0.28 in the ATLAS coordinate system. A detailed study of several effects biasing the electron energy measurement allowed an energy reconstruction procedure to be developed that ensures a good linearity and a good resolution. Use is made of detailed Monte Carlo simulations based on Geant which describe the longitudinal and transverse shower profiles as well as the energy distributions. For electron energies between 15 GeV and 180 GeV the deviation of the measured incident electron energy over the beam energy is within 0.1%. The systematic uncertainty of the measurement is about 0.1% at low energies and negligible at high energies. The energy resolution is found to be about 10% sqrt(E) for the sampling term and about 0.2% for the local constant term

    Search for Anomalous Couplings in the Higgs Sector at LEP

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    Anomalous couplings of the Higgs boson are searched for through the processes e^+ e^- -> H gamma, e^+ e^- -> e^+ e^- H and e^+ e^- -> HZ. The mass range 70 GeV < m_H < 190 GeV is explored using 602 pb^-1 of integrated luminosity collected with the L3 detector at LEP at centre-of-mass energies sqrt(s)=189-209 GeV. The Higgs decay channels H -> ffbar, H -> gamma gamma, H -> Z\gamma and H -> WW^(*) are considered and no evidence is found for anomalous Higgs production or decay. Limits on the anomalous couplings d, db, Delta(g1z), Delta(kappa_gamma) and xi^2 are derived as well as limits on the H -> gamma gamma and H -> Z gamma decay rates

    Measurement of the Cross Section of W-boson pair production at LEP

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    The cross section of W-boson pair-production is measured with the L3 detector at LEP. In a data sample corresponding to a total luminosity of 629.4/pb, collected at centre-of-mass energies ranging from 189 to 209 GeV, 9834 four-fermion events with W bosons decaying into hadrons or leptons are selected. The total cross section is measured with a precision of 1.4 % and agrees with the Standard Model expectation. Assuming charged-lepton universality, the branching fraction for hadronic W-boson decays is measured to be: Br(W-->hadrons) = 67.50 +- 0.42 (stat.) +- 0.30(syst.) %, in agreement with the Standard Model. Differential cross sections as a function of the W- production angle are also measured for the semi-leptonic channels qqev and qqmv

    Search for Doubly-Charged Higgs Bosons at LEP

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    Doubly-charged Higgs bosons are searched for in e^+e^- collision data collected with the L3 detector at LEP at centre-of-mass energies up to 209 GeV. Final states with four leptons are analysed to tag the pair-production of doubly charged Higgs bosons. No significant excess is found and lower limits at 95% confidence level on the doubly-charged Higgs boson mass are derived. They vary from 95.5 GeV to 100.2 GeV, depending on the decay mode. Doubly-charged Higgs bosons which couple to electrons would modify the cross section and forward-backward asymmetry of the e^+e^- -> e^+e^- process. The measurements of these quantities do not deviate from the Standard Model expectations and doubly-charged Higgs bosons with masses up to the order of a TeV are excluded

    Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector