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Träfflista för sökning "WFRF:(Jon And K.) srt2:(2010-2014)"

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1.
  • Aad, G., et al. (författare)
  • Search for Quantum Black Hole Production in High-Invariant-Mass Lepton plus Jet Final States Using pp Collisions at root s=8 TeV and the ATLAS Detector
  • 2014
  • Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114 .- 0031-9007. ; 112:9
  • Tidskriftsartikel (refereegranskat)abstract
    • This Letter presents a search for quantum black-hole production using 20.3 fb(-1) of data collected with the ATLAS detector in pp collisions at the LHC at root s = 8 TeV. The quantum black holes are assumed to decay into a final state characterized by a lepton (electron or muon) and a jet. In either channel, no event with a lepton-jet invariant mass of 3.5 TeV or more is observed, consistent with the expected background. Limits are set on the product of cross sections and branching fractions for the lepton + jet final states of quantum black holes produced in a search region for invariant masses above 1 TeV. The combined 95% confidence level upper limit on this product for quantum black holes with threshold mass above 3.5 TeV is 0.18 fb. This limit constrains the threshold quantum black-hole mass to be above 5.3 TeV in the model considered.
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2.
  • Aad, G., et al. (författare)
  • Measurement of chi(c1) and chi(c2) production with root s=7 TeV pp collisions at ATLAS
  • 2014
  • Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; :7
  • Tidskriftsartikel (refereegranskat)abstract
    • The prompt and non-prompt production cross-sections for the chi(c1) and chi(c2) charmonium states are measured in pp collisions at root s = 7TeV with the ATLAS detector at the LHC using 4.5 fb(-1) of integrated luminosity. The chi(c) states are reconstructed through the radiative decay chi c -> J/psi gamma ( with J/psi -> mu(+)mu(-)) where photons are reconstructed from gamma -> e(+)e(-) conversions. The production rate of the chi(c2) state relative to the chi(c1) state is measured for prompt and non-prompt chi(c) as a function of J/psi transverse momentum. The prompt chi(c) cross-sections are combined with existing measurements of prompt J/psi production to derive the fraction of prompt J/psi produced in feed-down from chi(c) decays. The fractions of chi(c1) and chi(c2) produced in b-hadron decays are also measured.
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3.
  • Aad, G., et al. (författare)
  • Measurement of dijet cross-sections in pp collisions at 7 TeV centre-of-mass energy using the ATLAS detector
  • 2014
  • Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; :5
  • Tidskriftsartikel (refereegranskat)abstract
    • Double-differential dijet cross-sections measured in pp collisions at the LHC with a 7 TeV centre-of-mass energy are presented as functions of dijet mass and half the rapidity separation of the two highest-p(T) jets. These measurements are obtained using data corresponding to an integrated luminosity of 4.5 fb(-1), recorded by the ATLAS detector in 2011. The data are corrected for detector effects so that cross-sections are presented at the particle level. Cross-sections are measured up to 5 TeV dijet mass using jets reconstructed with the anti-k(t) algorithm for values of the jet radius parameter of 0.4 and 0.6. The cross-sections are compared with next-to-leading-order perturbative QCD calculations by NLOJet++ corrected to account for non-perturbative effects. Comparisons with POWHEG predictions, using a next-to-leading-order matrix element calculation interfaced to a parton-shower Monte Carlo simulation, are also shown. Electroweak effects are accounted for in both cases. The quantitative comparison of data and theoretical predictions obtained using various parameterizations of the parton distribution functions is performed using a frequentist method. In general, good agreement with data is observed for the NLOJet++ theoretical predictions when using the CT10, NNPDF2.1 and MSTW 2008 PDF sets. Disagreement is observed when using the ABM11 and HERAPDF1.5 PDF sets for some ranges of dijet mass and half the rapidity separation. An example setting a lower limit on the compositeness scale for a model of contact interactions is presented, showing that the unfolded results can be used to constrain contributions to dijet production beyond that predicted by the Standard Model.
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4.
  • Aad, G., et al. (författare)
  • Measurement of the mass difference between top and anti-top quarks in pp collisions at root s=7 TeV using the ATLAS detector
  • 2014
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier. - 0370-2693 .- 1873-2445. ; 728, s. 363-379
  • Tidskriftsartikel (refereegranskat)abstract
    • A measurement of the mass difference between top and anti-top quarks is presented. In a 4.7 fb(-1) data sample of proton-proton collisions at root s = 7 TeV recorded with the ATLAS detector at the LHC, events consistent with t (t) over bar production and decay into a single charged lepton final state are reconstructed. For each event, the mass difference between the top and anti-top quark candidate is calculated. A two b-tag requirement is used in order to reduce the background contribution. A maximum likelihood fit to these per-event mass differences yields Delta m = m(t) - m((t) over bar) = 0.67 +/- 0.61 (stat) +/- 0.41 (syst) GeV, consistent with CPT invariance. (C) 2013 The Authors. Published by Elsevier B.V. All rights reserved.
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5.
  • Aad, G., et al. (författare)
  • Search for a multi-Higgs-boson cascade in W(+)W(-)b(b)over-bar events with the ATLAS detector in pp collisions at root s=8 TeV
  • 2014
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - : American Physical Society. - 1550-2368 .- 1550-7998. ; 89:3
  • Tidskriftsartikel (refereegranskat)abstract
    • A search is presented for new particles in an extension to the Standard Model that includes a heavy Higgs boson (H-0), an intermediate charged Higgs-boson pair (H-+/-), and a light Higgs boson (h(0)). The analysis searches for events involving the production of a single heavy neutral Higgs boson which decays to the charged Higgs boson and a W boson, where the charged Higgs boson subsequently decays into a W boson and the lightest neutral Higgs boson decaying to a bottom-antibottom-quark pair. Such a cascade results in a W-boson pair and a bottom-antibottom-quark pair in the final state. Events with exactly one lepton, missing transverse momentum, and at least four jets are selected from a data sample corresponding to an integrated luminosity of 20.3 fb(-1), collected by the ATLAS detector in proton-proton collisions at root s = 8 TeV at the LHC. The data are found to be consistent with Standard Model predictions, and 95% confidence-level upper limits are set on the product of cross section and branching ratio. These limits range from 0.065 to 43 pb as a function of H-0 and H-+/- masses, with m(h)o fixed at 125 GeV.
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6.
  • Aad, G., et al. (författare)
  • Search for Invisible Decays of a Higgs Boson Produced in Association with a Z Boson in ATLAS
  • 2014
  • Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114 .- 0031-9007. ; 112:20
  • Tidskriftsartikel (refereegranskat)abstract
    • A search for evidence of invisible-particle decay modes of a Higgs boson produced in association with a Z boson at the Large Hadron Collider is presented. No deviation from the standard model expectation is observed in 4.5 fb(-1) (20.3 fb(-1)) of 7 (8) TeV pp collision data collected by the ATLAS experiment. Assuming the standard model rate for ZH production, an upper limit of 75%, at the 95% confidence level is set on the branching ratio to invisible-particle decay modes of the Higgs boson at a mass of 125.5 GeV. The limit on the branching ratio is also interpreted in terms of an upper limit on the allowed dark matter-nucleon scattering cross section within a Higgs-portal dark matter scenario. Within the constraints of such a scenario, the results presented in this Letter provide the strongest available limits for low-mass dark matter candidates. Limits are also set on an additional neutral Higgs boson, in the mass range 110 < m(H) < 400 GeV, produced in association with a Z boson and decaying to invisible particles.
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7.
  • Aad, G., et al. (författare)
  • Standalone vertex finding in the ATLAS muon spectrometer
  • 2014
  • Ingår i: Journal of Instrumentation. - : IOP Publishing. - 1748-0221. ; 9
  • Tidskriftsartikel (refereegranskat)abstract
    • A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to b (b) over bar final states, and pp collision data at root s = 7 TeV collected with the ATLAS detector at the LHC during 2011.
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8.
  • Aad, G., et al. (författare)
  • Measurement of the electroweak production of dijets in association with a Z-boson and distributions sensitive to vector boson fusion in proton-proton collisions at=8 TeV using the ATLAS detector
  • 2014
  • Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; :4
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements of fiducial cross sections for the electroweak production of two jets in association with a Z-boson are presented. The measurements are performed using 20.3 fb(-1) of proton-proton collision data collected at a centre-of-mass energy of = 8 TeV by the ATLAS experiment at the Large Hadron Collider. The electroweak component is extracted by a fit to the dijet invariant mass distribution in a fiducial region chosen to enhance the electroweak contribution over the dominant background in which the jets are produced via the strong interaction. The electroweak cross sections measured in two fiducial regions are in good agreement with the Standard Model expectations and the background-only hypothesis is rejected with significance above the 5 sigma level. The electroweak process includes the vector boson fusion production of a Z-boson and the data are used to place limits on anomalous triple gauge boson couplings. In addition, measurements of cross sections and differential distributions for inclusive Z-boson-plus-dijet production are performed in five fiducial regions, each with different sensitivity to the electroweak contribution. The results are corrected for detector effects and compared to predictions from the Sherpa and Powheg event generators.
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9.
  • Aad, G., et al. (författare)
  • Measurement of the low-mass Drell-Yan differential cross section at root s=7 TeV using the ATLAS detector
  • 2014
  • Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; :6
  • Tidskriftsartikel (refereegranskat)abstract
    • The differential cross section for the process Z/gamma* -> ll (l = e, mu) as a function of dilepton invariant mass is measured in pp collisions at root s = 7 TeV at the LHC using the ATLAS detector. The measurement is performed in the e and mu channels for invariant masses between 26 GeV and 66 GeV using an integrated luminosity of 1.6 fb(-1) collected in 2011 and these measurements are combined. The analysis is extended to invariant masses as low as 12 GeV in the muon channel using 35 pb(-1) of data collected in 2010. The cross sections are determined within fiducial acceptance regions and corrections to extrapolate the measurements to the full kinematic range are provided. Next-to-next-to-leading-order QCD predictions provide a significantly better description of the results than next-to-leading-order QCD calculations, unless the latter are matched to a parton shower calculation.
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10.
  • Aad, G., et al. (författare)
  • Measurements of normalized differential cross sections for t(t)over-bar production in pp collisions at root(s)=7 TeV using the ATLAS detector
  • 2014
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - : American Physical Society. - 1550-2368 .- 1550-7998. ; 90:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements of normalized differential cross sections for top-quark pair production are presented as a function of the top-quark transverse momentum, and of the mass, transverse momentum, and rapidity of the t (t) over bar system, in proton proton collisions at a center-of-mass energy of root s = 7 TeV. The data set corresponds to an integrated luminosity of 4.6 fb(-1), recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton jets channel, requiring exactly one lepton and at least four jets with at least one of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector efficiency and resolution effects and are compared to several Monte Carlo simulations and theory calculations. The results are in fair agreement with the predictions in a wide kinematic range. Nevertheless, data distributions are softer than predicted for higher values of the mass of the t (t) over bar system and of the top-quark transverse momentum. The measurements can also discriminate among different sets of parton distribution functions.
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