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Träfflista för sökning "WFRF:(Hansen Thomas V. O.) "

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71.
  • Aad, G., et al. (författare)
  • Search for diphoton events with large missing transverse energy with 36 pb(-1) of 7 TeV proton-proton collision data with the ATLAS detector
  • 2011
  • Ingår i: European Physical Journal C. Particles and Fields. - : Springer. - 1434-6044 .- 1434-6052. ; 71:10
  • Tidskriftsartikel (refereegranskat)abstract
    • Making use of 36 pb(-1) of proton-proton collision data at root s = 7 TeV, the ATLAS Collaboration has performed a search for diphoton events with large missing transverse energy. Observing no excess of events above the Standard Model prediction, a 95% Confidence Level ( CL) upper limit is set on the cross section for new physics of sigma < 0.38-0.65 pb in the context of a generalised model of gauge-mediated supersymmetry breaking (GGM) with a bino-like lightest neutralino, and of sigma < 0.18-0.23 pb in the context of a specific model with one universal extra dimension (UED). A 95% CL lower limit of 560 GeV, for bino masses above 50 GeV, is set on the GGM gluino mass, while a lower limit of 1/R > 961 GeV is set on the UED compactification radius R. These limits provide the most stringent tests of these models to date.
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72.
  • Aad, G., et al. (författare)
  • Search for Down-Type Fourth Generation Quarks with the ATLAS Detector in Events with One Lepton and Hadronically Decaying W Bosons
  • 2012
  • Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114 .- 0031-9007. ; 109:3
  • Tidskriftsartikel (refereegranskat)abstract
    • This Letter presents a search for pair production of heavy down-type quarks decaying via b' -> Wt in the lepton + jets channel, as b'(b) over bar' -> W(-)tW(+)(t) over bar -> b (b) over barW(+)W(-)W(+)W- -> l(+/-) nu b (b) over barq (q) over barq (q) over barq ($) over barq. In addition to requiring exactly one lepton, large missing transverse momentum, and at least six jets, the invariant mass of nearby jet pairs is used to identify high transverse momentum W bosons. In data corresponding to an integrated luminosity of 1.04 fb(-1) from pp collisions at root s = 7 TeV recorded with the ATLAS detector, a heavy down-type quark with mass less than 480 GeV can be excluded at the 95% confidence level.
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73.
  • Aad, G., et al. (författare)
  • Search for excited leptons in proton-proton collisions at root s=7 TeV with the ATLAS detector
  • 2012
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - : American Physical Society. - 1550-2368 .- 1550-7998. ; 85:7
  • Tidskriftsartikel (refereegranskat)abstract
    • The ATLAS detector is used to search for excited leptons in the electromagnetic radiative decay channel l* -> l gamma. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 2.05 fb(-1). No evidence for excited leptons is found, and limits are set on the compositeness scale Lambda as a function of the excited lepton mass m(l*). In the special case where Lambda = m(l*), excited electron and muon masses below 1.87 TeV and 1.75 TeV are excluded at 95% C.L., respectively.
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74.
  • Aad, G., et al. (författare)
  • Search for heavy long-lived charged particles with the ATLAS detector in pp collisions at root s=7 TeV
  • 2011
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier. - 0370-2693 .- 1873-2445. ; 703:4, s. 428-446
  • Tidskriftsartikel (refereegranskat)abstract
    • A search for long-lived charged particles reaching the muon spectrometer is performed using a data sample of 37 pb(-1) from pp collisions at root s = 7 TeV collected by the ATLAS detector at the LHC in 2010. No excess is observed above the estimated background. Stable (tau) over bar sleptons are excluded at 95% CL up to a mass of 136 GeV, in GMSB models with N-5 = 3 , m(messenger) = 250 TeV, sign(mu) = 1 and tan beta = 5. Electroweak production of sleptons is excluded up to a mass of 110 GeV. Gluino R-hadrons in a generic interaction model are excluded up to masses of 530 GeV to 544 GeV depending on the fraction of R-hadrons produced as (g) over bar -balls. (C) 2011 CERN. Published by Elsevier By. All rights reserved.
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75.
  • Aad, G., et al. (författare)
  • Search for massive long-lived highly ionising particles with the ATLAS detector at the LHC
  • 2011
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier. - 0370-2693 .- 1873-2445. ; 698:5, s. 353-370
  • Tidskriftsartikel (refereegranskat)abstract
    • A search is made for massive highly ionising particles with lifetimes in excess of 100 ns, with the ATLAS experiment at the Large Hadron Collider, using 3.1 pb(-1) of pp collision data taken at root s = 7 TeV. The signature of energy loss in the ATLAS inner detector and electromagnetic calorimeter is used. No such particles are found and limits on the production cross section for electric charges 6e <= vertical bar q vertical bar <= 17e and masses 200 GeV <= m <= 1000 GeV are set in the range 1-12 pb for different hypotheses on the production mechanism. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.
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76.
  • Aad, G., et al. (författare)
  • Search for pair-produced heavy quarks decaying to Wq in the two-lepton channel at root(s)=7 TeV with the ATLAS detector
  • 2012
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - : American Physical Society. - 1550-2368 .- 1550-7998. ; 86:1
  • Tidskriftsartikel (refereegranskat)abstract
    • A search is presented for heavy-quark pair production (Q (Q) over bar) under the decay hypothesis Q (Q) over bar -> W(+)qW(-)(q) over bar with q = d, s, b for up-type Q or q = u, c for down-type Q. The search is performed with 1.04 fb(-1) of integrated luminosity from pp collisions at root s = 7 TeV collected by the ATLAS detector at the CERN LHC. Dilepton final states are selected, requiring large missing transverse momentum and at least two jets. Mass reconstruction of heavy-quark candidates is performed by assuming that the W boson decay products are nearly collinear. The data are in agreement with standard model expectations; a heavy quark with mass less than 350 GeV is excluded at 95% confidence level.
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77.
  • Aad, G., et al. (författare)
  • Search for tb Resonances in Proton-Proton Collisions at root s=7 TeV with the ATLAS Detector
  • 2012
  • Ingår i: Physical Review Letters. - : American Physical Society. - 1079-7114 .- 0031-9007. ; 109:8
  • Tidskriftsartikel (refereegranskat)abstract
    • This Letter presents a search for tb resonances in 1.04 fb(-1) of LHC proton-proton collision data collected by the ATLAS detector at a center-of-mass energy of 7 TeV. Events with a lepton, missing transverse momentum, and two jets are selected and the invariant mass of the corresponding final state is reconstructed. The search exploits the shape of the tb invariant mass distribution compared to the expected standard model backgrounds. The model of a right-handed W'(R) with standard model-like couplings is chosen as the benchmark model for this search. No statistically significant excess of events is observed in the data, and upper limits on the cross section times the branching ratio of W'(R) resonances at 95% C.L. lie in the range of 6.1-1.0 pb for W'(R) masses ranging from 0.5 to 2.0 TeV. These limits are translated into a lower bound on the allowed right-handed W'(R) mass, giving mW'(R) > 1.13 TeV at 95% C.L.
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78.
  • Aad, G., et al. (författare)
  • Study of jet shapes in inclusive jet production in pp collisions at root s=7 TeV using the ATLAS detector
  • 2011
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - : American Physical Society. - 1550-2368 .- 1550-7998. ; 83:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Jet shapes have been measured in inclusive jet production in proton-proton collisions at root s = 7 TeV using 3 pb(-1) of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-k(t) algorithm with transverse momentum 30 GeV < p(T) < 600 GeV and rapidity in the region vertical bar y vertical bar < 2.8. The data are corrected for detector effects and compared to several leading-order QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measured jets become narrower with increasing jet transverse momentum and the jet shapes present a moderate jet rapidity dependence. Within QCD, the data test a variety of perturbative and nonperturbative effects. In particular, the data show sensitivity to the details of the parton shower, fragmentation, and underlying event models in the Monte Carlo generators. For an appropriate choice of the parameters used in these models, the data are well described.
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79.
  • Aad, G., et al. (författare)
  • A measurement of the ratio of the W and Z cross sections with exactly one associated jet in pp collisions at root s=7 TeV with ATLAS
  • 2012
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier. - 0370-2693 .- 1873-2445. ; 708:3-5, s. 221-240
  • Tidskriftsartikel (refereegranskat)abstract
    • The ratio of production cross sections of the W and Z bosons with exactly one associated jet is presented as a function of jet transverse momentum threshold. The measurement has been designed to maximise cancellation of experimental and theoretical uncertainties, and is reported both within a particle-level kinematic range corresponding to the detector acceptance and as a total cross-section ratio. Results are obtained with the ATLAS detector at the LHC in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 33 pb(-1). The results are compared with perturbative leading-order, leading-log, and next-to-leading-order QCD predictions, and are found to agree within experimental and theoretical uncertainties. The ratio is measured for events with a single jet with p(T) > 30 GeV to be 8.73 +/- 0.30(stat) +/- 0.40(syst) in the electron channel, and 8.49 +/- 0.23(stat) +/- 0.33(syst) in the muon channel. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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80.
  • Aad, G., et al. (författare)
  • Charged-particle multiplicities in pp interactions measured with the ATLAS detector at the LHC
  • 2011
  • Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 13
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements are presented from proton-proton collisions at centre-of-mass energies of root s = 0.9, 2.36 and 7 TeV recorded with the ATLAS detector at the LHC. Events were collected using a single-arm minimum-bias trigger. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the relationship between the mean transverse momentum and charged-particle multiplicity are measured. Measurements in different regions of phase space are shown, providing diffraction-reduced measurements as well as more inclusive ones. The observed distributions are corrected to well-defined phase-space regions, using model-independent corrections. The results are compared to each other and to various Monte Carlo (MC) models, including a new AMBT1 pythia6 tune. In all the kinematic regions considered, the particle multiplicities are higher than predicted by the MC models. The central charged-particle multiplicity per event and unit of pseudorapidity, for tracks with p(T) > 100 MeV, is measured to be 3.483 +/- 0.009 (stat) +/- 0.106 (syst) at root s = 0.9 TeV and 5.630 +/- 0.003 (stat) +/- 0.169 (syst) at root s = 7 TeV.
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