| 1. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports A Review Section of Physics Letters. - Elsevier Science B.V.. - 0370-1573. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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| 2. |
- Åsman, Barbro, et al.
(författare)
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Measurement of inclusive jet and dijet cross sections in proton-proton collisions at 7 TeV centre-of-mass energy with the ATLAS detector
- 2011
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Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 71:2
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Tidskriftsartikel (refereegranskat)abstract
- Jet cross sections have been measured for the first time in proton-proton collisions at a centre-of-mass energy of 7 TeV using the ATLAS detector. The measurement uses an integrated luminosity of 17 nb(-1) recorded at the Large Hadron Collider. The anti-k(t) algorithm is used to identify jets, with two jet resolution parameters, R = 0.4 and 0.6. The dominant uncertainty comes from the jet energy scale, which is determined to within 7% for central jets above 60 GeV transverse momentum. Inclusive single-jet differential cross sections are presented as functions of jet transverse momentum and rapidity. Dijet cross sections are presented as functions of dijet mass and the angular variable chi. The results are compared to expectations based on next-to-leading-order QCD, which agree with the data, providing a validation of the theory in a new kinematic regime.
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| 3. |
- Aad, G., et al.
(författare)
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Measurement of the cross-section for b-jets produced in association with a Z boson at root s=7 TeV with the ATLAS detector ATLAS Collaboration
- 2012
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Ingår i: Physics Letters B. - Elsevier Science BV. - 0370-2693. ; 706:4-5, s. 295-313
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Tidskriftsartikel (refereegranskat)abstract
- A measurement is presented of the inclusive cross-section for b-jet production in association with a Z boson in pp collisions at a centre-of-mass energy of root s = 7 TeV. The analysis uses the data sample collected by the ATLAS experiment in 2010, corresponding to an integrated luminosity of approximately 36 pb(-1). The event selection requires a Z boson decaying into high P-T electrons or muons, and at least one b-jet, identified by its displaced vertex, with transverse momentum p(T) > 25 GeV and rapidity vertical bar y vertical bar < 2.1. After subtraction of background processes, the yield is extracted from the vertex mass distribution of the candidate b-jets. The ratio of this cross-section to the inclusive Z cross-section (the average number of b-jets per Z event) is also measured. Both results are found to be in good agreement with perturbative QCD predictions at next-to-leading order. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.
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| 4. |
- Aad, G., et al.
(författare)
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Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at root s=7 TeV with the ATLAS detector
- 2011
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Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 71:12
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Tidskriftsartikel (refereegranskat)abstract
- The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV, using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb(-1). The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 < p(T) < 400 GeV and rapidity in the range vertical bar y vertical bar < 2.1. The b<(b)over bar>-dijet cross-section is measured as a function of the dijet invariant mass in the range 110 < m(jj) < 760 GeV, the azimuthal angle difference between the two jets and the angular variable chi in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured b (b) over bar -dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.
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| 5. |
- Aad, G., et al.
(författare)
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Measurement of the jet fragmentation function and transverse profile in proton-proton collisions at a center-of-mass energy of 7 TeV with the ATLAS detector
- 2011
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Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 71:11
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Tidskriftsartikel (refereegranskat)abstract
- The jet fragmentation function and transverse profile for jets with 25 GeV < p(Tjet) < 500 GeV and |eta(jet)| < 1.2 produced in proton-proton collisions with a center-of-mass energy of 7 TeV are presented. The measurement is performed using data with an integrated luminosity of 36 pb(-1). Jets are reconstructed and their momentum measured using calorimetric information. The momenta of the charged particle constituents are measured using the tracking system. The distributions corrected for detector effects are compared with various Monte Carlo event generators and generator tunes. Several of these choices show good agreement with the measured fragmentation function. None of these choices reproduce both the transverse profile and fragmentation function over the full kinematic range of the measurement.
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| 6. |
- Aad, G, et al.
(författare)
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Search for a heavy gauge boson decaying to a charged lepton and a neutrino in 1 fb(-1) of pp collisions at root s=7 TeV using the ATLAS detector ATLAS Collaboration
- 2011
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Ingår i: Physics Letters B. - Elsevier Science BV. - 0370-2693. ; 705:1-2, s. 28-46
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Tidskriftsartikel (refereegranskat)abstract
- The ATLAS detector at the LHC is used to search for high-mass states, such as heavy charged gauge bosons (W '), decaying to a charged lepton (electron or muon) and a neutrino. 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 1.04 fb(-1). No excess above Standard Model expectations is observed. A W ' with Sequential Standard Model couplings is excluded at the 95% confidence level for masses up to 2.15 TeV. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.
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| 7. |
- Aad, G., et al.
(författare)
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Search for a heavy neutral particle decaying into an electron and a muon using 1 fb(-1) of ATLAS data
- 2011
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Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 71:12
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Tidskriftsartikel (refereegranskat)abstract
- A search is presented for a high mass neutral particle that decays directly to the e(+/-) mu(-/+) final state. The data sample was recorded by the ATLAS detector in root s = 7 TeV pp collisions at the LHC from March to June 2011 and corresponds to an integrated luminosity of 1.07 fb(-1). The data are found to be consistent with the Standard Model background. The high e(+/-) mu(-/+) mass region is used to set 95% confidence level upper limits on the production of two possible new physics processes: tau sneutrinos in an R-parity violating supersymmetric model and Z'-like vector bosons in a lepton flavor violating model.
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| 8. |
- Aad, G., et al.
(författare)
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Search for a Standard Model Higgs Boson in the H -> ZZ -> l(+)l(-)v(v)over-bar Decay Channel with the ATLAS Detector
- 2011
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Ingår i: Physical Review Letters. - Amer Physical Soc. - 0031-9007. ; 107:22
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Tidskriftsartikel (refereegranskat)abstract
- A search for a heavy standard model Higgs boson decaying via H -> ZZ -> l(+)l(-)v (v) over bar, where l = e, mu, is presented. It is based on proton-proton collision data at root s = 7 TeV, collected by the ATLAS experiment at the LHC in the first half of 2011 and corresponding to an integrated luminosity of 1.04 fb(-1). The data are compared to the expected standard model backgrounds. The data and the background expectations are found to be in agreement and upper limits are placed on the Higgs boson production cross section over the entire mass window considered; in particular, the production of a standard model Higgs boson is excluded in the region 340 < m(H) < 450 GeV at the 95% confidence level.
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| 9. |
- Aad, G., et al.
(författare)
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Search for diphoton events with large missing transverse momentum in 1 fb(-1) of 7 TeV proton-proton collision data with the ATLAS detector ATLAS Collaboration
- 2012
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Ingår i: Physics Letters B. - Elsevier Science Bv. - 0370-2693. ; 710:4-5, s. 519-537
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Tidskriftsartikel (refereegranskat)abstract
- A search for diphoton events with large missing transverse momentum has been performed using 1.07 fb(-1) of proton-proton collision data at root s = 7 TeV recorded with the ATLAS detector. No excess of events was observed above the Standard Model prediction and 95% Confidence Level (CL) upper limits are set on the production cross section for new physics. The limits depend on each model parameter space and vary as follows: sigma < (22-129) fb in the context of a generalised model of gauge-mediated supersymmetry breaking (GGM) with a bino-like lightest neutralino, sigma < (27-91) fb in the context of a minimal model of gauge-mediated supersymmetry breaking (SPS8), and sigma < (15-27) fb in the context of a specific model with one universal extra dimension (UED). A 95% CL lower limit of 805 GeV, for bino masses above 50 GeV, is set on the GGM gluino mass. Lower limits of 145 TeV and 1.23 TeV are set on the SPS8 breaking scale Lambda and on the UED compactification scale 1/R, respectively. These limits provide the most stringent tests of these models to date. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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| 10. |
- Aad, G., et al.
(författare)
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Search for strong gravity signatures in same-sign dimuon final states using the ATLAS detector at the LHC
- 2012
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Ingår i: Physics Letters B. - Elsevier Science Bv. - 0370-2693. ; 709:4-5, s. 322-340
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Tidskriftsartikel (refereegranskat)abstract
- A search for microscopic black holes has been performed in a same-sign dimuon final state using 1.3 fb(-1) of proton-proton collision data collected with the ATLAS detector at a centre of mass energy of 7 TeV at the CERN Large Hadron Collider. The data are found to be consistent with the expectation from the Standard Model and the results are used to derive exclusion contours in the context of a low scale gravity model. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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