| 1. |
- Aad, G., et al.
(författare)
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Measurement of the W(+/-)Z production cross section and limits on anomalous triple gauge couplings in proton-proton collisions at root s=7 TeV with the ATLAS detector
- 2012
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Ingår i: Physics Letters B. - Elsevier Science Bv. - 0370-2693. ; 709:4-5, s. 341-357
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Tidskriftsartikel (refereegranskat)abstract
- This Letter presents a measurement of W(+/-)Z production in 1.02 fb(-1) of pp collision data at root s = 7 TeV collected by the ATLAS experiment in 2011. Doubly leptonic decay events are selected with electrons, muons and missing transverse momentum in the final state. In total 71 candidates are observed, with a background expectation of 12.1 +/- 1.4(stat.)(-2.0)(+4.1)(syst.) events. The total cross section for W(+/-)Z production for Z/gamma* masses within the range 66 GeV to 116 GeV is determined to be sigma(tot)(WZ) = 20.5(-2.8)(+3.1)(stat.)(-1.3)(+1.4)(syst)(-0.8)(+0.9)(lumi.) pb, which is consistent with the Standard Model expectation of 17.3(0.8)(+1.3) pb. Limits on anomalous triple gauge boson couplings are extracted. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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| 2. |
- Aad, G., et al.
(författare)
-
Measurement of inclusive jet and dijet production in pp collisions at root s=7 TeV using the ATLAS detector
- 2012
-
Ingår i: Physical Review D. - American Physical Society. - 1550-7998. ; 86:1, s. 014022
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive jet and dijet cross sections have been measured in proton-proton collisions at a center-of-mass energy of 7 TeV using the ATLAS detector at the Large Hadron Collider. The cross sections were measured using jets clustered with the anti-kt algorithm with parameters R = 0.4 and R = 0.6. These measurements are based on the 2010 data sample, consisting of a total integrated luminosity of 37 pb(-1). Inclusive jet double-differential cross sections are presented as a function of jet transverse momentum, in bins of jet rapidity. Dijet double-differential cross sections are studied as a function of the dijet invariant mass, in bins of half the rapidity separation of the two leading jets. The measurements are performed in the jet rapidity range vertical bar y vertical bar < 4.4, covering jet transverse momenta from 20 GeV to 1.5 TeV and dijet invariant masses from 70 GeV to 5 TeV. The data are compared to expectations based on next-to-leading-order QCD calculations corrected for nonperturbative effects, as well as to next-to-leading-order Monte Carlo predictions. In addition to a test of the theory in a new kinematic regime, the data also provide sensitivity to parton distribution functions in a region where they are currently not well-constrained.
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| 3. |
- Aad, G., et al.
(författare)
-
A study of the material in the ATLAS inner detector using secondary hadronic interactions
- 2012
-
Ingår i: Journal of Instrumentation. - IOP Publishing Ltd. - 1748-0221. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- The ATLAS inner detector is used to reconstruct secondary vertices due to hadronic interactions of primary collision products, so probing the location and amount of material in the inner region of ATLAS. Data collected in 7 TeV pp collisions at the LHC, with a minimum bias trigger, are used for comparisons with simulated events. The reconstructed secondary vertices have spatial resolutions ranging from similar to 200 mu m to 1 mm. The overall material description in the simulation is validated to within an experimental uncertainty of about 7%. This will lead to a better understanding of the reconstruction of various objects such as tracks, leptons, jets, and missing transverse momentum.
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| 4. |
- Aad, G., et al.
(författare)
-
Inclusive search for same-sign dilepton signatures in pp collisions at root s=7 TeV with the ATLAS detector
- 2011
-
Ingår i: Journal of High Energy Physics. - Springer. - 1126-6708. ; :10, s. 107
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Tidskriftsartikel (refereegranskat)abstract
- An inclusive search is presented for new physics in events with two isolated leptons (e or mu) having the same electric charge. The data are selected from events collected from p p collisions at root s = 7 TeV by the ATLAS detector and correspond to an integrated luminosity of 34 pb(-1). The spectra in dilepton invariant mass, missing transverse momentum and jet multiplicity are presented and compared to Standard Model predictions. In this event sample, no evidence is found for contributions beyond those of the Standard Model. Limits are set on the cross-section in a fiducial region for new sources of same-sign high-mass dilepton events in the ee, e mu and mu mu channels. Four models predicting same-sign dilepton signals are constrained: two descriptions of Majorana neutrinos, a cascade topology similar to supersymmetry or universal extra dimensions, and fourth generation d-type quarks. Assuming a new physics scale of 1 TeV, Majorana neutrinos produced by an effective operator V with masses below 460 GeV are excluded at 95% confidence level. A lower limit of 290 GeV is set at 95% confidence level on the mass of fourth generation d-type quarks.
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| 5. |
- Aad, G., et al.
(författare)
-
Limits on the production of the standard model Higgs boson 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. ; 71:9
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Tidskriftsartikel (refereegranskat)abstract
- A search for the Standard Model Higgs boson at the Large Hadron Collider (LHC) running at a centre-of-mass energy of 7 TeV is reported, based on a total integrated luminosity of up to 40 pb(-1) collected by the ATLAS detector in 2010. Several Higgs boson decay channels: H -> gamma gamma, H -> ZZ(()*()) -> llll, H -> ZZ -> LL nu nu, H -> ZZ -> llqq, H -> WW(*()) -> l nu l nu and H -> WW -> l nu qq (l is e, mu) are combined in a mass range from 110 GeV to 600 GeV. The highest sensitivity is achieved in the mass range between 160 GeV and 170 GeV, where the expected 95% CL exclusion sensitivity is at Higgs boson production cross sections 2.3 times the Standard Model prediction. Upper limits on the cross section for its production are determined. Models with a fourth generation of heavy leptons and quarks with Standard Model-like couplings to the Higgs boson are also investigated and are excluded at 95% CL for a Higgs boson mass in the range from 140 GeV to 185 GeV.
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| 6. |
- Aad, G., et al.
(författare)
-
Measurement of multi-jet cross sections in proton-proton collisions at a 7 TeV center-of-mass energy
- 2011
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Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 71:11
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Tidskriftsartikel (refereegranskat)abstract
- Inclusive multi-jet production is studied in proton-proton collisions at a center-of-mass energy of 7 TeV, using the ATLAS detector. The data sample corresponds to an integrated luminosity of 2.4 pb(-1). Results on multi-jet cross sections are presented and compared to both leading-order plus parton-shower Monte Carlo predictions and to next-to-leading-order QCD calculations.
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| 7. |
- Aad, G., et al.
(författare)
-
Measurement of the azimuthal ordering of charged hadrons with the ATLAS detector
- 2012
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Ingår i: Physical Review D. - American Physical Society. - 1550-7998. ; 86:5, s. 052005
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study of the possible ordering of charged hadrons in the azimuthal angle relative to the beam axis in high-energy proton-proton collisions at the Large Hadron Collider (LHC). A spectral analysis of correlations between longitudinal and transverse components of the momentum of the charged hadrons, driven by the search for phenomena related to the structure of the QCD field, is performed. Data were recorded with the ATLAS detector at center-of-mass energies of root s = 900 GeV and root s = 7 TeV. The correlations measured in a kinematic region dominated by low-p(T) particles are not well described by conventional models of hadron production. The measured spectra show features consistent with the fragmentation of a QCD string represented by a helixlike ordered gluon chain.
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| 8. |
- Aad, G., et al.
(författare)
-
Measurement of the centrality dependence of the charged particle pseudorapidity distribution in lead-lead collisions at root s(NN)=2.76 TeV with the ATLAS detector
- 2012
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Ingår i: Physics Letters B. - Elsevier Science Bv. - 0370-2693. ; 710:3, s. 363-382
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Tidskriftsartikel (refereegranskat)abstract
- The ATLAS experiment at the LHC has measured the centrality dependence of charged particle pseudorapidity distributions over vertical bar eta vertical bar < 2 in lead-lead collisions at a nucleon-nucleon centre-of-mass energy of root s(NN) = 2.76 TeV. In order to include particles with transverse momentum as low as 30 MeV, the data were recorded with the central solenoid magnet off. Charged particles were reconstructed with two algorithms (2-point "tracklets" and full tracks) using information from the pixel detector only. The lead-lead collision centrality was characterized by the total transverse energy in the forward calorimeter in the range 3.2 < vertical bar eta vertical bar< 4.9. Measurements are presented of the per-event charged particle pseudorapidity distribution, dN(ch)/d eta, and the average charged particle multiplicity in the pseudorapidity interval vertical bar eta vertical bar < 0.5 in several intervals of collision centrality. The results are compared to previous mid-rapidity measurements at the LHC and RHIC. The variation of the mid-rapidity charged particle yield per colliding nucleon pair with the number of participants is consistent with lower root s(NN) results. The shape of the dN(ch)/d eta distribution is found to be independent of centrality within the systematic uncertainties of the measurement. (C) 2012 CERN. Published by Elsevier B.V. All rights reserved.
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| 9. |
- Aad, G., et al.
(författare)
-
Measurement of the cross section for top-quark pair production in pp collisions at root s=7 TeV with the ATLAS detector using final states with two high-p(T) leptons
- 2012
-
Ingår i: Journal of High Energy Physics. - Springer. - 1126-6708. ; :5, s. 59
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Tidskriftsartikel (refereegranskat)abstract
- A measurement is reported of the production cross section of top-quark pairs (t (t) over bar) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the LHC. Candidate events have a signature consistent with containing two isolated leptons, large missing transverse momentum, and at least two jets. Using a data sample corresponding to an integrated luminosity of 0.70 fb(-1), a t (t) over bar production cross section sigma(t (t) over bar) = 176 +/- 5(stat.)(-11)(+14)(syst.) +/- 8(lum.) pb is measured for an assumed top-quark mass of m(t) = 172.5 GeV. This measurement is in good agreement with Standard Model predictions.
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| 10. |
- Aad, G., et al.
(författare)
-
Measurement of the production cross section of an isolated photon associated with jets in proton-proton collisions at root s=7 TeV with the ATLAS detector
- 2012
-
Ingår i: Physical Review D. - American Physical Society. - 1550-7998. ; 85:9
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of the cross section for the production of an isolated photon in association with jets in proton-proton collisions at a center-of-mass energy root s = 7 TeV is presented. Photons are reconstructed in the pseudorapidity range vertical bar eta(gamma)vertical bar < 1.37 and with a transverse energy E-T(gamma) > 25 GeV. Jets are reconstructed in the rapidity range vertical bar y(jet)vertical bar < 4.4 and with a transverse momentum p(T)(jet) > 20 GeV. The differential cross section d sigma/dE(T)(gamma) is measured, as a function of the photon transverse energy, for three different rapidity ranges of the leading-p(T) jet: vertical bar y(jet)vertical bar < 1.2, 1.2 <= vertical bar y(jet)vertical bar < 2.8 and 2.8 <= vertical bar y(jet)vertical bar < 4.4. For each rapidity configuration the same-sign (eta(gamma)y(jet) >= 0) and opposite-sign (eta(gamma) y(jet) < 0) cases are studied separately. The results are based on an integrated luminosity of 37 pb(-1), collected with the ATLAS detector at the LHC. Next-to-leading order perturbative QCD calculations are found to be in fair agreement with the data, except for E-T(gamma) <= 45 GeV, where the theoretical predictions overestimate the measured cross sections.
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