| 1. |
- Milstead, David A., et al.
(author)
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Study of the material of the ATLAS inner detector for Run 2 of the LHC
- 2017
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In: Journal of Instrumentation. - : Institute of Physics (IOP). - 1748-0221. ; 12:12
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Journal article (peer-reviewed)abstract
- The ATLAS inner detector comprises three different sub-detectors: the pixel detector, the silicon strip tracker, and the transition-radiation drift-tube tracker. The Insertable B-Layer, a new innermost pixel layer, was installed during the shutdown period in 2014, together with modifications to the layout of the cables and support structures of the existing pixel detector. The material in the inner detector is studied with several methods, using a low-luminosity s=13 TeV pp collision sample corresponding to around 2.0 nb-1 collected in 2015 with the ATLAS experiment at the LHC. In this paper, the material within the innermost barrel region is studied using reconstructed hadronic interaction and photon conversion vertices. For the forward rapidity region, the material is probed by a measurement of the efficiency with which single tracks reconstructed from pixel detector hits alone can be extended with hits on the track in the strip layers. The results of these studies have been taken into account in an improved description of the material in the ATLAS inner detector simulation, resulting in a reduction in the uncertainties associated with the charged-particle reconstruction efficiency determined from simulation. © 2017 CERN.
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| 2. |
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| 3. |
- Aad, G., et al.
(author)
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Identification and energy calibration of hadronically decaying tau leptons with the ATLAS experiment in pp collisions at root s=8 TeV
- 2015
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In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 75:7
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Journal article (peer-reviewed)abstract
- This paper describes the trigger and offline reconstruction, identification and energy calibration algorithms for hadronic decays of tau leptons employed for the data collected from pp collisions in 2012 with the ATLAS detector at the LHC center-of-mass energy root s = 8 TeV. The performance of these algorithms is measured in most cases with Z decays to tau leptons using the full 2012 dataset, corresponding to an integrated luminosity of 20.3 fb(-1). An uncertainty on the offline reconstructed tau energy scale of 2-4%, depending on transverse energy and pseudorapidity, is achieved using two independent methods. The offline tau identification efficiency is measured with a precision of 2.5% for hadronically decaying tau leptons with one associated track, and of 4% for the case of three associated tracks, inclusive in pseudorapidity and for a visible transverse energy greater than 20 GeV. For hadronic tau lepton decays selected by offline algorithms, the tau trigger identification efficiency is measured with a precision of 2-8%, depending on the transverse energy. The performance of the tau algorithms, both offline and at the trigger level, is found to be stable with respect to the number of concurrent proton-proton interactions and has supported a variety of physics results using hadronically decaying tau leptons at ATLAS.
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| 4. |
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| 5. |
- Abulaiti, Yiming, et al.
(author)
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Charged-particle distributions in root s=13 TeV pp interactions measured with the ATLAS detector at the LHC
- 2016
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In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 758, s. 67-88
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Journal article (peer-reviewed)abstract
- Charged-particle distributions are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV, using a data sample of nearly 9 million events, corresponding to an integrated luminosity of 170 mu b(-1), recorded by the ATLAS detector during a special Large Hadron Collider fill. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on the charged-particle multiplicity are presented. The measurements are performed with charged particles with transverse momentum greater than 500 MeV and absolute pseudorapidity less than 2.5, in events with at least one charged particle satisfying these kinematic requirements. Additional measurements in a reduced phase space with absolute pseudorapidity less than 0.8 are also presented, in order to compare with other experiments. The results are corrected for detector effects, presented as particle-level distributions and are compared to the predictions of various Monte Carlo event generators.
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| 6. |
- Abulaiti, Yiming, et al.
(author)
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Fiducial, total and differential cross-section measurements of t-channel single top-quark production in pp collisions at 8TeV using data collected by the ATLAS detector
- 2017
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 77:8
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Journal article (peer-reviewed)abstract
- Detailed measurements of t-channel single top-quark production are presented. They use 20.2 fb(-1) of data collected by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of 8 TeV at the LHC. Total, fiducial and differential cross-sections are measured for both top-quark and top-antiquark production. The fiducial cross-section is measured with a precision of 5.8% (top quark) and 7.8% (top antiquark), respectively. The total cross-sections are measured to be stot(tq) = 56.7(-3.8)(+4.3) pb for top-quark production and sigma(tot)((t) over barq) = 32.9(-2.7)(+3.0) pb for top-antiquark production, in agreement with the Standard Model prediction. In addition, the ratio of top-quark to top-antiquark production cross-sections is determined to be R-t = 1.72 +/- 0.09. The differential cross-sections as a function of the transverse momentum and rapidity of both the top quark and the top antiquark are measured at both the parton and particle levels. The transverse momentum and rapidity differential cross-sections of the accompanying jet from the t-channel scattering are measured at particle level. All measurements are compared to various Monte Carlo predictions as well as to fixed-order QCD calculations where available.
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| 7. |
- Abulaiti, Yiming, et al.
(author)
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Jet energy scale measurements and their systematic uncertainties in proton-proton collisions at root s=13 TeV with the ATLAS detector
- 2017
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In: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 96:7
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Journal article (peer-reviewed)abstract
- Jet energy scale measurements and their systematic uncertainties are reported for jets measured with the ATLAS detector using proton-proton collision data with a center-of-mass energy of root s = 13 TeV, corresponding to an integrated luminosity of 3.2 fb(-1) collected during 2015 at the LHC. Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells, using the anti-k(t) algorithm with radius parameter R = 0.4. Jets are calibrated with a series of simulation-based corrections and in situ techniques. In situ techniques exploit the transverse momentum balance between a jet and a reference object such as a photon, Z boson, or multijet system for jets with 20 < p(T) < 2000 GeV and pseudorapidities of vertical bar eta vertical bar < 4.5, using both data and simulation. An uncertainty in the jet energy scale of less than 1% is found in the central calorimeter region (vertical bar eta vertical bar < 1.2) for jets with 100 < p(T) < 500 GeV. An uncertainty of about 4.5% is found for low-p(T) jets with p(T) = 20 GeV in the central region, dominated by uncertainties in the corrections for multiple proton-proton interactions. The calibration of forward jets (vertical bar eta vertical bar > 0.8) is derived from dijet p(T) balance measurements. For jets of p(T) = 80 GeV, the additional uncertainty for the forward jet calibration reaches its largest value of about 2% in the range vertical bar eta vertical bar > 3.5 and in a narrow slice of 2.2 < vertical bar eta vertical bar < 2.4.
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| 8. |
- Abulaiti, Yiming, et al.
(author)
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Measurement of exclusive gamma gamma -> W+W- production and search for exclusive Higgs boson production in pp collisions at root s=8 TeV using the ATLAS detector
- 2016
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In: Physical Review D. - 2470-0010 .- 1550-7998 .- 1550-2368. ; 94:3
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Journal article (peer-reviewed)abstract
- Searches for exclusively produced W boson pairs in the process pp(gamma gamma) -> pW(+) W- p and an exclusively produced Higgs boson in the process pp(gg) -> pHp have been performed using e(+/-) mu(-/+) final states. These measurements use 20.2 fb(-1) of pp collisions collected by the ATLAS experiment at a center-of-mass energy root s = 8 TeV at the LHC. Exclusive production of W+ W- consistent with the Standard Model prediction is found with 3.0 sigma significance. The exclusive W+ W- production cross section is determined to be sigma(gamma gamma -> W+ W- -> e(+/-) mu(-/+) X) = 6.9 +/- 2.2(stat) +/- 1.4(sys) fb, in agreement with the Standard Model prediction. Limits on anomalous quartic gauge couplings are set at 95% confidence level as -1.7 x 10(-6) < a(0)(W) / Lambda(2) < 1.7 x 10(-6) GeV-2 and -6.4 x 10(-6) < a(C)(W) / Lambda(2) < 6.3 x 10(-6) GeV-2. A 95% confidence-level upper limit on the total production cross section for an exclusive Higgs boson is set to 1.2 pb.
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| 9. |
- Abulaiti, Yiming, et al.
(author)
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Measurement of the b(b)over-bar dijet cross section in pp collisions at root s=7TeV with the ATLAS detector
- 2016
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:12
-
Journal article (peer-reviewed)abstract
- The dijet production cross section for jets containing a b-hadron (b-jets) has been measured in protonproton collisions with a centre-of-mass energy of root s = 7TeV, using the ATLAS detector at the LHC. The data used correspond to an integrated luminosity of 4.2 fb(-1). The cross section is measured for events with two identified b-jets with a transverse momentum pT > 20GeV and a minimum separation in the eta-phi plane of Delta R = 0.4. At least one of the jets in the event is required to have p(T) > 270GeV. The cross section is measured differentially as a function of dijet invariant mass, dijet transverse momentum, boost of the dijet system, and the rapidity difference, azimuthal angle and angular distance between the b-jets. The results are compared to different predictions of leading order and next-to-leading order perturbative quantum chromodynamics matrix elements supplemented with models for parton-showers and hadronization.
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| 10. |
- Abulaiti, Yiming, et al.
(author)
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Measurement of the cross-section for electroweak production of dijets in association with a Z boson in pp collisions at root s=13 TeV with the ATLAS detector
- 2017
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 775, s. 206-228
-
Journal article (peer-reviewed)abstract
- The cross-section for the production of two jets in association with a leptonically decaying Z boson (Zjj) is measured in proton-proton collisions at a centre-of-mass energy of 13 TeV, using data recorded with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 3.2 fb(-1). The electroweak Zjj cross-section is extracted in a fiducial region chosen to enhance the electroweak contribution relative to the dominant Drell-Yan Zjj process, which is constrained using a data-driven approach. The measured fiducial electroweak cross-section is sigma(Zjj)(EW) = 119 +/- 16 (stat.) +/- 20 (syst.) +/- 2 (lumi.) fb for dijet invariant mass greater than 250 GeV, and 34.2 +/- 5.8 (stat.) +/- 5.5 (syst.) +/- 0.7 (lumi.) fb for dijet invariant mass greater than 1 TeV. Standard Model predictions are in agreement with the measurements. The inclusive Zjj cross-section is also measured in six different fiducial regions with varying contributions from electroweak and Drell-Yan Zjj production.
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