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1.
  • Aaboud, M., et al. (författare)
  • A measurement of the calorimeter response to single hadrons and determination of the jet energy scale uncertainty using LHC Run-1 pp-collision data with the ATLAS detector
  • 2017
  • Ingår i: European Physical Journal C. - 1434-6044. ; 77:1
  • Tidskriftsartikel (refereegranskat)abstract
    • A measurement of the calorimeter response to isolated charged hadrons in the ATLAS detector at the LHC is presented. This measurement is performed with 3.2 nb(-1) of proton-proton collision data at root s = 7 TeV from 2010 and 0.1 nb(-1) of data at root s = 8 TeV from 2012. A number of aspects of the calorimeter response to isolated hadrons are explored. After accounting for energy deposited by neutral particles, there is a 5% discrepancy in the modelling, using various sets of GEANT4 hadronic physics models, of the calorimeter response to isolated charged hadrons in the central calorimeter region. The description of the response to anti-protons at low momenta is found to be improved with respect to previous analyses. The electromagnetic and hadronic calorimeters are also examined separately, and the detector simulation is found to describe the response in the hadronic calorimeter well. The jet energy scale uncertainty and correlations in scale between jets of different momenta and pseudorapidity are derived based on these studies. The uncertainty is 2-5% for jets with transverse momenta above 2 TeV, where this method provides the jet energy scale uncertainty for ATLAS.
2.
  • Aaboud, M, et al. (författare)
  • A search for pair-produced resonances in four-jet final states at √s=13 TeV with the ATLAS detector
  • 2018
  • Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 78:3
  • Tidskriftsartikel (refereegranskat)abstract
    • A search for massive coloured resonances which are pair-produced and decay into two jets is presented. The analysis uses 36.7 fb- 1 of s = 13 TeV pp collision data recorded by the ATLAS experiment at the LHC in 2015 and 2016. No significant deviation from the background prediction is observed. Results are interpreted in a SUSY simplified model where the lightest supersymmetric particle is the top squark, t~ , which decays promptly into two quarks through R-parity-violating couplings. Top squarks with masses in the range 100GeV<mt~<410 GeV are excluded at 95% confidence level. If the decay is into a b-quark and a light quark, a dedicated selection requiring two b-tags is used to exclude masses in the ranges 100GeV<mt~<470 GeV and 480GeV<mt~<610 GeV. Additional limits are set on the pair-production of massive colour-octet resonances. © 2018, CERN for the benefit of the ATLAS collaboration.
3.
  • Aaboud, M, et al. (författare)
  • Analysis of the Wtb vertex from the measurement of triple-differential angular decay rates of single top quarks produced in the t-channel at √s=8 TeV with the ATLAS detector
  • 2017
  • Ingår i: Journal of High Energy Physics. - Springer. - 1126-6708. ; 2017:12
  • Tidskriftsartikel (refereegranskat)abstract
    • The electroweak production and subsequent decay of single top quarks in the t-channel is determined by the properties of the Wtb vertex, which can be described by the complex parameters of an effective Lagrangian. An analysis of a triple-differential decay rate in t-channel production is used to simultaneously determine five generalised helicity fractions and phases, as well as the polarisation of the produced top quark. The complex parameters are then constrained. This analysis is based on 20.2 fb−1 of proton-proton collision data at a centre-of-mass energy of 8 TeV collected with the ATLAS detector at the LHC. The fraction of decays containing transversely polarised W bosons is measured to be f1 = 0.30 ± 0.05. The phase between amplitudes for transversely and longitudinally polarised W bosons recoiling against left-handed b-quarks is measured to be δ− = 0.002π+ 0.017π + 0.016π, giving no indication of CP violation. The fractions of longitudinal or transverse W bosons accompanied by right-handed b-quarks are also constrained. Based on these measurements, limits are placed at 95% CL on the ratio of the complex coupling parameters Re [gR/VL ∈ [−0.12, 0.17] and Im [gR/VL ∈ [−0.07, 0.06]. Constraints are also placed on the ratios |VR/VL| and |gL/VL|. In addition, the polarisation of single top quarks in the t-channel is constrained to be P > 0.72 (95% CL). None of the above measurements make assumptions about the value of any of the other parameters or couplings and all of them are in agreement with the Standard Model.[Figure not available: see fulltext.]. © 2017, The Author(s).
4.
  • Aaboud, M, et al. (författare)
  • Angular analysis of Bd 0 → K ∗ μ + μ − decays in pp collisions at √s=8 TeV with the ATLAS detector
  • 2018
  • Ingår i: Journal of High Energy Physics. - Springer. - 1126-6708. ; 2018:10
  • Tidskriftsartikel (refereegranskat)abstract
    • An angular analysis of the decay Bd 0 → K∗μ+μ− is presented, based on proton-proton collision data recorded by the ATLAS experiment at the LHC. The study is using 20.3 fb−1 of integrated luminosity collected during 2012 at centre-of-mass energy of s=8 TeV. Measurements of the K* longitudinal polarisation fraction and a set of angular parameters obtained for this decay are presented. The results are compatible with the Standard Model predictions.[Figure not available: see fulltext.]. © 2018, The Author(s).
5.
  • Aaboud, M, et al. (författare)
  • Charged-particle distributions at low transverse momentum in √s=13 TeV pp interactions measured with the ATLAS detector at the LHC
  • 2016
  • Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 76:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements of distributions of charged particles produced in proton–proton collisions with a centre-of-mass energy of 13 TeV are presented. The data were recorded by the ATLAS detector at the LHC and correspond to an integrated luminosity of 151 μ b - 1. The particles are required to have a transverse momentum greater than 100 MeV and an absolute pseudorapidity less than 2.5. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on multiplicity are measured in events containing at least two charged particles satisfying the above kinematic criteria. The results are corrected for detector effects and compared to the predictions from several Monte Carlo event generators. © 2016, CERN for the benefit of the ATLAS collaboration.
6.
  • Aaboud, M, et al. (författare)
  • Combination of inclusive and differential (Formula Presented) charge asymmetry measurements using ATLAS and CMS data at (Formula Presented)= 7 and 8 TeV
  • 2018
  • Ingår i: Journal of High Energy Physics. - Springer. - 1126-6708. ; 2018:4
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents combinations of inclusive and differential measurements of the charge asymmetry (AC) in top quark pair (tt) events with a lepton+jets signature by the ATLAS and CMS Collaborations, using data from LHC proton-proton collisions at centreof- mass energies of 7 and 8TeV. The data correspond to integrated luminosities of about 5 and 20 fb–1for each experiment, respectively. The resulting combined LHC measurements of the inclusive charge asymmetry are AC LHC7= 0:005±0:007 (stat) ±0:006 (syst) at 7TeV and AC LHC7= 0:0055 ± 0:0023 (stat) ± 0:0025 (syst) at 8TeV. These values, as well as the combination of AC measurements as a function of the invariant mass of the [formula presented] system at 8TeV, are consistent with the respective standard model predictions. © CERN, for the benefit of the ATLAS-CMS Collaboration.
7.
  • Aaboud, M, et al. (författare)
  • Combination of searches for heavy resonances decaying into bosonic and leptonic final states using 36 fb-1 of proton-proton collision data at s =13 TeV with the ATLAS detector
  • 2018
  • Ingår i: Physical Review D. - American Physical Society. - 1550-2368. ; 98:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Searches for new heavy resonances decaying into different pairings of W, Z, or Higgs bosons, as well as directly into leptons, are presented using a data sample corresponding to 36.1 fb-1 of pp collisions at s=13 TeV collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Analyses selecting bosonic decay modes in the qqqq, ννqq, ℓνqq, ℓℓqq, ℓνℓν, ℓℓνν, ℓνℓℓ, ℓℓℓℓ, qqbb, ννbb, ℓνbb, and ℓℓbb final states are combined, searching for a narrow-width resonance. Likewise, analyses selecting the leptonic ℓν and ℓℓ final states are also combined. These two sets of analyses are then further combined. No significant deviation from the Standard Model predictions is observed. Three benchmark models are tested: a model predicting the existence of a new heavy scalar singlet, a simplified model predicting a heavy vector-boson triplet, and a bulk Randall-Sundrum model with a heavy spin-2 Kaluza-Klein excitation of the graviton. Cross section limits are set at the 95% confidence level using an asymptotic approximation and are compared with predictions for the benchmark models. These limits are also expressed in terms of constraints on couplings of the heavy vector-boson triplet to quarks, leptons, and the Higgs boson. The data exclude a heavy vector-boson triplet with mass below 5.5 TeV in a weakly coupled scenario and 4.5 TeV in a strongly coupled scenario, as well as a Kaluza-Klein graviton with mass below 2.3 TeV. © 2018 CERN, for the ATLAS Collaboration.
8.
  • Aaboud, M, et al. (författare)
  • Combined measurement of differential and total cross sections in the H → γγ and the H → ZZ⁎ → 4ℓ decay channels at s=13 TeV with the ATLAS detector
  • 2018
  • Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - Elsevier. - 0370-2693. ; 786, s. 114-133
  • Tidskriftsartikel (refereegranskat)abstract
    • A combined measurement of differential and inclusive total cross sections of Higgs boson production is performed using 36.1 fb−1 of 13 TeV proton–proton collision data produced by the LHC and recorded by the ATLAS detector in 2015 and 2016. Cross sections are obtained from measured H→γγ and H→ZZ⁎→4ℓ event yields, which are combined taking into account detector efficiencies, resolution, acceptances and branching fractions. The total Higgs boson production cross section is measured to be 57.0−5.9 +6.0 (stat.) −3.3 +4.0 (syst.) pb, in agreement with the Standard Model prediction. Differential cross-section measurements are presented for the Higgs boson transverse momentum distribution, Higgs boson rapidity, number of jets produced together with the Higgs boson, and the transverse momentum of the leading jet. The results from the two decay channels are found to be compatible, and their combination agrees with the Standard Model predictions. © 2018 The Author(s)
9.
  • Aaboud, M, et al. (författare)
  • Constraints on off-shell Higgs boson production and the Higgs boson total width in ZZ → 4ℓ and ZZ → 2ℓ2ν final states with the ATLAS detector
  • 2018
  • Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - Elsevier. - 0370-2693. ; 786, s. 223-244
  • Tidskriftsartikel (refereegranskat)abstract
    • A measurement of off-shell Higgs boson production in the ZZ→4ℓ and ZZ→2ℓ2ν decay channels, where ℓ stands for either an electron or a muon, is performed using data from proton–proton collisions at a centre-of-mass energy of s=13 TeV. The data were collected by the ATLAS experiment in 2015 and 2016 at the Large Hadron Collider, and they correspond to an integrated luminosity of 36.1fb−1. An observed (expected) upper limit on the off-shell Higgs signal strength, defined as the event yield normalised to the Standard Model prediction, of 3.8 (3.4) is obtained at 95% confidence level (CL). Assuming the ratio of the Higgs boson couplings to the Standard Model predictions is independent of the momentum transfer of the Higgs production mechanism considered in the analysis, a combination with the on-shell signal-strength measurements yields an observed (expected) 95% CL upper limit on the Higgs boson total width of 14.4 (15.2) MeV. © 2018 The Author
10.
  • Aaboud, M, et al. (författare)
  • Dark matter interpretations of ATLAS searches for the electroweak production of supersymmetric particles in √s=8 TeV proton-proton collisions
  • 2016
  • Ingår i: Journal of High Energy Physics. - Springer. - 1126-6708. ; 2016:9
  • Tidskriftsartikel (refereegranskat)abstract
    • A selection of searches by the ATLAS experiment at the LHC for the electroweak production of SUSY particles are used to study their impact on the constraints on dark matter candidates. The searches use 20 fb−1 of proton-proton collision data at s=8 TeV. A likelihood-driven scan of a five-dimensional effective model focusing on the gaugino-higgsino and Higgs sector of the phenomenological minimal supersymmetric Standard Model is performed. This scan uses data from direct dark matter detection experiments, the relic dark matter density and precision flavour physics results. Further constraints from the ATLAS Higgs mass measurement and SUSY searches at LEP are also applied. A subset of models selected from this scan are used to assess the impact of the selected ATLAS searches in this five-dimensional parameter space. These ATLAS searches substantially impact those models for which the mass m(χ˜10) of the lightest neutralino is less than 65 GeV, excluding 86% of such models. The searches have limited impact on models with larger m(χ˜10) due to either heavy electroweakinos or compressed mass spectra where the mass splittings between the produced particles and the lightest supersymmetric particle is small.[Figure not available: see fulltext.] © 2016, The Author(s).
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