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Sökning: LAR1:lu > Abdinov O

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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)
  • 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.
5.
  • 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.
6.
  • 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).
7.
  • Aaboud, M, et al. (författare)
  • Determination of the strong coupling constant αs from transverse energy–energy correlations in multijet events at √s=8TeV using the ATLAS detector
  • 2017
  • Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 77:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements of transverse energy–energy correlations and their associated asymmetries in multi-jet events using the ATLAS detector at the LHC are presented. The data used correspond to s=8TeV proton–proton collisions with an integrated luminosity of 20.2fb-1. The results are presented in bins of the scalar sum of the transverse momenta of the two leading jets, unfolded to the particle level and compared to the predictions from Monte Carlo simulations. A comparison with next-to-leading-order perturbative QCD is also performed, showing excellent agreement within the uncertainties. From this comparison, the value of the strong coupling constant is extracted for different energy regimes, thus testing the running of αs(μ) predicted in QCD up to scales over 1TeV. A global fit to the transverse energy–energy correlation distributions yields αs(mZ)=0.1162±0.0011(exp.)-0.0070+0.0084(theo.), while a global fit to the asymmetry distributions yields a value of αs(mZ)=0.1196±0.0013(exp.)-0.0045+0.0075(theo.). © 2017, CERN for the benefit of the ATLAS collaboration.
8.
  • Aaboud, M, et al. (författare)
  • Direct top-quark decay width measurement in the tt¯ lepton+jets channel at √s=8TeV with the ATLAS experiment
  • 2018
  • Ingår i: European Physical Journal C. - Springer. - 1434-6044. ; 78:2
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents a direct measurement of the decay width of the top quark using tt¯ events in the lepton+jets final state. The data sample was collected by the ATLAS detector at the LHC in proton–proton collisions at a centre-of-mass energy of 8 TeV and corresponds to an integrated luminosity of 20.2 fb- 1. The decay width of the top quark is measured using a template fit to distributions of kinematic observables associated with the hadronically and semileptonically decaying top quarks. The result, Γt=1.76±0.33(stat.)-0.68+0.79(syst.)GeV for a top-quark mass of 172.5 GeV, is consistent with the prediction of the Standard Model. © 2018, CERN for the benefit of the ATLAS collaboration.
9.
  • Aaboud, M, et al. (författare)
  • Electron efficiency measurements with the ATLAS detector using 2012 LHC proton-proton collision data
  • 2017
  • Ingår i: European Physical Journal C. - 1434-6044. ; 77:3
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper describes the algorithms for the reconstruction and identification of electrons in the central region of the ATLAS detector at the Large Hadron Collider (LHC). These algorithms were used for all ATLAS results with electrons in the final state that are based on the 2012 pp collision data produced by the LHC at root s = 8 TeV. The efficiency of these algorithms, together with the charge misidentification rate, is measured in data and evaluated in simulated samples using electrons from Z -&gt; ee, Z -&gt; ee gamma and J/Psi -&gt; ee decays. For these efficiency measurements, the full recorded data set, corresponding to an integrated luminosity of 20.3 fb(-1), is used. Based on a new reconstruction algorithm used in 2012, the electron reconstruction efficiency is 97% for electrons with E-T = 15 GeV and 99% at E-T = 50 GeV. Combining this with the efficiency of additional selection criteria to reject electrons from background processes or misidentified hadrons, the efficiency to reconstruct and identify electrons at the ATLAS experiment varies from 65 to 95%, depending on the transverse momentum of the electron and background rejection.
10.
  • Aaboud, M., et al. (författare)
  • Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector
  • 2018
  • Ingår i: Physical Review D. - American Physical Society. - 1550-2368. ; 97:7
  • Tidskriftsartikel (refereegranskat)abstract
    • A search for the associated production of the Higgs boson with a top quark pair (ttH) is reported. The search is performed in multilepton final states using a data set corresponding to an integrated luminosity of 36.1 fb-1 of proton-proton collision data recorded by the ATLAS experiment at a center-of-mass energy s=13 TeV at the Large Hadron Collider. Higgs boson decays to WW∗, ττ, and ZZ∗ are targeted. Seven final states, categorized by the number and flavor of charged-lepton candidates, are examined for the presence of the Standard Model Higgs boson with a mass of 125 GeV and a pair of top quarks. An excess of events over the expected background from Standard Model processes is found with an observed significance of 4.1 standard deviations, compared to an expectation of 2.8 standard deviations. The best fit for the ttH production cross section is σ(ttH)=790-210+230 fb, in agreement with the Standard Model prediction of 507-50+35 fb. The combination of this result with other ttH searches from the ATLAS experiment using the Higgs boson decay modes to bb, γγ and ZZ∗→4, has an observed significance of 4.2 standard deviations, compared to an expectation of 3.8 standard deviations. This provides evidence for the ttH production mode. © 2018 CERN, for the ATLAS Collaboration. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.
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