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Sökning: WFRF:(Ekman C J) > Kungliga Tekniska Högskolan

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1.
  • Mach, H., et al. (författare)
  • Application of ultra-fast timing techniques to the study of exotic and weakly produced nuclei
  • 2005
  • Ingår i: Journal of Physics G. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 31:10, s. S1421-S1426
  • Tidskriftsartikel (refereegranskat)abstract
    • Ultra-fast time-delayed techniques have been recently applied in a number of studies where exotic nuclei were identified using advanced selection techniques. These include large Compton-suppressed Ge arrays, in-flight separators or recoil separators. Some of the new results are discussed in this presentation. Besides the results for Mg-32 and Pd-96, they include the first determination of the half-life of the 8(+) state in Ge-80, T-1/2 = 2.95(6) ns, and significantly more precise results for Mn-51 (3680 keV level) and V-48 (421 keV level), T-1/2 = 1760(40) ps and T-1/2.
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2.
  • Mullier, G.A., et al. (författare)
  • Constraints on spin-0 dark matter mediators and invisible Higgs decays using ATLAS 13 TeV pp collision data with two top quarks and missing transverse momentum in the final state
  • 2023
  • Ingår i: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:6
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents a statistical combination of searches targeting final states with two top quarks and invisible particles, characterised by the presence of zero, one or two leptons, at least one jet originating from a b-quark and missing transverse momentum. The analyses are searches for phenomena beyond the Standard Model consistent with the direct production of dark matter in pp collisions at the LHC, using 139 fb - 1 of data collected with the ATLAS detector at a centre-of-mass energy of 13 TeV. The results are interpreted in terms of simplified dark matter models with a spin-0 scalar or pseudoscalar mediator particle. In addition, the results are interpreted in terms of upper limits on the Higgs boson invisible branching ratio, where the Higgs boson is produced according to the Standard Model in association with a pair of top quarks. For scalar (pseudoscalar) dark matter models, with all couplings set to unity, the statistical combination extends the mass range excluded by the best of the individual channels by 50 (25) GeV, excluding mediator masses up to 370 GeV. In addition, the statistical combination improves the expected coupling exclusion reach by 14% (24%), assuming a scalar (pseudoscalar) mediator mass of 10 GeV. An upper limit on the Higgs boson invisible branching ratio of 0.38 (0.30-0.09+0.13) is observed (expected) at 95% confidence level. © 2023, The Author(s).
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3.
  • Mullier, G.A., et al. (författare)
  • Search for pair-produced scalar and vector leptoquarks decaying into third-generation quarks and first- or second-generation leptons in pp collisions with the ATLAS detector
  • 2023
  • Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2023:6
  • Tidskriftsartikel (refereegranskat)abstract
    • A search for pair-produced scalar and vector leptoquarks decaying into quarks and leptons of different generations is presented. It uses the full LHC Run 2 (2015–2018) data set of 139 fb−1 collected with the ATLAS detector in proton–proton collisions at a centre-of-mass energy of s = 13 TeV. Scalar leptoquarks with charge −(1/3)e as well as scalar and vector leptoquarks with charge +(2/3)e are considered. All possible decays of the pair-produced leptoquarks into quarks of the third generation (t, b) and charged or neutral leptons of the first or second generation (e, μ, ν) with exactly one electron or muon in the final state are investigated. No significant deviations from the Standard Model expectation are observed. Upper limits on the production cross-section are provided for eight models as a function of the leptoquark mass and the branching ratio of the leptoquark into the charged or neutral lepton. In addition, lower limits on the leptoquark masses are derived for all models across a range of branching ratios. Two of these models have the goal of providing an explanation for the recent B-anomalies. In both models, a vector leptoquark decays into charged and neutral leptons of the second generation with a similar branching fraction. Lower limits of 1980 GeV and 1710 GeV are set on the leptoquark mass for these two models. [Figure not available: see fulltext.] © 2023, The Author(s).
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4.
  • Ölvander, J., et al. (författare)
  • Preface
  • 2018
  • Ingår i: Proceedings of NordDesign. - : The Design Society.
  • Konferensbidrag (refereegranskat)
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5.
  • Aad, G., et al. (författare)
  • Measurement of the charge asymmetry in top-quark pair production in association with a photon with the ATLAS experiment
  • 2023
  • Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 843
  • Tidskriftsartikel (refereegranskat)abstract
    • A measurement of the charge asymmetry in top-quark pair (tt¯) production in association with a photon is presented. The measurement is performed in the single-lepton tt¯ decay channel using proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN at a centre-of-mass-energy of 13 TeV during the years 2015–2018, corresponding to an integrated luminosity of 139 fb−1. The charge asymmetry is obtained from the distribution of the difference of the absolute rapidities of the top quark and antiquark using a profile likelihood unfolding approach. It is measured to be AC=−0.003±0.029 in agreement with the Standard Model expectation. © 2023 The Author(s)
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6.
  • Mullier, G.A., et al. (författare)
  • A search for new resonances in multiple final states with a high transverse momentum Z boson in √s = 13 TeV pp collisions with the ATLAS detector
  • 2023
  • Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2023:6
  • Tidskriftsartikel (refereegranskat)abstract
    • A generic search for resonances is performed with events containing a Z boson with transverse momentum greater than 100 GeV, decaying into e + e − or μ + μ −. The analysed data collected with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider correspond to an integrated luminosity of 139 fb −1. Two invariant mass distributions are examined for a localised excess relative to the expected Standard Model background in six independent event categories (and their inclusive sum) to increase the sensitivity. No significant excess is observed. Exclusion limits at 95% confidence level are derived for two cases: a model-independent interpretation of Gaussian-shaped resonances with the mass width between 3% and 10% of the resonance mass, and a specific heavy vector triplet model with the decay mode W′ → ZW → ℓℓqq. [Figure not available: see fulltext.] © 2023, The Author(s).
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7.
  • Mullier, G.A., et al. (författare)
  • Evidence for the charge asymmetry in (Formula presented.) production at √s = 13 TeV with the ATLAS detector
  • 2023
  • Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2023:8
  • Tidskriftsartikel (refereegranskat)abstract
    • Inclusive and differential measurements of the top–antitop (Formula presented.) charge asymmetry (Formula presented.) and the leptonic asymmetry (Formula presented.) are presented in proton–proton collisions at s = 13 TeV recorded by the ATLAS experiment at the CERN Large Hadron Collider. The measurement uses the complete Run 2 dataset, corresponding to an integrated luminosity of 139 fb−1, combines data in the single-lepton and dilepton channels, and employs reconstruction techniques adapted to both the resolved and boosted topologies. A Bayesian unfolding procedure is performed to correct for detector resolution and acceptance effects. The combined inclusive (Formula presented.) charge asymmetry is measured to be (Formula presented.), which differs from zero by 4.7 standard deviations. Differential measurements are performed as a function of the invariant mass, transverse momentum and longitudinal boost of the (Formula presented.) system. Both the inclusive and differential measurements are found to be compatible with the Standard Model predictions, at next-to-next-to-leading order in quantum chromodynamics perturbation theory with next-to-leading-order electroweak corrections. The measurements are interpreted in the framework of the Standard Model effective field theory, placing competitive bounds on several Wilson coefficients. [Figure not available: see fulltext.]. © 2023, The Author(s).
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8.
  • Mullier, G.A., et al. (författare)
  • Measurement of single top-quark production in the s-channel in proton–proton collisions at √s = 13 TeV with the ATLAS detector
  • 2023
  • Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2023:6
  • Tidskriftsartikel (refereegranskat)abstract
    • A measurement of single top-quark production in the s-channel is performed in proton–proton collisions at a centre-of-mass energy of 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. The dataset corresponds to an integrated luminosity of 139 fb −1. The analysis is performed on events with an electron or muon, missing transverse momentum and exactly two b-tagged jets in the final state. A discriminant based on matrix element calculations is used to separate single-top-quark s-channel events from the main background contributions, which are top-quark pair production and W-boson production in association with jets. The observed (expected) signal significance over the background-only hypothesis is 3.3 (3.9) standard deviations, and the measured cross-section is σ=8.2−2.9+3.5 pb, consistent with the Standard Model prediction of σSM=10.32−0.36+0.40 pb. [Figure not available: see fulltext.] © 2023, The Author(s).
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9.
  • Mullier, G.A., et al. (författare)
  • Measurement of the Higgs boson mass in the H → ZZ⁎ → 4ℓ decay channel using 139 fb−1 of s=13 TeV pp collisions recorded by the ATLAS detector at the LHC
  • 2023
  • Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 843
  • Tidskriftsartikel (refereegranskat)abstract
    • The mass of the Higgs boson is measured in the H→ZZ⁎→4ℓ decay channel. The analysis uses proton–proton collision data from the Large Hadron Collider at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector between 2015 and 2018, corresponding to an integrated luminosity of 139 fb−1. The measured value of the Higgs boson mass is 124.99±0.18(stat.)±0.04(syst.) GeV. In final states with muons, this measurement benefits from an improved momentum-scale calibration relative to that adopted in previous publications. The measurement also employs an analytic model that takes into account the invariant-mass resolution of the four-lepton system on a per-event basis and the output of a deep neural network discriminating signal from background events. This measurement is combined with the corresponding measurement using 7 and 8 TeV pp collision data, resulting in a Higgs boson mass of 124.94±0.17(stat.)±0.03(syst.) GeV. © 2023 The Author(s)
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10.
  • Mullier, G.A., et al. (författare)
  • Measurements of observables sensitive to colour reconnection in tt¯ events with the ATLAS detector at √s= 13 TeV
  • 2023
  • Ingår i: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:6
  • Tidskriftsartikel (refereegranskat)abstract
    • A measurement of observables sensitive to effects of colour reconnection in top-quark pair-production events is presented using 139 fb - 1 of 13 TeV proton–proton collision data collected by the ATLAS detector at the LHC. Events are selected by requiring exactly one isolated electron and one isolated muon with opposite charge and two or three jets, where exactly two jets are required to be b-tagged. For the selected events, measurements are presented for the charged-particle multiplicity, the scalar sum of the transverse momenta of the charged particles, and the same scalar sum in bins of charged-particle multiplicity. These observables are unfolded to the stable-particle level, thereby correcting for migration effects due to finite detector resolution, acceptance and efficiency effects. The particle-level measurements are compared with different colour reconnection models in Monte Carlo generators. These measurements disfavour some of the colour reconnection models and provide inputs to future optimisation of the parameters in Monte Carlo generators. © 2023, The Author(s).
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