| 1. |
- Aad, G., et al.
(författare)
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Measurement of the H→ γγ and H→ ZZ∗→ 4 ℓ cross-sections in pp collisions at √s=13.6 TeV with the ATLAS detector
- 2024
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Ingår i: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 84:1
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Tidskriftsartikel (refereegranskat)abstract
- The inclusive Higgs boson production cross-section is measured in the di-photon and the ZZ∗→ 4 ℓ decay channels using 31.4 and 29.0 fb - 1 of pp collision data respectively, collected with the ATLAS detector at a centre-of-mass energy of s=13.6 TeV . To reduce the model dependence, the measurement in each channel is restricted to a particle-level phase space that closely matches the channel’s detector-level kinematic selection, and it is corrected for detector effects. These measured fiducial cross-sections are σfid,γγ= 76-13+14 fb, and σfid,4ℓ= 2.80±0.74 fb, in agreement with the corresponding Standard Model predictions of 67.6 ± 3.7 fb and 3.67 ± 0.19 fb. Assuming Standard Model acceptances and branching fractions for the two channels, the fiducial measurements are extrapolated to the full phase space yielding total cross-sections of σ(pp→H)=67-11+12 pb and 46 ± 12 pb at 13.6 TeV from the di-photon and ZZ∗→ 4 ℓ measurements respectively. The two measurements are combined into a total cross-section measurement of σ(pp→ H) = 58.2 ± 8.7 pb, to be compared with the Standard Model prediction of σ(pp→ H) SM= 59.9 ± 2.6 pb.
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| 2. |
- Aad, G., et al.
(författare)
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Search for a new scalar resonance in flavour-changing neutral-current top-quark decays t †-> qX (q = u, c), with X ->†’ b(b)over-bar, in proton-proton collisions at root ˆšs=13 TeV with the ATLAS detector
- 2023
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479.
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Tidskriftsartikel (refereegranskat)abstract
- A search for flavour-changing neutral-current decays of a top quark into an up-type quark (either up or charm) and a light scalar particle X decaying into a bottom anti-bottom quark pair is presented. The search focuses on top-quark pair production where one top quark decays to qX, with X -> b (b) over bar, and the other top quark decays according to the Standard Model, with the W boson decaying leptonically. The final state is thus characterised by an isolated electron or muon and at least four jets. Events are categorised according to the multiplicity of jets and jets tagged as originating from b-quarks, and a neural network is used to discriminate between signal and background processes. The data analysed correspond to 139 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13TeV, recorded with the ATLAS detector at the LHC. The 95% confidence-level upper limits between 0.019% and 0.062% are derived for the branching fraction B(t -> uX) and between 0.018% and 0.078% for the branching fraction B(t -> cX), for masses of the scalar particle X between 20 and 160 GeV.
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| 3. |
- Aad, G., et al.
(författare)
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Search for New Phenomena in Two-Body Invariant Mass Distributions Using Unsupervised Machine Learning for Anomaly Detection at √s = 13 TeV with the ATLAS Detector
- 2024
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Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 132:8
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Tidskriftsartikel (refereegranskat)abstract
- Searches for new resonances are performed using an unsupervised anomaly-detection technique. Events with at least one electron or muon are selected from 140 fb−1 of pp collisions at √s ¼ 13 TeV recorded by ATLAS at the Large Hadron Collider. The approach involves training an autoencoder on data, and subsequently defining anomalous regions based on the reconstruction loss of the decoder. Studies focus on nine invariant mass spectra that contain pairs of objects consisting of one light jet or b jet and either one lepton (e; μ), photon, or second light jet or b jet in the anomalous regions. No significant deviations from the background hypotheses are observed. Limits on contributions from generic Gaussian signals with various widths of the resonance mass are obtained for nine invariant masses in the anomalous regions. © 2024 CERN, for the ATLAS Collaboration.
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| 4. |
- Aad, G., et al.
(författare)
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Search for top-philic heavy resonances in pp collisions at s=13 TeV with the ATLAS detector
- 2024
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Ingår i: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 84:2
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Tidskriftsartikel (refereegranskat)abstract
- A search for the associated production of a heavy resonance with a top-quark or a top-antitop-quark pair, and decaying into a tt¯ pair is presented. The search uses the data recorded by the ATLAS detector in pp collisions at s=13 TeV at the Large Hadron Collider during the years 2015–2018, corresponding to an integrated luminosity of 139 fb-1. Events containing exactly one electron or muon are selected. The two hadronically decaying top quarks from the resonance decay are reconstructed using jets clustered with a large radius parameter of R=1. The invariant mass spectrum of the two top quark candidates is used to search for a resonance signal in the range of 1.0 TeV to 3.2 TeV. The presence of a signal is examined using an approach with minimal model dependence followed by a model-dependent interpretation. No significant excess is observed over the background expectation. Upper limits on the production cross section times branching ratio at 95% confidence level are provided for a heavy Z′ boson based on a simplified model, for Z′ mass between 1.0 TeV and 3.0 TeV. The observed (expected) limits range from 21 (14) fb to 119 (86) fb depending on the choice of model parameters. © The Author(s) 2024.
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| 5. |
- Aad, G., et al.
(författare)
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Study of Z→llγ decays at s = 8 TeV with the ATLAS detector
- 2024
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Ingår i: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 84:2
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study of Z→llγ decays with the ATLAS detector at the Large Hadron Collider. The analysis uses a proton–proton data sample corresponding to an integrated luminosity of 20.2 fb-1 collected at a centre-of-mass energy s = 8 TeV. Integrated fiducial cross-sections together with normalised differential fiducial cross-sections, sensitive to the kinematics of final-state QED radiation, are obtained. The results are found to be in agreement with state-of-the-art predictions for final-state QED radiation. First measurements of Z→llγγ decays are also reported. © The Author(s) 2024.
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| 6. |
- Mullier, Geoffrey A., et al.
(författare)
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Measurement of Suppression of Large-Radius Jets and Its Dependence on Substructure in Pb+Pb Collisions at √sNN=5.02 TeV with the ATLAS Detector
- 2023
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Ingår i: Physical Review Letters. - : American Physical Society (APS). - 1079-7114 .- 0031-9007. ; 131:17
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Tidskriftsartikel (refereegranskat)abstract
- This letter presents a measurement of the nuclear modification factor of large-radius jets in Formula Presented Formula Presented collisions by the ATLAS experiment. The measurement is performed using Formula Presented and Formula Presented of Formula Presented and Formula Presented data, respectively. The large-radius jets are reconstructed with the anti-Formula Presented algorithm using a radius parameter of Formula Presented, by reclustering anti-Formula Presented Formula Presented jets, and are measured over the transverse momentum (Formula Presented) kinematic range of Formula Presented and absolute pseudorapidity Formula Presented. The large-radius jet constituents are further reclustered using the Formula Presented algorithm in order to obtain the splitting parameters, Formula Presented and Formula Presented, which characterize the transverse momentum scale and angular separation for the hardest splitting in the jet, respectively. The nuclear modification factor, Formula Presented, obtained by comparing the Formula Presented jet yields to those in Formula Presented collisions, is measured as a function of jet transverse momentum (Formula Presented) and Formula Presented or Formula Presented. A significant difference in the quenching of large-radius jets having single subjet and those with more complex substructure is observed. Systematic comparison of jet suppression in terms of Formula Presented for different jet definitions is also provided. Presented results support the hypothesis that jets with hard internal splittings lose more energy through quenching and provide a new perspective for understanding the role of jet structure in jet suppression. © 2023 CERN, for the ATLAS Collaboration.
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| 7. |
- Mullier, Geoffrey A., et al.
(författare)
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Measurement of the charge asymmetry in top-quark pair production in association with a photon with the ATLAS experiment
- 2023
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 843
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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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| 8. |
- Mullier, Geoffrey A., et al.
(författare)
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Measurement of the cross-sections of the electroweak and total production of a Zγ pair in association with two jets in pp collisions at √ˆšs=13TeV with the ATLAS detector
- 2023
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Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 846
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Tidskriftsartikel (refereegranskat)abstract
- This Letter presents the measurement of the fiducial and differential cross-sections of the electroweakproduction of a Z γ pair in association with two jets. The analysis uses 140 fb−1 of LHC proton–protoncollision data taken at √s=13 TeV recorded by the ATLAS detector during the years 2015–2018. Eventswith a Z boson candidate decaying into either an e+e− or μ+μ− pair, a photon and two jets areselected. The electroweak component is extracted by requiring a large dijet invariant mass and by usingthe information about the centrality of the system and is measured with an observed and expectedsignificance well above five standard deviations. The fiducial pp → Z γ j j cross-section for the electroweakproduction is measured to be 3.6 ± 0.5 fb. The total fiducial cross-section that also includes contributionswhere the jets arise from strong interactions is measured to be 16.8+2.0−1.8 fb. The results are consistentwith the Standard Model predictions. Differential cross-sections are also measured using the same eventsand are compared with parton-shower Monte Carlo simulations. Good agreement is observed betweendata and predictions.
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| 9. |
- Mullier, G.A., et al.
(författare)
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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
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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, Geoffrey A., et al.
(författare)
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Measurement of the Higgs boson mass with H →†’ γγ decays in 140 fb-1 of √ˆšs=13 TeV pp collisions with the ATLAS detector
- 2023
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Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 847
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Tidskriftsartikel (refereegranskat)abstract
- The mass of the Higgs boson is measured in the H -> γγ decay channel, exploiting the high resolution of the invariant mass of photon pairs reconstructed from the decays of Higgs bosons produced in proton-proton collisions at a centre-of-mass energy √s = 13 TeV. The dataset was collected between 2015 and 2018 by the ATLAS detector at the Large Hadron Collider, and corresponds to an integrated luminosity of 140 fb-1. The measured value of the Higgs boson mass is 125.17 ± 0.11 (stat.) ± 0.09 (syst.) GeV and is based on an improved energy scale calibration for photons, whose impact on the measurement is about four times smaller than in the previous publication. A combination with the corresponding measurement using 7 and 8 TeV pp collision ATLAS data results in a Higgs boson mass measurement of 125.22 ± 0.11 (stat.) ± 0.09 (syst.) GeV. With an uncertainty of 1.1 per mille, this is currently the most precise measurement of the mass of the Higgs boson from a single decay channel.
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