| 1. |
- Aaboud, M., et al.
(författare)
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Measurement of the relative Bc± /B± production cross section with the ATLAS detector at s =8 TeV MEASUREMENT of the RELATIVE Bc± /B± ... AABOUD M. et al.
- 2021
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Ingår i: Physical Review D. - 2470-0010. ; 104:1
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Tidskriftsartikel (refereegranskat)abstract
- The total cross section and differential cross sections for the production of Bc± mesons, times their branching fraction to J/ψπ±, are measured relative to those for the production of B± mesons, times their branching fraction to J/ψK±. The data used for this study correspond to an integrated luminosity of 20.3 fb-1 of pp collisions recorded by the ATLAS detector at the Large Hadron Collider in 2012 at a center-of-mass energy of s=8 TeV. The measurement is performed differentially in bins of transverse momentum pT for 13 GeV22 GeV and in bins of rapidity y for |y|13 GeV and |y|
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| 2. |
- Aad, G., et al.
(författare)
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Measurement of the jet mass in high transverse momentum Z(→bb‾)γ production at s=13TeV using the ATLAS detector
- 2021
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 812
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Tidskriftsartikel (refereegranskat)abstract
- The integrated fiducial cross-section and unfolded differential jet mass spectrum of high transverse momentum Z→bb‾ decays are measured in Zγ events in proton–proton collisions at s=13TeV. The data analysed were collected between 2015 and 2016 with the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 36.1fb−1. Photons are required to have a transverse momentum pT>175GeV. The Z→bb‾ decay is reconstructed using a jet with pT>200GeV, found with the anti-kt R=1.0 jet algorithm, and groomed to remove soft and wide-angle radiation and to mitigate contributions from the underlying event and additional proton–proton collisions. Two different but related measurements are performed using two jet grooming definitions for reconstructing the Z→bb‾ decay: trimming and soft drop. These algorithms differ in their experimental and phenomenological implications regarding jet mass reconstruction and theoretical precision. To identify Z bosons, b-tagged R=0.2 track-jets matched to the groomed large-R calorimeter jet are used as a proxy for the b-quarks. The signal yield is determined from fits of the data-driven background templates to the different jet mass distributions for the two grooming methods. Integrated fiducial cross-sections and unfolded jet mass spectra for each grooming method are compared with leading-order theoretical predictions. The results are found to be in good agreement with Standard Model expectations within the current statistical and systematic uncertainties. © 2020 The Author
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| 3. |
- Andrean, Stefio Y., 1991-, et al.
(författare)
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Measurements of differential cross-sections in top-quark pair events with a high transverse momentum top quark and limits on beyond the Standard Model contributions to top-quark pair production with the ATLAS detector at √s=13 TeV
- 2022
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; :6
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Tidskriftsartikel (refereegranskat)abstract
- Cross-section measurements of top-quark pair production where the hadronically decaying top quark has transverse momentum greater than 355 GeV and the other top quark decays into ℓνb are presented using 139 fb−1 of data collected by the ATLAS experiment during proton-proton collisions at the LHC. The fiducial cross-section at √s = 13 TeV is measured to be σ = 1.267 ± 0.005 ± 0.053 pb, where the uncertainties reflect the limited number of data events and the systematic uncertainties, giving a total uncertainty of 4.2%. The cross-section is measured differentially as a function of variables characterising the tt¯ system and additional radiation in the events. The results are compared with various Monte Carlo generators, including comparisons where the generators are reweighted to match a parton-level calculation at next-to-next-to-leading order. The reweighting improves the agreement between data and theory. The measured distribution of the top-quark transverse momentum is used to search for new physics in the context of the effective field theory framework. No significant deviation from the Standard Model is observed and limits are set on the Wilson coefficients of the dimension-six operators OtG and O(8)tq, where the limits on the latter are the most stringent to date.
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| 4. |
- Andrean, Stefio Y., 1991-, et al.
(författare)
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Probing the CP nature of the top–Higgs Yukawa coupling in tt¯H??¯? and tH events with H→bb¯?→??¯ decays using the ATLAS detector at the LHC
- 2024
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Ingår i: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 849
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Tidskriftsartikel (refereegranskat)abstract
- The CP properties of the coupling between the Higgs boson and the top quark are investigated using 139 fb−1 of proton–proton collision data recorded by the ATLAS experiment at the LHC at a centre-of-mass energy of s√=13?=13 TeV. The CP structure of the top quark–Higgs boson Yukawa coupling is probed in events with a Higgs boson decaying into a pair of b-quarks and produced in association with either a pair of top quarks, tt¯H??¯?, or a single top quark, tH. Events containing one or two electrons or muons are used for the measurement. Multivariate techniques are used to select regions enriched in tt¯H??¯? and tH events, where dedicated CP-sensitive observables are exploited. In an extension of the Standard Model (SM) with a CP-odd admixture in the top–Higgs Yukawa coupling, the mixing angle between CP-even and CP-odd couplings is measured to be α=11∘+52∘−73∘?=11−73∘∘+52∘, compatible with the SM prediction corresponding to α=0?=0.
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| 5. |
- Andrean, Stefio Y., 1991-, et al.
(författare)
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Search for heavy particles in the b-tagged dijet mass distribution with additional b-tagged jets in proton-proton collisions at √s=13 TeV with the ATLAS experiment
- 2022
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Ingår i: Physical Review D. - : American Physical Society (APS). - 2470-0010 .- 2470-0029. ; 105:1
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Tidskriftsartikel (refereegranskat)abstract
- A search optimized for new heavy particles decaying to two b-quarks and produced in association with additional b-quarks is reported. The sensitivity is improved by b-tagging at least one lower-pT jet in addition to the two highest-pT jets. The data used in this search correspond to an integrated luminosity of 103 fb−1 collected with a dedicated trijet trigger during the 2017 and 2018 √s=13 TeV proton-proton collision runs with the ATLAS detector at the LHC. The search looks for resonant peaks in the b-tagged dijet invariant mass spectrum over a smoothly falling background. The background is estimated with an innovative data-driven method based on orthonormal functions. The observed b-tagged dijet invariant mass spectrum is compatible with the background-only hypothesis. Upper limits at 95% confidence level on a heavy vector-boson production cross section times branching ratio to a pair of b-quarks are derived.
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| 6. |
- Andrean, Stefio Y., 1991-, et al.
(författare)
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Search for single production of a vectorlike T quark decaying into a Higgs boson and top quark with fully hadronic final states using the ATLAS detector
- 2022
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Ingår i: Physical Review D. - : American Physical Society (APS). - 2470-0010 .- 2470-0029. ; 105:9
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Tidskriftsartikel (refereegranskat)abstract
- A search is made for a vectorlike T quark decaying into a Higgs boson and a top quark in 13 TeV proton-proton collisions using the ATLAS detector at the Large Hadron Collider with a data sample corresponding to an integrated luminosity of 139 fb−1. The Higgs-boson and top-quark candidates are identified in the all-hadronic decay mode, where H → bb¯ and t → bW → bqq¯′ are reconstructed as large-radius jets. The candidate Higgs boson, top quark, and associated B hadrons are identified using tagging algorithms. No significant excess is observed above the background, so limits are set on the production cross section of a singlet T quark at 95% confidence level, depending on the mass mT and coupling κT of the vectorlike T quark to Standard Model particles. In the considered mass range between 1.0 and 2.3 TeV, the upper limiton the allowed coupling values increases with mT from a minimum value of 0.35 for 1.07 < mT < 1.4 TeV to 1.6 for mT=2.3 TeV.
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| 7. |
- Mullier, G.A., et al.
(författare)
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A search for an unexpected asymmetry in the production of e+μ− and e−μ+ pairs in proton–proton collisions recorded by the ATLAS detector at √s = 13 TeV
- 2022
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 830
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Tidskriftsartikel (refereegranskat)abstract
- This search, a type not previously performed at ATLAS, uses a comparison of the production cross sections for e+μ− and e−μ+ pairs to constrain physics processes beyond the Standard Model. It uses 139fb−1 of proton–proton collision data recorded at √s=13 TeV at the LHC. Targeting sources of new physics which prefer final states containing e+μ− to e−μ+, the search contains two broad signal regions which are used to provide model-independent constraints on the ratio of cross sections at the 2% level. The search also has two special selections targeting supersymmetric models and leptoquark signatures. Observations using one of these selections are able to exclude, at 95% confidence level, singly produced smuons with masses up to 640 GeV in a model in which the only other light sparticle is a neutralino when the R-parity-violating coupling λ231′ is close to unity. Observations using the other selection exclude scalar leptoquarks with masses below 1880 GeV when geu1R=gμc1R=1, at 95% confidence level. The limit on the coupling reduces to geu1R=gμc1R=0.46 for a mass of 1420 GeV.
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| 8. |
- Mullier, G.A., et al.
(författare)
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A search for the dimuon decay of the Standard Model Higgs boson with the ATLAS detector
- 2021
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 812
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Tidskriftsartikel (refereegranskat)abstract
- A search for the dimuon decay of the Standard Model (SM) Higgs boson is performed using data corresponding to an integrated luminosity of 139 fb−1 collected with the ATLAS detector in Run 2 pp collisions at s=13 TeV at the Large Hadron Collider. The observed (expected) significance over the background-only hypothesis for a Higgs boson with a mass of 125.09 GeV is 2.0σ (1.7σ). The observed upper limit on the cross section times branching ratio for pp→H→μμ is 2.2 times the SM prediction at 95% confidence level, while the expected limit on a H→μμ signal assuming the absence (presence) of a SM signal is 1.1 (2.0). The best-fit value of the signal strength parameter, defined as the ratio of the observed signal yield to the one expected in the SM, is μ=1.2±0.6. © 2020 The Author(s)
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| 9. |
- Mullier, G.A., et al.
(författare)
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AtlFast3 : The Next Generation of Fast Simulation in ATLAS
- 2022
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Ingår i: Computing and Software for Big Science. - : Springer Science and Business Media LLC. - 2510-2044 .- 2510-2036. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- The ATLAS experiment at the Large Hadron Collider has a broad physics programme ranging from precision measurements to direct searches for new particles and new interactions, requiring ever larger and ever more accurate datasets of simulated Monte Carlo events. Detector simulation with GEANT4 is accurate but requires significant CPU resources. Over the past decade, ATLAS has developed and utilized tools that replace the most CPU-intensive component of the simulation—the calorimeter shower simulation—with faster simulation methods. Here, AtlFast3, the next generation of high-accuracy fast simulation in ATLAS, is introduced. AtlFast3 combines parameterized approaches with machine-learning techniques and is deployed to meet current and future computing challenges, and simulation needs of the ATLAS experiment. With highly accurate performance and significantly improved modelling of substructure within jets, AtlFast3 can simulate large numbers of events for a wide range of physics processes.
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| 10. |
- Mullier, G.A., et al.
(författare)
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Constraints on Higgs boson production with large transverse momentum using H →b b ¯ decays in the ATLAS detector
- 2022
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Ingår i: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 105:9
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports constraints on Higgs boson production with transverse momentum above 1 TeV. The analyzed data from proton-proton collisions at a center-of-mass energy of 13 TeV were recorded with the ATLAS detector at the Large Hadron Collider from 2015 to 2018 and correspond to an integrated luminosity of 136 fb-1. Higgs bosons decaying into bb¯ are reconstructed as single large-radius jets recoiling against a hadronic system and are identified by the experimental signature of two b-hadron decays. The experimental techniques are validated in the same kinematic regime using the Z→bb¯ process. The 95% confidence-level upper limit on the cross section for Higgs boson production with transverse momentum above 450 GeV is 115 fb, and above 1 TeV it is 9.6 fb. The Standard Model cross section predictions for a Higgs boson with a mass of 125 GeV in the same kinematic regions are 18.4 fb and 0.13 fb, respectively. © 2022 CERN.
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