| 1. |
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- 2019
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Journal article (peer-reviewed)
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| 2. |
- Tremblay, Mark S, et al.
(author)
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Sedentary Behavior Research Network (SBRN) - Terminology Consensus Project process and outcome.
- 2017
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In: The international journal of behavioral nutrition and physical activity. - : Springer Science and Business Media LLC. - 1479-5868. ; 14:1
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Journal article (peer-reviewed)abstract
- The prominence of sedentary behavior research in health science has grown rapidly. With this growth there is increasing urgency for clear, common and accepted terminology and definitions. Such standardization is difficult to achieve, especially across multi-disciplinary researchers, practitioners, and industries. The Sedentary Behavior Research Network (SBRN) undertook a Terminology Consensus Project to address this need.First, a literature review was completed to identify key terms in sedentary behavior research. These key terms were then reviewed and modified by a Steering Committee formed by SBRN. Next, SBRN members were invited to contribute to this project and interested participants reviewed and provided feedback on the proposed list of terms and draft definitions through an online survey. Finally, a conceptual model and consensus definitions (including caveats and examples for all age groups and functional abilities) were finalized based on the feedback received from the 87 SBRN member participants who responded to the original invitation and survey.Consensus definitions for the terms physical inactivity, stationary behavior, sedentary behavior, standing, screen time, non-screen-based sedentary time, sitting, reclining, lying, sedentary behavior pattern, as well as how the terms bouts, breaks, and interruptions should be used in this context are provided.It is hoped that the definitions resulting from this comprehensive, transparent, and broad-based participatory process will result in standardized terminology that is widely supported and adopted, thereby advancing future research, interventions, policies, and practices related to sedentary behaviors.
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| 3. |
- Augenstein, Karoline, et al.
(author)
-
Five priorities to advance transformative transdisciplinary research
- 2024
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In: Current Opinion in Environmental Sustainability. - 1877-3435 .- 1877-3443. ; 68
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Research review (peer-reviewed)abstract
- In response to the climate and biodiversity crisis, the number of transdisciplinary research projects in which researchers partner with sustainability initiatives to foster transformative change is increasing globally. To enable and catalyze substantial transformative change, transformative transdisciplinary research (TTDR) is urgently needed to provide knowledge and guidance for actions. We review prominent discussions on TTDR and draw on our experiences from research projects in the Global South and North. Drawing on this, we identify key gaps and stimulate debate on how sustainability researchers can enable and catalyze transformative change by advancing five priority areas: clarify what TTDR is, conduct meaningful people-centric research, unpack how to act at deep leverage points, improve engagement with diverse knowledge systems, and explore potentials and risks of global digitalization for transformative change.
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| 4. |
- Backman, Filip, 1991-, et al.
(author)
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Charged-hadron production in pp, p plus Pb, Pb plus Pb, and Xe plus Xe collisions at √sNN=5 TeV with the ATLAS detector at the LHC
- 2023
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In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; :7
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Journal article (peer-reviewed)abstract
- This paper presents measurements of charged-hadron spectra obtained in pp, p+Pb, and Pb+Pb collisions at √s or √sNN = 5.02 TeV, and in Xe+Xe collisions at √sNN = 5.44 TeV. The data recorded by the ATLAS detector at the LHC have total integrated luminosities of 25 pb−1, 28 nb−1, 0.50 nb−1, and 3 μb−1, respectively. The nuclear modification factors RpPb and RAA are obtained by comparing the spectra in heavy-ion and pp collisions in a wide range of charged-particle transverse momenta and pseudorapidity. The nuclear modification factor RpPb shows a moderate enhancement above unity with a maximum at pT ≈ 3 GeV; the enhancement is stronger in the Pb-going direction. The nuclear modification factors in both Pb+Pb and Xe+Xe collisions feature a significant, centrality-dependent suppression. They show a similar distinct pT-dependence with a local maximum at pT ≈ 2 GeV and a local minimum at pT ≈ 7 GeV. This dependence is more distinguishable in more central collisions. No significant |η|-dependence is found. A comprehensive comparison with several theoretical predictions is also provided. They typically describe RAA better in central collisions and in the pT range from about 10 to 100 GeV.
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| 5. |
- Pereira, Laura M., 1985-, et al.
(author)
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Equity and justice should underpin the discourse on tipping points
- 2024
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In: Earth System Dynamics. - 2190-4979 .- 2190-4987. ; 15:2, s. 341-366
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Research review (peer-reviewed)abstract
- Radical and quick transformations towards sustainability will be fundamental to achieving a more sustainable future. However, deliberate interventions to reconfigure systems will result in winners and losers, with the potential for greater or lesser equity and justice outcomes. Positive tipping points (PTPs) have been proposed as interventions in complex systems with the aim to (a) reduce the likelihood of negative Earth system tipping points and/or (b) increase the likelihood of achieving just social foundations. However, many narratives around PTPs often do not take into account the entire spectrum of impacts the proposed alternatives could have or still rely on narratives that maintain current unsustainable behaviours and marginalize many people (i.e. do not take “b” into account). One such example is the move from petrol-based to electric vehicles. An energy transition that remains based on natural resource inputs from the Global South must be unpacked with an equity and justice lens to understand the true cost of this transition. There are two arguments why a critical engagement with these and other similar proposals needs to be made. First, the idea of transitioning through a substitution (e.g. of fuel) while maintaining the system structure (e.g. of private vehicles) may not necessarily be conceived as the kind of radical transformation being called for by global scientific bodies like the Intergovernmental Panel on Climate Change (IPCC) and Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES). Second, and probably more importantly, the question of positive for whom, positive where, and positive how must be considered. In this paper, we unpack these narratives using a critical decolonial view from the south and outline their implications for the concept of tipping points.
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| 6. |
- Aad, G., et al.
(author)
-
A search for heavy Higgs bosons decaying into vector bosons in same-sign two-lepton final states in pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Journal article (peer-reviewed)abstract
- A search for heavy Higgs bosons produced in association with a vector boson and decaying into a pair of vector bosons is performed in final states with two leptons (electrons or muons) of the same electric charge, missing transverse momentum and jets. A data sample of proton–proton collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018 is used. The data correspond to a total integrated luminosity of 139 fb−1. The observed data are in agreement with Standard Model background expectations. The results are interpreted using higher-dimensional operators in an effective field theory. Upper limits on the production cross-section are calculated at 95% confidence level as a function of the heavy Higgs boson’s mass and coupling strengths to vector bosons. Limits are set in the Higgs boson mass range from 300 to 1500 GeV, and depend on the assumed couplings. The highest excluded mass for a heavy Higgs boson with the coupling combinations explored is 900 GeV. Limits on coupling strengths are also provided.
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| 7. |
- Aad, G., et al.
(author)
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Combination of inclusive top-quark pair production cross-section measurements using ATLAS and CMS data at √s=7 and 8 TeV
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Journal article (peer-reviewed)abstract
- A combination of measurements of the inclusive top-quark pair production cross-section performed by ATLAS and CMS in proton–proton collisions at centre-of-mass energies of 7 and 8 TeV at the LHC is presented. The cross-sections are obtained using top-quark pair decays with an opposite-charge electron–muon pair in the final state and with data corresponding to an integrated luminosity of about 5 fb−1 at √s = 7 TeV and about 20 fb−1 at √s = 8 TeV for each experiment. The combined cross-sections are determined to be 178.5 ± 4.7 pb at √s = 7 TeV and pb at √s = 8 TeV with a correlation of 0.41, using a reference top-quark mass value of 172.5 GeV. The ratio of the combined cross-sections is determined to be R8/7 = 1.363 ± 0.032. The combined measured cross-sections and their ratio agree well with theory calculations using several parton distribution function (PDF) sets. The values of the top-quark pole mass (with the strong coupling fixed at 0.118) and the strong coupling (with the top-quark pole mass fixed at 172.5 GeV) are extracted from the combined results by fitting a next-to-next-to-leading-order plus next-to-next-to-leading-log QCD prediction to the measurements. Using a version of the NNPDF3.1 PDF set containing no top-quark measurements, the results obtained are = GeV and αs(mZ)=.
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| 8. |
- Aad, G., et al.
(author)
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Combination of searches for invisible decays of the Higgs boson using 139 fb−1 of proton-proton collision data at √s=13 TeV collected with the ATLAS experiment
- 2023
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 842
-
Journal article (peer-reviewed)abstract
- Many extensions of the Standard Model predict the production of dark matter particles at the LHC. Sufficiently light dark matter particles may be produced in decays of the Higgs boson that would appear invisible to the detector. This Letter presents a statistical combination of searches for H→invisible decays where multiple production modes of the Standard Model Higgs boson are considered. These searches are performed with the ATLAS detector using 139 fb−1 of proton–proton collisions at a centre–of–mass energy of at the LHC. In combination with the results at √s=7TeV and 8TeV, an upper limit on the H→invisible branching ratio of 0.107 (0.077) at the 95% confidence level is observed (expected). These results are also interpreted in the context of models where the 125 GeV Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross-section of weakly interacting massive particles and nucleons.
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| 9. |
- Aad, G., et al.
(author)
-
Constraints on the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using pp collisions at √s=13 TeV
- 2023
-
In: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 843
-
Journal article (peer-reviewed)abstract
- Constraints on the Higgs boson self-coupling are set by combining double-Higgs boson analyses in the b¯bb¯b, b¯bτ +τ − and b¯bγγ decay channels with single-Higgs boson analyses targeting the γγ , Z Z∗, W W ∗, τ +τ − and b¯b decay channels. The data used in these analyses were recorded by the ATLAS detector at the LHC in proton–proton collisions at √s = 13 TeV and correspond to an integrated luminosity of 126–139 fb−1. The combination of the double-Higgs analyses sets an upper limit of μH H < 2.4 at 95% confidence level on the double-Higgs production cross-section normalised to its Standard Model prediction. Combining the single-Higgs and double-Higgs analyses, with the assumption that new physics affects only the Higgs boson self-coupling (λHHH ), values outside the interval −0.4 < κλ = (λHHH /λ ) < 6.3 are excluded at 95% confidence level. The combined single-Higgs and double-Higgs analyses provide results with fewer assumptions, by adding in the fit more coupling modifiers introduced to account for the Higgs boson interactions with the other Standard Model particles. In this relaxed scenario, the constraint becomes −1.4 < κλ < 6.1 at 95% CL
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| 10. |
- Aad, G., et al.
(author)
-
Correlations between flow and transverse momentum in Xe+Xe and Pb+Pb collisions at the LHC with the ATLAS detector : A probe of the heavy-ion initial state and nuclear deformation
- 2023
-
In: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 107:5
-
Journal article (peer-reviewed)abstract
- The correlations between flow harmonics vn for n=2, 3, and 4 and mean transverse momentum [pT] in 129Xe+129Xe and 208Pb+208Pb collisions at √s=5.44 and 5.02 TeV, respectively, are measured using charged particles with the ATLAS detector. The correlations are potentially sensitive to the shape and size of the initial geometry, nuclear deformation, and initial momentum anisotropy. The effects from nonflow and centrality fluctuations are minimized, respectively, via a subevent cumulant method and an event-activity selection based on particle production at very forward rapidity. The vn−[pT] correlations show strong dependencies on centrality, harmonic number n, pT, and pseudorapidity range. Current models qualitatively describe the overall centrality- and system-dependent trends but fail to quantitatively reproduce all features of the data. In central collisions, where models generally show good agreement, the v2−[pT] correlations are sensitive to the triaxiality of the quadruple deformation. Comparison of the model with the Pb+Pb and Xe+Xe data confirms that the 129Xe nucleus is a highly deformed triaxial ellipsoid that has neither a prolate nor oblate shape. This provides strong evidence for a triaxial deformation of the 129Xe nucleus from high-energy heavy-ion collisions.
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| 11. |
- Aad, G., et al.
(author)
-
Measurement of the CP properties of Higgs boson interactions with τ-leptons with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 83:7
-
Journal article (peer-reviewed)abstract
- A study of the charge conjugation and parity (CP) properties of the interaction between the Higgs boson and τ-leptons is presented. The study is based on a measurement of CP-sensitive angular observables defined by the visible decay products of τ-leptons produced in Higgs boson decays. The analysis uses 139 fb−1 of proton–proton collision data recorded at a centre-of-mass energy of √s=13 TeV with the ATLAS detector at the Large Hadron Collider. Contributions from CP-violating interactions between the Higgs boson and τ-leptons are described by a single mixing angle parameter φτ in the generalised Yukawa interaction. Without constraining the H→ττ signal strength to its expected value under the Standard Model hypothesis, the mixing angle φτ is measured to be 9°±16°, with an expected value of 0°±28° at the 68% confidence level. The pure CP-odd hypothesis is disfavoured at a level of 3.4 standard deviations. The results are compatible with the predictions for the Higgs boson in the Standard Model.
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| 12. |
- Aad, G., et al.
(author)
-
Measurement of the production of a W boson in association with a charmed hadron in pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 108:3
-
Journal article (peer-reviewed)abstract
- The production of a W boson in association with a single charm quark is studied using 140 fb−1 of √s=13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. The charm quark is tagged by the presence of a charmed hadron reconstructed with a secondary-vertex fit. The W boson is reconstructed from the decay to either an electron or a muon and the missing transverse momentum present in the event. The charmed mesons reconstructed are D+→K−π+π+ and D*+→D0π+→(K−π+)π+ and the charge conjugate decays in the fiducial regions where pT(e,μ)>30 GeV, |η(e,μ)|<2.5, pT(D(*))>8 GeV, and |η(D(*))|<2.2. The integrated and normalized differential cross sections as a function of the pseudorapidity of the lepton from the W boson decay, and of the transverse momentum of the charmed hadron, are extracted from the data using a profile likelihood fit. The measured total fiducial cross sections are Results are compared with the predictions of next-to-leading-order quantum chromodynamics calculations performed using state-of-the-art parton distribution functions. Additionally, the ratio of charm to anticharm production cross sections is studied to probe the quark asymmetry. The ratio is found to be . The ratio and cross-section measurements are consistent with the predictions obtained with parton distribution function sets that have a symmetric sea, indicating that any asymmetry in the Bjorken-x region relevant for this measurement is small.
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| 13. |
- Aad, G., et al.
(author)
-
Measurements of differential cross sections of Higgs boson production through gluon fusion in the H → WW*→ eνμν final state at √s=13 TeV with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 83:9
-
Journal article (peer-reviewed)abstract
- Higgs boson production via gluon–gluon fusion is measured in the WW*→eνμν decay channel. The dataset utilized corresponds to an integrated luminosity of 139 fb−1 collected by the ATLAS detector from √s=13 TeV proton–proton collisions delivered by the Large Hadron Collider between 2015 and 2018. Differential cross sections are measured in a fiducial phase space restricted to the production of at most one additional jet. The results are consistent with Standard Model expectations, derived using different Monte Carlo generators.
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| 14. |
- Aad, G., et al.
(author)
-
Measurements of the suppression and correlations of dijets in Pb+Pb collisions at √sNN=5.02 TeV
- 2023
-
In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 107:5
-
Journal article (peer-reviewed)abstract
- Studies of the correlations of the two highest transverse momentum (leading) jets in individual Pb+Pb collision events can provide information about the mechanism of jet quenching by the hot and dense matter created in such collisions. In Pb+Pb and pp collisions at √sNN=5.02TeV, measurements of the leading dijet transverse momentum (pT) correlations are presented. Additionally, measurements in Pb+Pb collisions of the dijet pair nuclear modification factors projected along leading and subleading jet pT are made. The measurements are performed using the ATLAS detector at the LHC with 260 pb−1 of pp data collected in 2017 and 2.2 nb−1 of Pb+Pb data collected in 2015 and 2018. An unfolding procedure is applied to the two-dimensional leading and subleading jet pT distributions to account for experimental effects in the measurement of both jets. Results are provided for dijets with leading jet pT greater than 100 GeV. Measurements of the dijet-yield-normalized xJ distributions in Pb+Pb collisions show an increased fraction of imbalanced jets compared to pp collisions; these measurements are in agreement with previous measurements of the same quantity at 2.76 TeV in the overlapping kinematic range. Measurements of the absolutely normalized dijet rate in Pb+Pb and pp collisions are also presented, and show that balanced dijets are significantly more suppressed than imbalanced dijets in Pb+Pb collisions. It is observed in the measurements of the pair nuclear modification factors that the subleading jets are significantly suppressed relative to leading jets with pT between 100 and 316 GeV for all centralities in Pb+Pb collisions
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| 15. |
- Aad, G., et al.
(author)
-
Measurements of Zγ+jets differential cross sections in pp collisions at √s = 13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Journal article (peer-reviewed)abstract
- Differential cross-section measurements of Zγ production in association with hadronic jets are presented, using the full 139 fb−1 dataset of √s = 13 TeV proton–proton collisions collected by the ATLAS detector during Run 2 of the LHC. Distributions are measured using events in which the Z boson decays leptonically and the photon is usually radiated from an initial-state quark. Measurements are made in both one and two observables, including those sensitive to the hard scattering in the event and others which probe additional soft and collinear radiation. Different Standard Model predictions, from both parton-shower Monte Carlo simulation and fixed-order QCD calculations, are compared with the measurements. In general, good agreement is observed between data and predictions from MATRIX and MiNNLOPS, as well as next-to-leading-order predictions from MADGRAPH5_AMC@NLO and SHERPA.
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| 16. |
- Aad, G., et al.
(author)
-
Observation of electroweak production of two jets and a Z-boson pair
- 2023
-
In: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481. ; 19:2, s. 237-253
-
Journal article (peer-reviewed)abstract
- Electroweak symmetry breaking explains the origin of the masses of elementary particles through their interactions with the Higgs field. Besides the measurements of the Higgs boson properties, the study of the scattering of massive vector bosons with spin 1 allows the nature of electroweak symmetry breaking to be probed. Among all processes related to vector-boson scattering, the electroweak production of two jets and a Z-boson pair is a rare and important one. Here we report the observation of this process from proton–proton collision data corresponding to an integrated luminosity of 139 fb−1 recorded at a centre-of-mass energy of 13 TeV with the ATLAS detector at the Large Hadron Collider. We consider two different final states originating from the decays of the Z-boson pair: one containing four charged leptons and another containing two charged leptons and two neutrinos. The hypothesis of no electroweak production is rejected with a statistical significance of 5.7σ, and the measured cross-section for electroweak production is consistent with the Standard Model prediction. In addition, we report cross-sections for inclusive production of a Z-boson pair and two jets for the two final states.
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| 17. |
- Aad, G., et al.
(author)
-
Observation of four-top-quark production in the multilepton final state with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:6
-
Journal article (peer-reviewed)abstract
- This paper presents the observation of four-top-quark () production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity of 140 fb−1 at a centre-of-mass energy of 13 TeV collected using the ATLAS detector. Events containing two leptons with the same electric charge or at least three leptons (electrons or muons) are selected. Event kinematics are used to separate signal from background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The observed (expected) significance of the measured signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The production cross section is measured to be fb, consistent with the SM prediction of 12.0±2.4 fb within 1.8 standard deviations. Data are also used to set limits on the three-top-quark production cross section, being an irreducible background not measured previously, and to constrain the top-Higgs Yukawa coupling and effective field theory operator coefficients that affect production.
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| 18. |
- Aad, G., et al.
(author)
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Observation of Single-Top-Quark Production in Association with a Photon Using the ATLAS Detector
- 2023
-
In: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 131:18
-
Journal article (peer-reviewed)abstract
- This Letter reports the observation of single top quarks produced together with a photon, which directly probes the electroweak coupling of the top quark. The analysis uses 139 fb−1 of 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. Requiring a photon with transverse momentum larger than 20 GeV and within the detector acceptance, the fiducial cross section is measured to be 688±23(stat) , to be compared with the standard model prediction of at next-to-leading order in QCD.
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| 19. |
- Aad, G., et al.
(author)
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Production of Υ(nS) mesons in Pb+Pb and pp collisions at 5.02 TeV
- 2023
-
In: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 107:5
-
Journal article (peer-reviewed)abstract
- A measurement of the production of vector bottomonium states, Υ(1S), Υ(2S), and Υ(3S), in Pb+Pb and pp collisions at a center-of-mass energy per nucleon pair of 5.02 TeV is presented. The data correspond to integrated luminosities of 1.38nb−1 of Pb+Pb data collected in 2018, 0.44nb−1 of Pb+Pb data collected in 2015, and 0.26fb−1 of pp data collected in 2017 by the ATLAS detector at the Large Hadron Collider. The measurements are performed in the dimuon decay channel for transverse momentum <30GeV, absolute rapidity |yμμ|<1.5, and Pb+Pb event centrality 0–80%. The production rates of the three bottomonium states in Pb+Pb collisions are compared with those in pp collisions to extract the nuclear modification factors as functions of event centrality, , and |yμμ|. In addition, the suppression of the excited states relative to the ground state is studied. The results are compared with theoretical model calculations.
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| 20. |
- Aad, G., et al.
(author)
-
Search for a light charged Higgs boson in t → H±b decays, with H± → cb, in the lepton plus jets final state in proton-proton collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:9
-
Journal article (peer-reviewed)abstract
- A search for a charged Higgs boson, H±, produced in top-quark decays, t → H±b, is presented. The search targets H± decays into a bottom and a charm quark, H± → cb. The analysis focuses on a selection enriched in top-quark pair production, where one top quark decays into a leptonically decaying W boson and a bottom quark, and the other top quark decays into a charged Higgs boson and a bottom quark. This topology leads to a lepton-plus-jets final state, characterised by an isolated electron or muon and at least four jets. The search exploits the high multiplicity of jets containing b-hadrons, and deploys a neural network classifier that uses the kinematic differences between the signal and the background. The search uses a dataset of proton-proton collisions collected at a centre-of-mass energy √s = 13 TeV between 2015 and 2018 with the ATLAS detector at CERN’s Large Hadron Collider, amounting to an integrated luminosity of 139 fb−1. Observed (expected) 95% confidence-level upper limits between 0.15% (0.09%) and 0.42% (0.25%) are derived for the product of branching fractions for charged Higgs boson masses between 60 and 160 GeV, assuming the SM production of the top-quark pairs.
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| 21. |
- Aad, G., et al.
(author)
-
Search for dark matter produced in association with a single top quark and an energetic W boson in √s=13 TeV pp collisions with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 83:7
-
Journal article (peer-reviewed)abstract
- This paper presents a search for dark matter, χ, using events with a single top quark and an energetic W boson. The analysis is based on proton–proton collision data collected with the ATLAS experiment at √s= 13 TeV during LHC Run 2 (2015–2018), corresponding to an integrated luminosity of 139 fb−1. The search considers final states with zero or one charged lepton (electron or muon), at least one b-jet and large missing transverse momentum. In addition, a result from a previous search considering two-charged-lepton final states is included in the interpretation of the results. The data are found to be in good agreement with the Standard Model predictions and the results are interpreted in terms of 95% confidence-level exclusion limits in the context of a class of dark matter models involving an extended two-Higgs-doublet sector together with a pseudoscalar mediator particle. The search is particularly sensitive to on-shell production of the charged Higgs boson state, H±, arising from the two-Higgs-doublet mixing, and its semi-invisible decays via the mediator particle, a: H±→W±a(→χχ). Signal models with H± masses up to 1.5 TeV and a masses up to 350 GeV are excluded assuming a tan β value of 1. For masses of a of 150 (250) GeV, tan β values up to 2 are excluded for H± masses between 200 (400) GeV and 1.5 TeV. Signals with tan β values between 20 and 30 are excluded for H± masses between 500 and 800 GeV.
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| 22. |
- Aad, G., et al.
(author)
-
Search for dark photons from Higgs boson decays via ZH production with a photon plus missing transverse momentum signature from pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Journal article (peer-reviewed)abstract
- This paper describes a search for dark photons (γd) in proton-proton collisions at √s = 13 TeV at the Large Hadron Collider (LHC). The dark photons are searched for in the decay of Higgs bosons (H → γγd) produced through the ZH production mode. The transverse mass of the system, made of the photon and the missing transverse momentum from the non-interacting γd, presents a distinctive signature as it peaks near the Higgs boson mass. The results presented use the total Run-2 integrated luminosity of 139 fb−1 recorded by the ATLAS detector at the LHC. The dominant reducible background processes are estimated using data-driven techniques. A Boosted Decision Tree technique is adopted to enhance the sensitivity of the search. As no excess is observed with respect to the Standard Model prediction, an observed (expected) upper limit on the branching ratio BR(H → γγd) of 2.28% () is set at 95% CL for massless γd. For massive dark photons up to 40 GeV, the observed (expected) upper limits on BR(H → γγd) at 95% confidence level is found within the [2.19,2.52]% ([2.71,3.11]%) range
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| 23. |
- Aad, G., et al.
(author)
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Search for displaced photons produced in exotic decays of the Higgs boson using 13 TeV pp collisions with the ATLAS detector
- 2023
-
In: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 108:3
-
Journal article (peer-reviewed)abstract
- A search is performed for delayed and nonpointing photons originating from the displaced decay of a neutral long-lived particle (LLP). The analysis uses the full run 2 dataset of proton-proton collisions delivered by the LHC at a center-of-mass energy of √s=13 TeV between 2015 and 2018 and recorded by the ATLAS detector, corresponding to an integrated luminosity of 139 fb−1. The capabilities of the ATLAS electromagnetic calorimeter are exploited to precisely measure the arrival times and trajectories of photons. The results are interpreted in a scenario where the LLPs are pair produced in exotic decays of the 125 GeV Higgs boson, and each LLP subsequently decays into a photon and a particle that escapes direct detection, giving rise to missing transverse momentum. No significant excess is observed above the expectation due to Standard Model background processes. The results are used to set upper limits on the branching ratio of the exotic decay of the Higgs boson. A model-independent limit is also set on the production of photons with large values of displacement and time delay.
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| 24. |
- Aad, G., et al.
(author)
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Search for doubly charged Higgs boson production in multi-lepton final states using 139 fb-1 of proton-proton collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 83:7
-
Journal article (peer-reviewed)abstract
- A search for pair production of doubly charged Higgs bosons (H±±), each decaying into a pair of prompt, isolated, and highly energetic leptons with the same electric charge, is presented. The search uses a proton–proton collision data sample at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb−1 recorded by the ATLAS detector during Run 2 of the Large Hadron Collider (LHC). This analysis focuses on same-charge leptonic decays, H±±→ℓ±ℓ′± where ℓ,ℓ′=e,μ,τ, in two-, three-, and four-lepton channels, but only considers final states which include electrons or muons. No evidence of a signal is observed. Corresponding upper limits on the production cross-section of a doubly charged Higgs boson are derived, as a function of its mass m(H±±), at 95% confidence level. Assuming that the branching ratios to each of the possible leptonic final states are equal, , the observed (expected) lower limit on the mass of a doubly charged Higgs boson is 1080 GeV (1065 GeV) within the left-right symmetric type-II seesaw model, which is the strongest limit to date produced by the ATLAS Collaboration. Additionally, this paper provides the first direct test of the Zee–Babu neutrino mass model at the LHC, yielding an observed (expected) lower limit of m(H±±) = 900 GeV (880 GeV).
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| 25. |
- Aad, G., et al.
(author)
-
Search for flavour-changing neutral-current couplings between the top quark and the photon with the ATLAS detector at √s=13 TeV
- 2023
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 842
-
Journal article (peer-reviewed)abstract
- This letter documents a search for flavour-changing neutral currents (FCNCs), which are strongly suppressed in the Standard Model, in events with a photon and a top quark with the ATLAS detector. The analysis uses data collected in pp collisions at √s = 13 TeV during Run 2 of the LHC, corresponding to an integrated luminosity of 139 fb−1. Both FCNC top-quark production and decay are considered. The final state consists of a charged lepton, missing transverse momentum, a b-tagged jet, one high-momentum photon and possibly additional jets. A multiclass deep neural network is used to classify events either as signal in one of the two categories, FCNC production or decay, or as background. No significant excess of events over the background prediction is observed and 95% CL upper limits are placed on the strength of left- and right-handed FCNC interactions. The 95% CL bounds on the branching fractions for the FCNC top-quark decays, estimated (expected) from both top-quark production and decay, are B(t → uγ ) < 0.85 (0.88) × 10−5 and B(t → cγ ) < 4.2 (3.40) × 10−5 for a left-handed tqγ coupling, and B(t → uγ ) < 1.2 (1.20)×10−5 and B(t → cγ ) < 4.5 (3.70)×10−5 for a right-handed coupling.
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| 26. |
- Aad, G., et al.
(author)
-
Search for heavy long-lived multi-charged particles in the full LHC Run 2 pp collision data at √s=13 TeV using the ATLAS detector
- 2023
-
In: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 847
-
Journal article (peer-reviewed)abstract
- A search for heavy long-lived multi-charged particles is performed using the ATLAS detector at the LHC. Data collected in 2015-2018 at √s = 13 TeV from pp collisions corresponding to an integrated luminosity of 139 fb−1 are examined. Particles producing anomalously high ionization, consistent with long-lived spin-½ massive particles with electric charges from |q| = 2e to |q| = 7e are searched for. No statistically significant evidence of such particles is observed, and 95% confidence level cross-section upper limits are calculated and interpreted as the lower mass limits for a Drell-Yan plus photon-fusion production mode. The least stringent limit, 1060 GeV, is obtained for |q| = 2e particles, and the most stringent one, 1600 GeV, is for |q| = 6e particles.
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| 27. |
- Aad, G., et al.
(author)
-
Search for long-lived, massive particles in events with displaced vertices and multiple jets in pp collisions at √s = 13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:6
-
Journal article (peer-reviewed)abstract
- A search for long-lived particles decaying into hadrons is presented. The analysis uses 139 fb−1 of pp collision data collected at √s = 13 TeV by the ATLAS detector at the LHC using events that contain multiple energetic jets and a displaced vertex. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particles decaying in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are used to set limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and on scenarios with pair-production of supersymmetric particles with long-lived electroweakinos that decay via a small R-parity-violating coupling. The pair-production of electroweakinos with masses below 1.5 TeV is excluded for mean proper lifetimes in the range from 0.03 ns to 1 ns. When produced in the decay of m(g̃) = 2.4 TeV gluinos, electroweakinos with m() = 1.5 TeV are excluded with lifetimes in the range of 0.02 ns to 4 ns.
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| 28. |
- Aad, G., et al.
(author)
-
Search for pair-produced vector-like top and bottom partners in events with large missing transverse momentum in pp collisions with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:8
-
Journal article (peer-reviewed)abstract
- A search for pair-produced vector-like quarks using events with exactly one lepton (e or μ), at least four jets including at least one b-tagged jet, and large missing transverse momentum is presented. Data from proton–proton collisions at a centre-of-mass energy of √s=13 TeV, recorded by the ATLAS detector at the LHC from 2015 to 2018 and corresponding to an integrated luminosity of 139 fb−1, are analysed. Vector-like partners T and B of the top and bottom quarks are considered, as is a vector-like X with charge +5/3, assuming their decay into a W, Z, or Higgs boson and a third-generation quark. No significant deviations from the Standard Model expectation are observed. Upper limits on the production cross-section of T and B quark pairs as a function of their mass are derived for various decay branching ratio scenarios. The strongest lower limits on the masses are 1.59 TeV assuming mass-degenerate vector-like quarks and branching ratios corresponding to the weak-isospin doublet model, and 1.47 TeV (1.46 TeV) for exclusive T→Zt (B/X→Wt) decays. In addition, lower limits on the T and B quark masses are derived for all possible branching ratios.
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| 29. |
- Aad, G., et al.
(author)
-
Search for pair-production of vector-like quarks in pp collision events at √s = 13 TeV with at least one leptonically decaying Z boson and a third-generation quark with the ATLAS detector
- 2023
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 843
-
Journal article (peer-reviewed)abstract
- A search for the pair-production of vector-like quarks optimized for decays into a Z boson and a third-generation Standard Model quark is presented, using the full Run 2 dataset corresponding to 139 fb−1 of pp collisions at √s = 13 TeV, collected in 2015–2018 with the ATLAS detector at the Large Hadron Collider. The targeted final state is characterized by the presence of a Z boson with high transverse momentum, reconstructed from a pair of same-flavour leptons with opposite-sign charges, as well as by the presence of b-tagged jets and high-transverse-momentum large-radius jets reconstructed from calibrated smaller-radius jets. Events with exactly two or at least three leptons are used, which are further categorized by the presence of boosted W , Z, and Higgs bosons and top quarks. The categorization is performed using a neural-network-based boosted object tagger to enhance the sensitivity to signal relative to the background. No significant excess above the background expectation is observed and exclusion limits at 95% confidence level are set on the masses of the vector-like partners T and B of the top and bottom quarks, respectively. The limits depend on the branching ratio configurations and, in the case of 100% branching ratio for T → Zt and 100% branching ratio for B → Zb, this search sets the most stringent limits to date, allowing mT > 1.60 TeV and mB > 1.42 TeV, respectively.
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| 30. |
- Aad, G., et al.
(author)
-
Search for single vector-like B quark production and decay via B → bH(bb¯) in pp collisions at √s= 13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:11
-
Journal article (peer-reviewed)abstract
- A search is presented for single production of a vector-like B quark decaying into a Standard Model b-quark and a Standard Model Higgs boson, which decays into a pair. The search is carried out in 139 fb−1 of √s= 13 TeV proton-proton collision data collected by the ATLAS detector at the LHC between 2015 and 2018. No significant deviation from the Standard Model background prediction is observed, and mass-dependent exclusion limits at the 95% confidence level are set on the resonance production cross-section in several theoretical scenarios determined by the couplings cW, cZ and cH between the B quark and the Standard Model W, Z and Higgs bosons, respectively. For a vector-like B occurring as an isospin singlet, the search excludes values of cW greater than 0.45 for a B resonance mass (mB) between 1.0 and 1.2 TeV. For 1.2 TeV < mB < 2.0 TeV, cW values larger than 0.50–0.65 are excluded. If the B occurs as part of a (B, Y) doublet, the smallest excluded cZ coupling values range between 0.3 and 0.5 across the investigated resonance mass range 1.0 TeV < mB < 2.0 TeV.
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| 31. |
- Aad, G., et al.
(author)
-
Search for supersymmetry in final states with missing transverse momentum and three or more b-jets in 139 fb-1 of proton-proton collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 83:7
-
Journal article (peer-reviewed)abstract
- A search for supersymmetry involving the pair production of gluinos decaying via off-shell third-generation squarks into the lightest neutralino () is reported. It exploits LHC proton–proton collision data at a centre-of-mass energy √s=13 TeV with an integrated luminosity of 139 fb−1 collected with the ATLAS detector from 2015 to 2018. The search uses events containing large missing transverse momentum, up to one electron or muon, and several energetic jets, at least three of which must be identified as containing b-hadrons. Both a simple kinematic event selection and an event selection based upon a deep neural-network are used. No significant excess above the predicted background is found. In simplified models involving the pair production of gluinos that decay via off-shell top (bottom) squarks, gluino masses less than 2.44 TeV (2.35 TeV) are excluded at 95% CL for a massless . Limits are also set on the gluino mass in models with variable branching ratios for gluino decays to , and .
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| 32. |
- Aad, G., et al.
(author)
-
Search for the charged-lepton-flavor-violating decay Z→eμ in pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 108:3
-
Journal article (peer-reviewed)abstract
- A search for the charged-lepton-flavor-violating process Z→eμ is presented, using 139 fb−1 of √s=13 TeV pp collision data collected by the ATLAS experiment at the LHC. An excess in the eμ invariant mass spectrum near the Z boson mass would be a striking signature of new physics. No excess is observed, and an upper limit <2.62×10−7 is placed on the branching fraction at 95% confidence level, which is the most stringent limit to date.
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| 33. |
- Aad, G., et al.
(author)
-
Search in diphoton and dielectron final states for displaced production of Higgs or Z bosons with the ATLAS detector in √s=13 TeV pp collisions
- 2023
-
In: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 108:1
-
Journal article (peer-reviewed)abstract
- A search is presented for displaced production of Higgs bosons or Z bosons, originating from the decay of a neutral long-lived particle (LLP) and reconstructed in the decay modes H→γγ and Z→ee. The analysis uses the full Run 2 dataset of proton-proton collisions delivered by the LHC at an energy of √s=13 TeV between 2015 and 2018 and recorded by the ATLAS detector, corresponding to an integrated luminosity of 139 fb−1. Exploiting the capabilities of the ATLAS liquid argon calorimeter to precisely measure the arrival times and trajectories of electromagnetic objects, the analysis searches for the signature of pairs of photons or electrons which arise from a common displaced vertex and which arrive after some delay at the calorimeter. The results are interpreted in a gauge-mediated supersymmetry breaking model with pair-produced Higgsinos that decay to LLPs, and each LLP subsequently decays into either a Higgs boson or a Z boson. The final state includes at least two particles that escape direct detection, giving rise to missing transverse momentum. No significant excess is observed above the background expectation. The results are used to set upper limits on the cross section for Higgsino pair production, up to a mass of 369 (704) GeV for decays with 100% branching ratio of to Higgs (Z) bosons for a lifetime of 2 ns. A model-independent limit is also set on the production of pairs of photons or electrons with a significant delay in arrival at the calorimeter.
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| 34. |
- Andrean, Stefio Y., 1991-, et al.
(author)
-
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
-
In: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 849
-
Journal article (peer-reviewed)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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| 35. |
- Backman, Filip, 1991-, et al.
(author)
-
New techniques for jet calibration with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 83:8
-
Journal article (peer-reviewed)abstract
- A determination of the jet energy scale is presented using proton-proton collision data with a centre-of-mass energy of root s = 13 TeV, corresponding to an integrated luminosity of 140 fb(-1) collected using the ATLAS detector at the LHC. Jets are reconstructed using the ATLAS particle-flow method that combines charged-particle tracks and topo-clusters formed from energy deposits in the calorimeter cells. The anti-kt jet algorithm with radius parameter R = 0.4 is used to define the jet. Novel jet energy scale calibration strategies developed for the LHC Run 2 are reported that lay the foundation for the jet calibration in Run 3. Jets are calibrated with a series of simulation-based corrections, including state-of-the-art techniques in jet calibration such as machine learning methods and novel in situ calibrations to achieve better performance than the baseline calibration derived using up to 81 fb(-1) of Run 2 data. The performance of these new techniques is then examined in the in situ measurements by exploiting the transverse momentum balance between a jet and a reference object. The b-quark jet energy scale using particle flow jets is measured for the first time with around 1% precision using gamma+jet events.
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| 36. |
- Mullier, G.A., et al.
(author)
-
Cross-section measurements for the production of a Z boson in association with high-transverse-momentum jets in pp collisions at √s = 13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Science and Business Media Deutschland GmbH. - 1126-6708 .- 1029-8479. ; 2023:6
-
Journal article (peer-reviewed)abstract
- Cross-section measurements for a Z boson produced in association with high-transverse-momentum jets (pT ≥ 100 GeV) and decaying into a charged-lepton pair (e+e−, μ+μ−) are presented. The measurements are performed using proton–proton collisions at √s = 13 TeV corresponding to an integrated luminosity of 139 fb−1 collected by the ATLAS experiment at the LHC. Measurements of angular correlations between the Z boson and the closest jet are performed in events with at least one jet with pT ≥ 500 GeV. Event topologies of particular interest are the collinear emission of a Z boson in dijet events and a boosted Z boson recoiling against a jet. Fiducial cross sections are compared with state-of-the-art theoretical predictions. The data are found to agree with next-to-next-to-leading-order predictions by NNLOᴊᴇᴛ and with the next-to-leading-order multi-leg generators MADGRAPH5_AMC@NLO and SHERPA.
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| 37. |
- Mullier, G.A., et al.
(author)
-
Differential tt¯ cross-section measurements using boosted top quarks in the all-hadronic final state with 139 fb−1 of ATLAS data
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:4
-
Journal article (peer-reviewed)abstract
- Measurements of single-, double-, and triple-differential cross-sections are presented for boosted top-quark pair-production in 13 TeV proton–proton collisions recorded by the ATLAS detector at the LHC. The top quarks are observed through their hadronic decay and reconstructed as large-radius jets with the leading jet having transverse momentum (pT) greater than 500 GeV. The observed data are unfolded to remove detector effects. The particle-level cross-section, multiplied by the branching fraction and measured in a fiducial phase space defined by requiring the leading and second-leading jets to have pT > 500 GeV and pT > 350 GeV, respectively, is 331 ± 3(stat.) ± 39(syst.) fb. This is approximately 20% lower than the prediction of fb by POWHEG+PYTHIA 8 with next-to-leading-order (NLO) accuracy but consistent within the theoretical uncertainties. Results are also presented at the parton level, where the effects of top-quark decay, parton showering, and hadronization are removed such that they can be compared with fixed-order next-to-next-to-leading-order (NNLO) calculations. The parton-level cross-section, measured in a fiducial phase space similar to that at particle level, is 1.94 ± 0.02(stat.) ± 0.25(syst.) pb. This agrees with the NNLO prediction of pb. Reasonable agreement with the differential cross-sections is found for most NLO models, while the NNLO calculations are generally in better agreement with the data. The differential cross-sections are interpreted using a Standard Model effective field-theory formalism and limits are set on Wilson coefficients of several four-fermion operators.
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| 38. |
- Mullier, G.A., et al.
(author)
-
Exclusive dielectron production in ultraperipheral Pb+Pb collisions at √sNN=5.02 TeV with ATLAS
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:6
-
Journal article (peer-reviewed)abstract
- Exclusive production of dielectron pairs, γγ → e+e−, is studied using = 1.72 nb−1 of data from ultraperipheral collisions of lead nuclei at √sNN = 5.02 TeV recorded by the ATLAS detector at the LHC. The process of interest proceeds via photon–photon interactions in the strong electromagnetic fields of relativistic lead nuclei. Dielectron production is measured in the fiducial region defined by following requirements: electron transverse momentum > 2.5 GeV, absolute electron pseudorapidity |ηe| < 2.5, dielectron invariant mass mee > 5 GeV, and dielectron transverse momentum < 2 GeV. Differential cross-sections are measured as a function of mee, average , absolute dielectron rapidity |yee|, and scattering angle in the dielectron rest frame, |cos θ*|, in the inclusive sample, and also with a requirement of no activity in the forward direction. The total integrated fiducial cross-section is measured to be 215±1(stat.)(syst.)±4(lumi.) μb. Within experimental uncertainties the measured integrated cross-section is in good agreement with the QED predictions from the Monte Carlo programs STARLIGHT and SUPERCHIC, confirming the broad features of the initial photon fluxes. The differential cross-sections show systematic differences from these predictions which are more pronounced at high |yee| and |cos θ*| values.
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| 39. |
- Mullier, G.A., et al.
(author)
-
Measurement of cross sections for production of a Z boson in association with a flavor-inclusive or doubly b-tagged large-radius jet in proton-proton collisions at Formula Presented with the ATLAS experiment
- 2023
-
In: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 108:1
-
Journal article (peer-reviewed)abstract
- We present measurements of cross sections for production of a leptonically decaying Z boson in association with a large-radius jet in 13 TeV proton-proton collisions at the LHC, using 36 fb - 1 of data from the ATLAS detector. Integrated and differential cross sections are measured at particle level in both a flavor inclusive and a doubly b -tagged fiducial phase space. The large-radius jet mass and transverse momentum, its kinematic relationship to the Z boson, and the angular separation of b -tagged small-radius track jets within the large-radius jet are measured. This measurement constitutes an important test of perturbative quantum chromodynamics in kinematic and flavor configurations relevant to several Higgs boson and beyond-Standard-Model physics analyses. The results highlight issues with modeling of additional hadronic activity in the flavor-inclusive selection, and a distinction between flavor-number schemes in the b -tagged phase space. © 2023 CERN, for the ATLAS Collaboration.
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| 40. |
- Mullier, G.A., et al.
(author)
-
Measurement of muon pairs produced via ?? scattering in nonultraperipheral Pb+Pb collisions at √???=5.02 TeV with the ATLAS detector
- 2023
-
In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 107:5
-
Journal article (peer-reviewed)abstract
- Results of a measurement of dimuon photoproduction in nonultraperipheral Pb+Pb collisions at √???=5.02 TeV are presented. The measurement uses ATLAS data from the 2015 and 2018 Pb+Pb data-taking periods at the LHC with an integrated luminosity of 1.94nb−1. The ??→?+?− pairs are identified via selections on pair momentum asymmetry and acoplanarity. Differential cross sections for dimuon production are measured in different centrality, average muon momentum, and pair rapidity intervals as functions of acoplanarity and ?⊥, the transverse momentum kick of one muon relative to the other. Measurements are also made as a function of the rapidity separation of the muons and the angle of the muon pair relative to the second-order event plane to test whether magnetic fields generated in the quark-gluon plasma affect the measured muons. A prior observation of a centrality-dependent broadening of the acoplanarity distribution is confirmed. Furthermore, the improved precision of the measurement reveals a depletion in the number of pairs having small acoplanarity or ?⊥ values in more central collisions. The acoplanarity distributions in a given centrality interval are observed to vary with the mean ?T of the muons in the pair, but the ?⊥ distributions do not. Comparisons with recent theoretical predictions are made. The predicted trends associated with effects of magnetic fields on the dimuons are not observed.
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| 41. |
- Mullier, G.A., et al.
(author)
-
Measurement of single top-quark production in the s-channel in proton-proton collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:6
-
Journal article (peer-reviewed)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 pb, consistent with the Standard Model prediction of pb.
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| 42. |
- Mullier, G.A., et al.
(author)
-
Measurement of substructure-dependent jet suppression in Pb+Pb collisions at 5.02 TeV with the ATLAS detector
- 2023
-
In: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 107:5
-
Journal article (peer-reviewed)abstract
- The ATLAS detector at the Large Hadron Collider has been used to measure jet substructure modification and suppression in Pb+Pb collisions at a nucleon–nucleon center-of-mass energy in comparison with proton–proton (pp) collisions at . The Pb+Pb data, collected in 2018, have an integrated luminosity of 1.72nb−1, while the pp data, collected in 2017, have an integrated luminosity of 260pb−1. Jets used in this analysis are clustered using the anti-kt algorithm with a radius parameter R=0.4. The jet constituents, defined by both tracking and calorimeter information, are used to determine the angular scale rg of the first hard splitting inside the jet by reclustering them using the Cambridge–Aachen algorithm and employing the soft-drop grooming technique. The nuclear modification factor, RAA, used to characterize jet suppression in Pb+Pb collisions, is presented differentially in rg, jet transverse momentum, and in intervals of collision centrality. The RAA value is observed to depend significantly on jet rg. Jets produced with the largest measured rg are found to be twice as suppressed as those with the smallest rg in central Pb+Pb collisions. The RAA values do not exhibit a strong variation with jet pT in any of the rg intervals. The rg and pT dependence of jet RAA is qualitatively consistent with a picture of jet quenching arising from coherence and provides the most direct evidence in support of this approach
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| 43. |
- Mullier, G.A., et al.
(author)
-
Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:5
-
Journal article (peer-reviewed)abstract
- This paper presents a measurement of b-jet production in Pb+Pb and pp collisions at √sNN = 5.02 TeV with the ATLAS detector at the LHC. The measurement uses 260 pb−1 of pp collisions collected in 2017 and 1.4 nb−1 of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti-kt algorithm. The b-jets are identified from a sample of jets containing muons from the semileptonic decay of b-quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b-jets are reconstructed for radius parameters R = 0.2 and R = 0.4, and only R = 0.2 jets are used in Pb+Pb collisions. For comparison, inclusive R = 0.2 jets are also measured using 1.7 nb−1 of Pb+Pb collisions collected in 2018 and the same pp collision data as the b-jet measurement. The nuclear modification factor, RAA, is calculated for both b-jets and inclusive jets with R = 0.2 over the transverse momentum range of 80–290 GeV. The nuclear modification factor for b-jets decreases from peripheral to central collisions. The ratio of the b-jet RAA to inclusive jet RAA is also presented and suggests that the RAA for b-jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions.
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| 44. |
- Mullier, G.A., et al.
(author)
-
Measurement of the total cross section and ρ-parameter from elastic scattering in pp collisions at √s=13 TeV with the ATLAS detector
- 2023
-
In: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:5
-
Journal article (peer-reviewed)abstract
- In a special run of the LHC with β* = 2.5 km, proton–proton elastic-scattering events were recorded at √s = 13 TeV with an integrated luminosity of 340 µb−1 using the ALFA subdetector of ATLAS in 2016. The elastic cross section was measured differentially in the Mandelstam t variable in the range from −t = 2.5 · 10−4 GeV2 to −t = 0.46 GeV2 using 6.9 million elastic-scattering candidates. This paper presents measurements of the total cross section σtot, parameters of the nuclear slope, and the ρ-parameter defined as the ratio of the real part to the imaginary part of the elastic-scattering amplitude in the limit t → 0. These parameters are determined from a fit to the differential elastic cross section using the optical theorem and different parameterizations of the t-dependence. The results for σtotand ρ areσtot (pp → X) = 104.7 ± 1.1 mb, ρ = 0.098 ± 0.011.The uncertainty in σtot is dominated by the luminosity measurement, and in ρ by imperfect knowledge of the detector alignment and by modelling of the nuclear amplitude.
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| 45. |
- Mullier, G.A., et al.
(author)
-
Measurement of the tt¯ production cross-section in pp collisions at √s = 5.02 TeV with the ATLAS detector
- 2023
-
In: Journal of High Energy Physics (JHEP). - : Springer Science and Business Media Deutschland GmbH. - 1126-6708 .- 1029-8479. ; 2023:6
-
Journal article (peer-reviewed)abstract
- The inclusive top-quark pair (tt¯) production cross-section σtt¯ is measured inproton–proton collisions at a centre-of-mass energy √s = 5.02 TeV, using 257 pb−1 of datacollected in 2017 by the ATLAS experiment at the LHC. The tt¯ cross-section is measuredin both the dilepton and single-lepton final states of the tt¯ system and then combined. Thecombination of the two measurements yieldsσtt¯ = 67.5 ± 0.9 (stat.) ± 2.3 (syst.) ± 1.1 (lumi.) ± 0.2 (beam) pb,where the four uncertainties reflect the limited size of the data sample, experimental andtheoretical systematic effects, and imperfect knowledge of both the integrated luminosityand the LHC beam energy, giving a total uncertainty of 3.9%. The result is in agreementwith theoretical quantum chromodynamic calculations at next-to-next-to-leading order inthe strong coupling constant, including the resummation of next-to-next-to-leading logarithmic soft-gluon terms, and constrains the parton distribution functions of the proton atlarge Bjorken-x.
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| 46. |
- Mullier, G.A., et al.
(author)
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Measurements of Higgs boson production by gluon-gluon fusion and vector-boson fusion using H→WW*→eνμν decays in pp collisions at √s=13 TeV with the ATLAS detector
- 2023
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In: Physical Review D. - : American Physical Society. - 2470-0010 .- 2470-0029. ; 108:3
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Journal article (peer-reviewed)abstract
- Higgs boson production via gluon-gluon fusion and vector-boson fusion in proton-proton collisions is measured in the H→WW*→eνμν decay channel. The Large Hadron Collider delivered proton-proton collisions at a center-of-mass energy of 13 TeV between 2015 and 2018, which were recorded by the ATLAS detector, corresponding to an integrated luminosity of 139 fb−1. The total cross sections for Higgs boson production by gluon-gluon fusion and vector-boson fusion times the H→WW* branching ratio are measured to be 12.0±1.4 and pb, respectively, in agreement with the Standard Model predictions of 10.4±0.6 and 0.81±0.02 pb. Higgs boson production is further characterized through measurements of Simplified Template Cross Sections in a total of 11 kinematic fiducial regions.
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| 47. |
- Mullier, G.A., et al.
(author)
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Measurements of W+ W- production in decay topologies inspired by searches for electroweak supersymmetry
- 2023
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In: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:8
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Journal article (peer-reviewed)abstract
- This paper presents a measurement of fiducial and differential cross-sections for W+W− production in proton–proton collisions at √s=13 TeV with the ATLAS experiment at the Large Hadron Collider using a dataset corresponding to an integrated luminosity of 139 fb−1. Events with exactly one electron, one muon and no hadronic jets are studied. The fiducial region in which the measurements are performed is inspired by searches for the electroweak production of supersymmetric charginos decaying to two-lepton final states. The selected events have moderate values of missing transverse momentum and the ‘stransverse mass’ variable mT2, which is widely used in searches for supersymmetry at the LHC. The ranges of these variables are chosen so that the acceptance is enhanced for direct W+W− production and suppressed for production via top quarks, which is treated as a background. The fiducial cross-section and particle-level differential cross-sections for six variables are measured and compared with two theoretical SM predictions from perturbative QCD calculations.
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| 48. |
- Mullier, G.A., et al.
(author)
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Search for a new Z′ gauge boson in 4μ events with the ATLAS experiment
- 2023
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In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
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Journal article (peer-reviewed)abstract
- This paper presents a search for a new Z′ vector gauge boson with the ATLAS experiment at the Large Hadron Collider using pp collision data collected at √s = 13 TeV, corresponding to an integrated luminosity of 139 fb−1. The new gauge boson Z′ is predicted by Lμ − Lτ models to address observed phenomena that can not be explained by the Standard Model. The search examines the four-muon (4μ) final state, using a deep learning neural network classifier to separate the Z′ signal from the Standard Model background events. The di-muon invariant masses in the 4μ events are used to extract the Z′ resonance signature. No significant excess of events is observed over the predicted background. Upper limits at a 95% confidence level on the Z′ production cross-section times the decay branching fraction of pp → Z′μμ → 4μ are set from 0.31 to 4.3 fb for the Z′ mass ranging from 5 to 81 GeV. The corresponding common coupling strengths, gZ′, of the Z′ boson to the second and third generation leptons above 0.003 – 0.2 have been excluded.
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| 49. |
- Mullier, G.A., et al.
(author)
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Search for boosted diphoton resonances in the 10 to 70 GeV mass range using 138 fb-1 of 13TeV pp collisions with the ATLAS detector
- 2023
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In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
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Journal article (peer-reviewed)abstract
- A search for diphoton resonances in the mass range between 10 and 70 GeV with the ATLAS experiment at the Large Hadron Collider (LHC) is presented. The analysis is based on pp collision data corresponding to an integrated luminosity of 138 fb−1 at a centre-of-mass energy of 13 TeV recorded from 2015 to 2018. Previous searches for diphoton resonances at the LHC have explored masses down to 65 GeV, finding no evidence of new particles. This search exploits the particular kinematics of events with pairs of closely spaced photons reconstructed in the detector, allowing examination of invariant masses down to 10 GeV. The presented strategy covers a region previously unexplored at hadron colliders because of the experimental challenges of recording low-energy photons and estimating the backgrounds. No significant excess is observed and the reported limits provide the strongest bound on promptly decaying axion-like particles coupling to gluons and photons for masses between 10 and 70 GeV.
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| 50. |
- Mullier, G.A., et al.
(author)
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Search for dark matter produced in association with a dark Higgs boson decaying into W+W- in the one-lepton final state at √s=13 TeV using 139 fb-1 of pp collisions recorded with the ATLAS detector
- 2023
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In: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Journal article (peer-reviewed)abstract
- Several extensions of the Standard Model predict the production of dark matter particles at the LHC. A search for dark matter particles produced in association with a dark Higgs boson decaying into W+W− in the , final states with ℓ = e, μ is presented. This analysis uses 139 fb−1 of pp collisions recorded by the ATLAS detector at a centre-of-mass energy of 13 TeV. The W± → decays are reconstructed from pairs of calorimeter-measured jets or from track-assisted reclustered jets, a technique aimed at resolving the dense topology from a pair of boosted quarks using jets in the calorimeter and tracking information. The observed data are found to agree with Standard Model predictions. Scenarios with dark Higgs boson masses ranging between 140 and 390 GeV are excluded.
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