| 1. |
- Banerjee, Avik, et al.
(författare)
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Vector-like quarks: status and new directions at the LHC
- 2024
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Tidskriftsartikel (refereegranskat)abstract
- Experimental searches for vector-like quarks have until now only considered their decays into Standard Model particles. However, various new physics scenarios predict additional scalars, so that these vector-like quarks can decay to new channels. These new channels reduce the branching ratios into Standard Model final states, significantly affecting current mass bounds. In this article, we quantitatively assess the relevance and observability of single and pair production processes of vector-like quarks, followed by decays into both standard and exotic final states. We highlight the importance of large widths and the relative interaction strengths with Standard Model particles and new scalars. Then, we review the post-Moriond 2024 status of these models in light of available LHC data and discuss potential future strategies to enhance the scope of vector-like quark searches.
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| 2. |
- Benbrik, R., et al.
(författare)
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Signatures of vector-like top partners decaying into new neutral scalar or pseudoscalar bosons
- 2020
-
Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2020:5
-
Tidskriftsartikel (refereegranskat)abstract
- We explore the phenomenology of models containing one Vector-Like Quark (VLQ), t′, which can decay into the Standard Model (SM) top quark, t, and a new spin-0 neutral boson, S, the latter being either a scalar or pseudoscalar state. We parametrise the underlying interactions in terms of a simplified model which enables us to capture possible Beyond the SM (BSM) scenarios. We discuss in particular three such scenarios: one where the SM state is supplemented by an additional scalar, one which builds upon a 2-Higgs Doublet Model (2HDM) framework and another which realises a Composite Higgs Model (CHM) through partial compositeness. Such exotic decays of the t′ can be competitive with decays into SM particles, leading to new possible discovery channels at the Large Hadron Collider (LHC). Assuming t′ pair production via strong interactions, we design signal regions optimised for one t′ → S t transition (while being inclusive on the other t¯ ′ decay, and vice versa), followed by the decay of S into the two very clean experimental signatures S → γ γ and S → Z (→ ℓ+ℓ−)γ. We perform a dedicated signal- to-background analysis in both channels, by using Monte Carlo (MC) event simulations modelling the dynamics from the proton-proton to the detector level. Under the assumption of BR(t′ → S t) = 100%, we are therefore able to realistically quantify the sensitivity of the LHC to both the t′ and S masses, assuming both current and foreseen luminosities. This approach paves the way for the LHC experiments to surpass current VLQ search strategies based solely on t′ decays into SM bosons (W±, Z , h). © 2020, The Author(s).
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| 3. |
- Aaboud, M, et al.
(författare)
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Measurement of fiducial and differential W+W- production cross-sections at √s=13 TeV with the ATLAS detector
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:10
-
Tidskriftsartikel (refereegranskat)abstract
- 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 data corresponding to an integrated luminosity of 36.1 fb - 1 is presented. Events with one electron and one muon are selected, corresponding to the decay of the diboson system as WW→ e±νμ∓ν. To suppress top-quark background, events containing jets with a transverse momentum exceeding 35 GeV are not included in the measurement phase space. The fiducial cross-section, six differential distributions and the cross-section as a function of the jet-veto transverse momentum threshold are measured and compared with several theoretical predictions. Constraints on anomalous electroweak gauge boson self-interactions are also presented in the framework of a dimension-six effective field theory. © 2019, CERN for the benefit of the ATLAS collaboration.
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| 4. |
- Aaboud, M, et al.
(författare)
-
Measurement of the azimuthal anisotropy of charged particles produced in √sNN = 5.02 TeV Pb+Pb collisions with the ATLAS detector
- 2018
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 78:12
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of the azimuthal anisotropy in lead–lead collisions at sNN = 5.02 TeV are presented using a data sample corresponding to 0.49 nb - 1 integrated luminosity collected by the ATLAS experiment at the LHC in 2015. The recorded minimum-bias sample is enhanced by triggers for “ultra-central” collisions, providing an opportunity to perform detailed study of flow harmonics in the regime where the initial state is dominated by fluctuations. The anisotropy of the charged-particle azimuthal angle distributions is characterized by the Fourier coefficients, v2–v7, which are measured using the two-particle correlation, scalar-product and event-plane methods. The goal of the paper is to provide measurements of the differential as well as integrated flow harmonics vn over wide ranges of the transverse momentum, 0.5 < pT< 60 GeV, the pseudorapidity, | η| < 2.5, and the collision centrality 0–80%. Results from different methods are compared and discussed in the context of previous and recent measurements in Pb+Pb collisions at sNN = 2.76 TeV and 5.02 TeV. In particular, the shape of the pTdependence of elliptic or triangular flow harmonics is observed to be very similar at different centralities after scaling the vn and pTvalues by constant factors over the centrality interval 0–60% and the pTrange 0.5 < pT< 5 GeV. © 2018, CERN for the benefit of the ATLAS collaboration.
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| 5. |
- Aaboud, M., et al.
(författare)
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Measurements of b-jet tagging efficiency with the ATLAS detector using tt¯" role="presentation">tt¯ events at s=13" role="presentation">s√=13 TeV
- 2018
-
Ingår i: Journal of High Energy Physics (JHEP). - : SPRINGER. - 1126-6708 .- 1029-8479. ; :8
-
Tidskriftsartikel (refereegranskat)abstract
- The efficiency to identify jets containing b-hadrons (b-jets) is measured using a high purity sample of dileptonic top quark-antiquark pairs (t (t) over bar) selected from the 36.1 fb(-1) of data collected by the ATLAS detector in 2015 and 2016 from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy root s = 13 TeV. Two methods are used to extract the efficiency from t (t) over bar events, a combinatorial likelihood approach and a tag-and-probe method. A boosted decision tree, not using b-tagging information, is used to select events in which two b-jets are present, which reduces the dominant uncertainty in the modelling of the flavour of the jets. The efficiency is extracted for jets in a transverse momentum range from 20 to 300 GeV, with data-to-simulation scale factors calculated by comparing the efficiency measured using collision data to that predicted by the simulation. The two methods give compatible results, and achieve a similar level of precision, measuring data-to-simulation scale factors close to unity with uncertainties ranging from 2% to 12% depending on the jet transverse momentum.
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| 6. |
- Aaboud, M, et al.
(författare)
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Search for a Structure in the Bs0 π± Invariant Mass Spectrum with the ATLAS Experiment
- 2018
-
Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 1079-7114 .- 0031-9007. ; 120:20
-
Tidskriftsartikel (refereegranskat)abstract
- A search for the narrow structure, X(5568), reported by the D0 Collaboration in the decay sequence X→Bs0π±, Bs0→J/ψφ, is presented. The analysis is based on a data sample recorded with the ATLAS detector at the LHC corresponding to 4.9 fb-1 of pp collisions at 7 TeV and 19.5 fb-1 at 8 TeV. No significant signal was found. Upper limits on the number of signal events, with properties corresponding to those reported by D0, and on the X production rate relative to Bs0 mesons, ρX, were determined at 95% confidence level. The results are N(X)
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| 7. |
- Aaboud, M, et al.
(författare)
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Search for exclusive Higgs and Z boson decays to ϕγ and ργ with the ATLAS detector
- 2018
-
Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2018:7
-
Tidskriftsartikel (refereegranskat)abstract
- A search for the exclusive decays of the Higgs and Z bosons to a ϕ or ρ meson and a photon is performed with a pp collision data sample corresponding to an integrated luminosity of up to 35.6 fb−1 collected at s=13 TeV with the ATLAS detector at the CERN Large Hadron Collider. These decays have been suggested as a probe of the Higgs boson couplings to light quarks. No significant excess of events is observed above the background, as expected from the Standard Model. Upper limits at 95% confidence level were obtained on the branching fractions of the Higgs boson decays to ϕγ and ργ of 4.8 × 10−4 and 8.8 × 10−4, respectively. The corresponding 95% confidence level upper limits for the Z boson decays are 0.9 × 10−6 and 25 × 10−6 for ϕγ and ργ, respectively.[Figure not available: see fulltext.]. © 2018, The Author(s).
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| 8. |
- Aaboud, M, et al.
(författare)
-
Search for Higgs boson pair production in the bb¯ WW * decay mode at √s = 13 TeV with the ATLAS detector
- 2019
-
Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2019:4
-
Tidskriftsartikel (refereegranskat)abstract
- A search for Higgs boson pair production in the bb¯ WW * decay mode is performed in the bb¯ ℓνqq final state using 36.1 fb −1 of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. No evidence of events beyond the background expectation is found. Upper limits on the non-resonant pp → HH production cross section of 10 pb and on the resonant production cross section as a function of the HH invariant mass are obtained. Resonant production limits are set for scalar and spin-2 graviton hypotheses in the mass range 500 to 3000 GeV.[Figure not available: see fulltext.] © 2019, The Author(s).
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| 9. |
- Aad, G., et al.
(författare)
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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
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Tidskriftsartikel (refereegranskat)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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| 10. |
- Aad, G, et al.
(författare)
-
Alignment of the ATLAS Inner Detector in Run 2
- 2020
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:12
-
Tidskriftsartikel (refereegranskat)abstract
- The performance of the ATLAS Inner Detector alignment has been studied using pp collision data at s=13TeV collected by the ATLAS experiment during Run 2 (2015–2018) of the Large Hadron Collider (LHC). The goal of the detector alignment is to determine the detector geometry as accurately as possible and correct for time-dependent movements. The Inner Detector alignment is based on the minimization of track-hit residuals in a sequence of hierarchical levels, from global mechanical assembly structures to local sensors. Subsequent levels have increasing numbers of degrees of freedom; in total there are almost 750,000. The alignment determines detector geometry on both short and long timescales, where short timescales describe movements within an LHC fill. The performance and possible track parameter biases originating from systematic detector deformations are evaluated. Momentum biases are studied using resonances decaying to muons or to electrons. The residual sagitta bias and momentum scale bias after alignment are reduced to less than ∼0.1TeV-1 and 0.9 × 10 - 3, respectively. Impact parameter biases are also evaluated using tracks within jets. © 2020, The Author(s).
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| 11. |
- Aad, G., et al.
(författare)
-
Anomaly detection search for new resonances decaying into a Higgs boson and a generic new particle X in hadronic final states using √s=13 TeV pp collisions with the ATLAS detector
- 2023
-
Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 108:5
-
Tidskriftsartikel (refereegranskat)abstract
- A search is presented for a heavy resonance Y decaying into a Standard Model Higgs boson H and a new particle X in a fully hadronic final state. The full Large Hadron Collider run 2 dataset of proton-proton collisions at √s=13 TeV collected by the ATLAS detector from 2015 to 2018 is used and corresponds to an integrated luminosity of 139 fb−1. The search targets the high Y-mass region, where the H and X have a significant Lorentz boost in the laboratory frame. A novel application of anomaly detection is used to define a general signal region, where events are selected solely because of their incompatibility with a learned background-only model. It is constructed using a jet-level tagger for signal-model-independent selection of the boosted X particle, representing the first application of fully unsupervised machine learning to an ATLAS analysis. Two additional signal regions are implemented to target a benchmark X decay into two quarks, covering topologies where the X is reconstructed as either a single large-radius jet or two small-radius jets. The analysis selects Higgs boson decays into , and a dedicated neural-network-based tagger provides sensitivity to the boosted heavy-flavor topology. No significant excess of data over the expected background is observed, and the results are presented as upper limits on the production cross section for signals with mY between 1.5 and 6 TeV and mX between 65 and 3000 GeV.
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| 12. |
- Aad, G, et al.
(författare)
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ATLAS data quality operations and performance for 2015-2018 data-taking
- 2020
-
Ingår i: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221. ; 15:4
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Tidskriftsartikel (refereegranskat)abstract
- The ATLAS detector at the Large Hadron Collider reads out particle collision data from over 100 million electronic channels at a rate of approximately 100 kHz, with a recording rate for physics events of approximately 1 kHz. Before being certified for physics analysis at computer centres worldwide, the data must be scrutinised to ensure they are clean from any hardware or software related issues that may compromise their integrity. Prompt identification of these issues permits fast action to investigate, correct and potentially prevent future such problems that could render the data unusable. This is achieved through the monitoring of detector-level quantities and reconstructed collision event characteristics at key stages of the data processing chain. This paper presents the monitoring and assessment procedures in place at ATLAS during 2015-2018 data-taking. Through the continuous improvement of operational procedures, ATLAS achieved a high data quality efficiency, with 95.6% of the recorded proton-proton collision data collected at s=13 TeV certified for physics analysis.
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| 13. |
- Aad, G., et al.
(författare)
-
ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset
- 2023
-
Ingår i: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:7
-
Tidskriftsartikel (refereegranskat)abstract
- The flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of √s=13 TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b-jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a sample of simulated Standard Model events; similarly, at a c-jet identification efficiency of 30%, a light-jet (b-jet) rejection factor of 70 (9) is obtained.
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| 14. |
- Aad, G., et al.
(författare)
-
Calibration of the light-flavour jet mistagging efficiency of the b-tagging algorithms with Z+jets events using 139 fb−1 of ATLAS proton–proton collision data at √s=13 TeV
- 2023
-
Ingår i: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:8
-
Tidskriftsartikel (refereegranskat)abstract
- The identification of b-jets, referred to as b-tagging, is an important part of many physics analyses in the ATLAS experiment at the Large Hadron Collider and an accurate calibration of its performance is essential for high-quality physics results. This publication describes the calibration of the light-flavour jet mistagging efficiency in a data sample of proton–proton collision events at √s=13 TeV corresponding to an integrated luminosity of 139 fb−1. The calibration is performed in a sample of Z bosons produced in association with jets. Due to the low mistagging efficiency for light-flavour jets, a method which uses modified versions of the b-tagging algorithms referred to as flip taggers is used in this work. A fit to the jet-flavour-sensitive secondary-vertex mass is performed to extract a scale factor from data, to correct the light-flavour jet mistagging efficiency in Monte Carlo simulations, while simultaneously correcting the b-jet efficiency. With this procedure, uncertainties coming from the modeling of jets from heavy-flavour hadrons are considerably lower than in previous calibrations of the mistagging scale factors, where they were dominant. The scale factors obtained in this calibration are consistent with unity within uncertainties.
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| 15. |
- Aad, G., et al.
(författare)
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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
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Tidskriftsartikel (refereegranskat)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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| 16. |
- Aad, G, et al.
(författare)
-
Combination of searches for Higgs boson pairs in pp collisions at s=13TeV with the ATLAS detector
- 2020
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 800
-
Tidskriftsartikel (refereegranskat)abstract
- This letter presents a combination of searches for Higgs boson pair production using up to 36.1 fb−1 of proton–proton collision data at a centre-of-mass energy s=13 TeV recorded with the ATLAS detector at the LHC. The combination is performed using six analyses searching for Higgs boson pairs decaying into the bb¯bb¯, bb¯W+W−, bb¯τ+τ−, W+W−W+W−, bb¯γγ and W+W−γγ final states. Results are presented for non-resonant and resonant Higgs boson pair production modes. No statistically significant excess in data above the Standard Model predictions is found. The combined observed (expected) limit at 95% confidence level on the non-resonant Higgs boson pair production cross-section is 6.9 (10) times the predicted Standard Model cross-section. Limits are also set on the ratio (κλ) of the Higgs boson self-coupling to its Standard Model value. This ratio is constrained at 95% confidence level in observation (expectation) to −5.0
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| 17. |
- Aad, G., et al.
(författare)
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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
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 842
-
Tidskriftsartikel (refereegranskat)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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| 18. |
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| 19. |
- Aad, G., et al.
(författare)
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Combined Measurement of the Higgs Boson Mass from the H → γγ and H → ZZ* → 4ℓ Decay Channels with the ATLAS Detector Using √s=7, 8, and 13 TeV pp Collision Data
- 2023
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 131:25
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Tidskriftsartikel (refereegranskat)abstract
- A measurement of the mass of the Higgs boson combining the H→ZZ*→4ℓ and H→γγ decay channels is presented. The result is based on 140 fb−1 of proton-proton collision data collected by the ATLAS detector during LHC run 2 at a center-of-mass energy of 13 TeV combined with the run 1 ATLAS mass measurement, performed at center-of-mass energies of 7 and 8 TeV, yielding a Higgs boson mass of 125.11±0.09(stat)±0.06(syst)=125.11±0.11 GeV. This corresponds to a 0.09% precision achieved on this fundamental parameter of the Standard Model of particle physics.
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| 20. |
- Aad, G., et al.
(författare)
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Combined Measurement of the Higgs Boson Mass from the H→γγ and H→ZZ∗→4ℓ Decay Channels with the ATLAS Detector Using √s=7, 8, and 13 TeV pp Collision Data
- 2023
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 131:25
-
Tidskriftsartikel (refereegranskat)abstract
- A measurement of the mass of the Higgs boson combining the H→ZZ∗→4ℓ and H→γγ decay channels is presented. The result is based on 140 fb−1 of proton-proton collision data collected by the ATLAS detector during LHC run 2 at a center-of-mass energy of 13 TeV combined with the run 1 ATLAS mass measurement, performed at center-of-mass energies of 7 and 8 TeV, yielding a Higgs boson mass of 125.11±0.09(stat)±0.06(syst)=125.11±0.11 GeV. This corresponds to a 0.09% precision achieved on this fundamental parameter of the Standard Model of particle physics.
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| 21. |
- Aad, G, et al.
(författare)
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Combined measurements of Higgs boson production and decay using up to 80 fb-1 of proton-proton collision data at s =13 TeV collected with the ATLAS experiment
- 2020
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Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 1550-2368. ; 101:1
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Tidskriftsartikel (refereegranskat)abstract
- Combined measurements of Higgs boson production cross sections and branching fractions are presented. The combination is based on the analyses of the Higgs boson decay modes H→γγ, ZZ∗, WW∗, ττ, bb, μμ, searches for decays into invisible final states, and on measurements of off-shell Higgs boson production. Up to 79.8 fb-1 of proton-proton collision data collected at s=13 TeV with the ATLAS detector are used. Results are presented for the gluon-gluon fusion and vector-boson fusion processes, and for associated production with vector bosons or top-quarks. The global signal strength is determined to be μ=1.11-0.08+0.09. The combined measurement yields an observed (expected) significance for the vector-boson fusion production process of 6.5σ (5.3σ). Measurements in kinematic regions defined within the simplified template cross section framework are also shown. The results are interpreted in terms of modifiers applied to the Standard Model couplings of the Higgs boson to other particles, and are used to set exclusion limits on parameters in two-Higgs-doublet models and in the simplified minimal supersymmetric Standard Model. No significant deviations from Standard Model predictions are observed. © 2020 CERN. © 2020 CERN, for the ATLAS Collaboration. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/" Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.
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| 22. |
- Aad, G., et al.
(författare)
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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
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Ingår i: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 843
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Tidskriftsartikel (refereegranskat)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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| 23. |
- Aad, G., et al.
(författare)
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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
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Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 107:5
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Tidskriftsartikel (refereegranskat)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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| 24. |
- Aad, G., et al.
(författare)
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Determination of the strong coupling constant from transverse energy-energy correlations in multijet events at √ s=13 TeV with the ATLAS detector
- 2023
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of transverse energy-energy correlations and their associated azimuthal asymmetries in multijet events are presented. The analysis is performed using a data sample corresponding to 139 fb-1 of proton-proton collisions at a centre-of-mass energy of root s = 13TeV, collected with the ATLAS detector at the Large Hadron Collider. The measurements are presented in bins of the scalar sum of the transverse momenta of the two leading jets and unfolded to particle level. They are then compared to next-to-next-to-leading-order perturbative QCD calculations for the first time, which feature a significant reduction in the theoretical uncertainties estimated using variations of the renormalisation and factorisation scales. The agreement between data and theory is good, thus providing a precision test of QCD at large momentum transfers Q. The strong coupling constant alpha(s) is extracted as a function of Q, showing a good agreement with the renormalisation group equation and with previous analyses. A simultaneous fit to all transverse energy-energy correlation distributions across different kinematic regions yields a value of alpha(s)( mZ) = 0.1175 +/- 0.0006 (exp.)(+0.0034) (-0.0017) (theo.), while the global fit to the asymmetry distributions yields alpha(s)(m(Z)) = 0.1185 +/- 0.0009 (exp.)(+0.0025)(-0.0012)(theo.).
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| 25. |
- Aad, G, et al.
(författare)
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Differential cross-section measurements for the electroweak production of dijets in association with a Z boson in proton–proton collisions at ATLAS
- 2021
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:2
-
Tidskriftsartikel (refereegranskat)abstract
- Differential cross-section measurements are presented for the electroweak production of two jets in association with a Z boson. These measurements are sensitive to the vector-boson fusion production mechanism and provide a fundamental test of the gauge structure of the Standard Model. The analysis is performed using proton–proton collision data collected by ATLAS at s=13TeV and with an integrated luminosity of 139fb-1. The differential cross-sections are measured in the Z→ ℓ+ℓ- decay channel (ℓ= e, μ) as a function of four observables: the dijet invariant mass, the rapidity interval spanned by the two jets, the signed azimuthal angle between the two jets, and the transverse momentum of the dilepton pair. The data are corrected for the effects of detector inefficiency and resolution and are sufficiently precise to distinguish between different state-of-the-art theoretical predictions calculated using Powheg+Pythia8, Herwig7+Vbfnlo and Sherpa 2.2. The differential cross-sections are used to search for anomalous weak-boson self-interactions using a dimension-six effective field theory. The measurement of the signed azimuthal angle between the two jets is found to be particularly sensitive to the interference between the Standard Model and dimension-six scattering amplitudes and provides a direct test of charge-conjugation and parity invariance in the weak-boson self-interactions. © 2020, The Author(s).
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| 26. |
- Aad, G, et al.
(författare)
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Dijet Resonance Search with Weak Supervision Using s =13 TeV pp Collisions in the ATLAS Detector
- 2020
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Ingår i: Physical Review Letters. - : American Physical Society (APS). - 1079-7114 .- 0031-9007. ; 125:13
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Tidskriftsartikel (refereegranskat)abstract
- This Letter describes a search for narrowly resonant new physics using a machine-learning anomaly detection procedure that does not rely on signal simulations for developing the analysis selection. Weakly supervised learning is used to train classifiers directly on data to enhance potential signals. The targeted topology is dijet events and the features used for machine learning are the masses of the two jets. The resulting analysis is essentially a three-dimensional search A→BC, for mA∼O(TeV), mB,mC∼O(100 GeV) and B, C are reconstructed as large-radius jets, without paying a penalty associated with a large trials factor in the scan of the masses of the two jets. The full run 2 s=13 TeV pp collision dataset of 139 fb-1 recorded by the ATLAS detector at the Large Hadron Collider is used for the search. There is no significant evidence of a localized excess in the dijet invariant mass spectrum between 1.8 and 8.2 TeV. Cross-section limits for narrow-width A, B, and C particles vary with mA, mB, and mC. For example, when mA=3 TeV and mBâ200 GeV, a production cross section between 1 and 5 fb is excluded at 95% confidence level, depending on mC. For certain masses, these limits are up to 10 times more sensitive than those obtained by the inclusive dijet search. These results are complementary to the dedicated searches for the case that B and C are standard model bosons. © 2020 CERN.
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| 27. |
- Aad, G., et al.
(författare)
-
Evidence for the charge asymmetry in pp ->†’ t(t)over-bar production at root ˆšs=13 TeV with the ATLAS detector
- 2023
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479.
-
Tidskriftsartikel (refereegranskat)abstract
- Inclusive and differential measurements of the top-antitop ( t (t) over bar) charge asymmetry A(C)(t (t) over bar) and the leptonic asymmetry A(C)(l (l) over bar) are presented in proton-proton collisions at root s = 13 TeV recorded by the ATLAS experiment at the CERN Large Hadron Collider. The measurement uses the complete Run 2 dataset, corresponding to an integrated luminosity of 139 fb(-1), combines data in the single-lepton and dilepton channels, and employs reconstruction techniques adapted to both the resolved and boosted topologies. A Bayesian unfolding procedure is performed to correct for detector resolution and acceptance effects. The combined inclusive t (t) over bar charge asymmetry is measured to be A(C)(t (t) over bar) = 0.0068 +/- 0.0015, which differs from zero by 4.7 standard deviations. Differential measurements are performed as a function of the invariant mass, transverse momentum and longitudinal boost of the t (t) over bar system. Both the inclusive and differential measurements are found to be compatible with the Standard Model predictions, at next-to-next-to-leading order in quantum chromodynamics perturbation theory with next-to-leading-order electroweak corrections. The measurements are interpreted in the framework of the Standard Model effective field theory, placing competitive bounds on several Wilson coefficients.
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| 28. |
- Aad, G., et al.
(författare)
-
Evidence for the Higgs Boson Decay to a Z Boson and a Photon at the LHC
- 2024
-
Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 132:2
-
Tidskriftsartikel (refereegranskat)abstract
- The first evidence for the Higgs boson decay to a Z boson and a photon is presented, with a statistical significance of 3.4 standard deviations. The result is derived from a combined analysis of the searches performed by the ATLAS and CMS Collaborations with proton-proton collision datasets collected at the CERN Large Hadron Collider (LHC) from 2015 to 2018. These correspond to integrated luminosities of around 140 fb−1 for each experiment, at a center-of-mass energy of 13 TeV. The measured signal yield is 2.2±0.7 times the standard model prediction, and agrees with the theoretical expectation within 1.9 standard deviations.
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| 29. |
- Aad, G, et al.
(författare)
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Evidence for the production of three massive vector bosons with the ATLAS detector
- 2019
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 798
-
Tidskriftsartikel (refereegranskat)abstract
- A search for the production of three massive vector bosons in proton–proton collisions is performed using data at s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider in the years 2015–2017, corresponding to an integrated luminosity of 79.8 fb−1. Events with two same-sign leptons ℓ (electrons or muons) and at least two reconstructed jets are selected to search for WWW→ℓνℓνqq. Events with three leptons without any same-flavour opposite-sign lepton pairs are used to search for WWW→ℓνℓνℓν, while events with three leptons and at least one same-flavour opposite-sign lepton pair and one or more reconstructed jets are used to search for WWZ→ℓνqqℓℓ. Finally, events with four leptons are analysed to search for WWZ→ℓνℓνℓℓ and WZZ→qqℓℓℓℓ. Evidence for the joint production of three massive vector bosons is observed with a significance of 4.1 standard deviations, where the expectation is 3.1 standard deviations. © 2019 The Author(s)
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| 30. |
- Aad, G, et al.
(författare)
-
Evidence for tt¯ tt¯ production in the multilepton final state in proton–proton collisions at √s=13 TeV with the ATLAS detector
- 2020
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:11
-
Tidskriftsartikel (refereegranskat)abstract
- A search is presented for four-top-quark production using an integrated luminosity of 139 fb- 1 of proton–proton collision data at a centre-of-mass energy of 13TeV collected by the ATLAS detector at the LHC. Events are selected if they contain a same-sign lepton pair or at least three leptons (electrons or muons). Jet multiplicity, jet flavour and event kinematics are used to separate signal from the background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The four-top-quark production cross section is measured to be 24-6+7 fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 4.3 (2.4) standard deviations and provides evidence for this process. © 2020, CERN for the benefit of the ATLAS collaboration.
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| 31. |
- Aad, G., et al.
(författare)
-
Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in ZZ → 4ℓ events with the ATLAS detector at √ˆšs=13 TeV
- 2023
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :12
-
Tidskriftsartikel (refereegranskat)abstract
- A study of the polarisation and CP properties in ZZ production is presented. The used data set corresponds to an integrated luminosity of 140 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13TeV recorded by the ATLAS detector at the Large Hadron Collider. The ZZ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised Z bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be 2.45 +/- 0.60 fb, consistent with the next-to-leadingorder Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.
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| 32. |
- Aad, G., et al.
(författare)
-
Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in ZZ → 4ℓ events with the ATLAS detector at √s=13 TeV
- 2023
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2023:12
-
Tidskriftsartikel (refereegranskat)abstract
- A study of the polarisation and CP properties in ZZ production is presented. The used data set corresponds to an integrated luminosity of 140 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. The ZZ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised Z bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be 2.45 ± 0.60 fb, consistent with the next-to-leading-order Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.
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| 33. |
- Aad, G, et al.
(författare)
-
Exclusive dimuon production in ultraperipheral Pb + Pb collisions at √sNN= 5.02 TeV with ATLAS
- 2021
-
Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 104:2
-
Tidskriftsartikel (refereegranskat)abstract
- Exclusive dimuon production in ultraperipheral collisions (UPC), resulting from photon-photon interactions in the strong electromagnetic fields of colliding high-energy lead nuclei, PbPb(γγ) → μ+μ-(Pb(∗)Pb(∗)), is studied using Lint = 0.48 nb-1 of √sNN = 5.02 TeV lead-lead collision data at the LHC with the ATLAS detector. Dimuon pairs are measured in the fiducial region pT,μ > 4 GeV, |ημ| <2.4, invariant mass mμμ > 10 GeV, and pT,μμ <2 GeV. The primary background from single-dissociative processes is extracted from the data using a template fitting technique. Differential cross sections are presented as a function of mμμ, absolute pair rapidity (|yμμ|), scattering angle in the dimuon rest frame (|cos $μμ∗|), and the colliding photon energies. The total cross section of the UPC γγ → μ+μ- process in the fiducial volume is measured to be σfidμμ = 34.1±0.3(stat.)±0.7(syst.) μb. Generally good agreement is found with calculations from STARlight, which incorporate the leading-order Breit-Wheeler process with no final-state effects, albeit differences between the measurements and theoretical expectations are observed. In particular, the measured cross sections at larger |yμμ| are found to be about 10-20% larger in data than in the calculations, suggesting the presence of larger fluxes of photons in the initial state. Modification of the dimuon cross sections in the presence of forward and/or backward neutron production is also studied and is found to be associated with a harder incoming photon spectrum, consistent with expectations. © 2021 CERN.
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| 34. |
- Aad, G., et al.
(författare)
-
Fast b-tagging at the high-level trigger of the ATLAS experiment in LHC Run 3
- 2023
-
Ingår i: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221. ; 18:11
-
Tidskriftsartikel (refereegranskat)abstract
- The ATLAS experiment relies on real-time hadronic jet reconstruction and b-tagging to record fully hadronic events containing b-jets. These algorithms require track reconstruction, which is computationally expensive and could overwhelm the high-level-trigger farm, even at the reduced event rate that passes the ATLAS first stage hardware-based trigger. In LHC Run 3, ATLAS has mitigated these computational demands by introducing a fast neural-network-based b-tagger, which acts as a low-precision filter using input from hadronic jets and tracks. It runs after a hardware trigger and before the remaining high-level-trigger reconstruction. This design relies on the negligible cost of neural-network inference as compared to track reconstruction, and the cost reduction from limiting tracking to specific regions of the detector. In the case of Standard Model HH -> b (b) over barb (b) over bar, a key signature relying on b-jet triggers, the filter lowers the input rate to the remaining high-level trigger by a factor of five at the small cost of reducing the overall signal efficiency by roughly 2%.
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| 35. |
- Aad, G., et al.
(författare)
-
Fast b-tagging at the high-level trigger of the ATLAS experiment in LHC Run 3
- 2023
-
Ingår i: Journal of Instrumentation. - : Institute of Physics. - 1748-0221. ; 18:11
-
Tidskriftsartikel (refereegranskat)abstract
- The ATLAS experiment relies on real-time hadronic jet reconstruction and b-tagging to record fully hadronic events containing b-jets. These algorithms require track reconstruction, which is computationally expensive and could overwhelm the high-level-trigger farm, even at the reduced event rate that passes the ATLAS first stage hardware-based trigger. In LHC Run 3, ATLAS has mitigated these computational demands by introducing a fast neural-network-based b-tagger, which acts as a low-precision filter using input from hadronic jets and tracks. It runs after a hardware trigger and before the remaining high-level-trigger reconstruction. This design relies on the negligible cost of neural-network inference as compared to track reconstruction, and the cost reduction from limiting tracking to specific regions of the detector. In the case of Standard Model HH → bb̅bb̅, a key signature relying on b-jet triggers, the filter lowers the input rate to the remaining high-level trigger by a factor of five at the small cost of reducing the overall signal efficiency by roughly 2%.
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| 36. |
- Aad, G., et al.
(författare)
-
Higgs boson production cross-section measurements and their EFT interpretation in the 4ℓ decay channel at s√=13 TeV with the ATLAS detector
- 2020
-
Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6052 .- 1434-6044. ; 80:10
-
Tidskriftsartikel (refereegranskat)abstract
- Higgs boson properties are studied in the four-lepton decay channel (where lepton = e, μ) using 139 fb−1 of proton–proton collision data recorded at s√=13 TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio for H→ZZ∗ decay is measured to be 1.34±0.12 pb for a Higgs boson with absolute rapidity below 2.5, in good agreement with the Standard Model prediction of 1.33±0.08 pb. Cross-sections times branching ratio are measured for the main Higgs boson production modes in several exclusive phase-space regions. The measurements are interpreted in terms of coupling modifiers and of the tensor structure of Higgs boson interactions using an effective field theory approach. Exclusion limits are set on the CP-even and CP-odd ‘beyond the Standard Model’ couplings of the Higgs boson to vector bosons, gluons and top quarks.
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| 37. |
- Aad, G, et al.
(författare)
-
Identification of boosted Higgs bosons decaying into b-quark pairs with the ATLAS detector at 13 TeV
- 2019
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:10
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes a study of techniques for identifying Higgs bosons at high transverse momenta decaying into bottom-quark pairs, H→ bb¯ , for proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy s=13 TeV. These decays are reconstructed from calorimeter jets found with the anti-ktR= 1.0 jet algorithm. To tag Higgs bosons, a combination of requirements is used: b-tagging of R= 0.2 track-jets matched to the large-R calorimeter jet, and requirements on the jet mass and other jet substructure variables. The Higgs boson tagging efficiency and corresponding multijet and hadronic top-quark background rejections are evaluated using Monte Carlo simulation. Several benchmark tagging selections are defined for different signal efficiency targets. The modelling of the relevant input distributions used to tag Higgs bosons is studied in 36 fb- 1 of data collected in 2015 and 2016 using g→ bb¯ and Z(→ bb¯) γ event selections in data. Both processes are found to be well modelled within the statistical and systematic uncertainties. © 2019, CERN for the benefit of the ATLAS collaboration.
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| 38. |
- Aad, G., et al.
(författare)
-
Inclusive and differential cross-sections for dilepton t(t)over-bar production measured in root ˆšs=13 TeV pp collisions with the ATLAS detector
- 2023
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479.
-
Tidskriftsartikel (refereegranskat)abstract
- Differential and double-differential distributions of kinematic variables of leptons from decays of top-quark pairs (t (t) over bar) are measured using the full LHC Run 2 data sample collected with the ATLAS detector. The data were collected at a pp collision energy of root s = 13TeV and correspond to an integrated luminosity of 140 fb(-1). The measurements use events containing an oppositely charged e mu pair and b-tagged jets. The results are compared with predictions from several Monte Carlo generators. While no prediction is found to be consistent with all distributions, a better agreement with measurements of the lepton p(T) distributions is obtained by reweighting the t (t) over bar sample so as to reproduce the top-quark p(T) distribution from an NNLO calculation. The inclusive top-quark pair production cross-section is measured as well, both in a fiducial region and in the full phase-space. The total inclusive cross-section is found to be sigma(t (t) over bar) = 829 +/- 1 (stat) +/- 13 (syst) +/- 8 (lumi) +/- 2 (beam) pb, where the uncertainties are due to statistics, systematic effects, the integrated luminosity and the beam energy. This is in excellent agreement with the theoretical expectation.
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| 39. |
- Aad, G., et al.
(författare)
-
Inclusive-photon production and its dependence on photon isolation in pp collisions at √s=13 TeV using 139 fb-1 of ATLAS data
- 2023
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2023:7
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of differential cross sections are presented for inclusive isolated photon production in pp collisions at a centre-of-mass energy of 13TeV provided by the LHC and using 139 fb-1 of data recorded by the ATLAS experiment. The cross sections are measured as functions of the photon transverse energy in different regions of photon pseudorapidity. The photons are required to be isolated by means of a fixed-cone method with two different cone radii. The dependence of the inclusive-photon production on the photon isolation is investigated by measuring the fiducial cross sections as functions of the isolation-cone radius and the ratios of the differential cross sections with different radii in different regions of photon pseudorapidity. The results presented in this paper constitute an improvement with respect to those published by ATLAS earlier: the measurements are provided for different isolation radii and with a more granular segmentation in photon pseudorapidity that can be exploited in improving the determination of the proton parton distribution functions. These improvements provide a more in-depth test of the theoretical predictions. Next-to-leading-order QCD predictions from JETPHOX and SHERPA and next-to-next-to-leading-order QCD predictions from NNLOJET are compared to the measurements, using several parameterisations of the proton parton distribution functions. The measured cross sections are well described by the fixed-order QCD predictions within the experimental and theoretical uncertainties in most of the investigated phase-space region.
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| 40. |
- Aad, G., et al.
(författare)
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Integrated and differential fiducial cross-section measurements for the vector boson fusion production of the Higgs boson in the H → WW* → eνμν decay channel at 13 TeV with the ATLAS detector
- 2023
-
Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 108:7
-
Tidskriftsartikel (refereegranskat)abstract
- The vector-boson production cross section for the Higgs boson decay in the H→WW*→eνμν channel is measured as a function of kinematic observables sensitive to the Higgs boson production and decay properties as well as integrated in a fiducial phase space. The analysis is performed using the proton-proton collision data collected by the ATLAS detector in Run 2 of the LHC at √s=13 TeV center-of-mass energy, corresponding to an integrated luminosity of 139 fb−1. The different flavor final state is studied by selecting an electron and a muon originating from a pair of W bosons and compatible with the Higgs boson decay. The data are corrected for the effects of detector inefficiency and resolution, and the measurements are compared with different state-of-the-art theoretical predictions. The differential cross sections are used to constrain anomalous interactions described by dimension-six operators in an effective field theory.
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| 41. |
- Aad, G, et al.
(författare)
-
Jet energy scale and resolution measured in proton–proton collisions at √s=13 TeV with the ATLAS detector
- 2021
-
Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 81:8
-
Tidskriftsartikel (refereegranskat)abstract
- Jet energy scale and resolution measurements with their associated uncertainties are reported for jets using 36–81 fb−1 of proton–proton collision data with a centre-of-mass energy of s√=13 TeV collected by the ATLAS detector at the LHC. Jets are reconstructed using two different input types: topo-clusters formed from energy deposits in calorimeter cells, as well as an algorithmic combination of charged-particle tracks with those topo-clusters, referred to as the ATLAS particle-flow reconstruction method. The anti-kt jet algorithm with radius parameter R=0.4 is the primary jet definition used for both jet types. This result presents new jet energy scale and resolution measurements in the high pile-up conditions of late LHC Run 2 as well as a full calibration of particle-flow jets in ATLAS. Jets are initially calibrated using a sequence of simulation-based corrections. Next, several in situ techniques are employed to correct for differences between data and simulation and to measure the resolution of jets. The systematic uncertainties in the jet energy scale for central jets (|η|<1.2) vary from 1% for a wide range of high-pT jets (2502.5 TeV). The relative jet energy resolution is measured and ranges from (24±1.5)% at 20 GeV to (6±0.5)% at 300 GeV.
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| 42. |
- Aad, G., et al.
(författare)
-
Longitudinal Flow Decorrelations in Xe plus Xe Collisions at √sNN=5.44 TeV with the ATLAS Detector
- 2021
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 126:12
-
Tidskriftsartikel (refereegranskat)abstract
- The first measurement of longitudinal decorrelations of harmonic flow amplitudes v(n) for n = 2-4 in Xe + Xe collisions at root s(NN) = 5.44 TeV is obtained using 3 mu b(-1) of data with the ATLAS detector at the LHC. The decorrelation signal for v(3) and v(4) is found to be nearly independent of collision centrality and transverse momentum (p(T)) requirements on fmal-state particles, but for v(2) a strong centrality and p(T) dependence is seen. When compared with the results from Pb + Pb collisions at. root s(NN) = 5.02 TcV, the longitudinal decorrelation signal in midcentral Xe + Xe collisions is found to be larger for v(2), but smaller for v(3). Current hydrodynamic models reproduce the ratios of the v(n) measured in Xe + Xe collisions to those in Pb + Pb collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between Xe + Xe and Pb + Pb. The results on the system-size dependence provide new insights and an important lever arm to separate effects of the longitudinal structure of the initial state from other early and late time effects in heavy-ion collisions.
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| 43. |
- Aad, G., et al.
(författare)
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Luminosity determination in pp collisions at √s=13 TeV using the ATLAS detector at the LHC
- 2023
-
Ingår i: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 83:10
-
Tidskriftsartikel (refereegranskat)abstract
- The luminosity determination for the ATLAS detector at the LHC during Run 2 is presented, with pp collisions at a centre-of-mass energy s=13 TeV. The absolute luminosity scale is determined using van der Meer beam separation scans during dedicated running periods in each year, and extrapolated to the physics data-taking regime using complementary measurements from several luminosity-sensitive detectors. The total uncertainties in the integrated luminosity for each individual year of data-taking range from 0.9% to 1.1%, and are partially correlated between years. After standard data-quality selections, the full Run 2 pp data sample corresponds to an integrated luminosity of 140.1 ± 1.2 fb - 1 , i.e. an uncertainty of 0.83%. A dedicated sample of low-pileup data recorded in 2017–2018 for precision Standard Model physics measurements is analysed separately, and has an integrated luminosity of 338.1 ± 3.1 pb - 1 . © 2023, The Author(s).
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| 44. |
- Aad, G, et al.
(författare)
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Measurement of angular and momentum distributions of charged particles within and around jets in Pb+Pb and pp collisions at sNN =5.02 TeV with the ATLAS detector
- 2019
-
Ingår i: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 100:6
-
Tidskriftsartikel (refereegranskat)abstract
- Studies of the fragmentation of jets into charged particles in heavy-ion collisions can provide information about the mechanism of jet quenching by the hot and dense QCD matter created in such collisions, the quark-gluon plasma. This paper presents a measurement of the angular distribution of charged particles around the jet axis in sNN=5.02 TeV Pb+Pb and pp collisions, using the ATLAS detector at the LHC. The Pb+Pb and pp data sets have integrated luminosities of 0.49nb-1 and 25pb-1, respectively. The measurement is performed for jets reconstructed with the anti-kt algorithm with radius parameter R=0.4 and is extended to an angular distance of r=0.8 from the jet axis. Results are presented as a function of Pb+Pb collision centrality and distance from the jet axis for charged particles with transverse momenta in the 1- to 63-GeV range, matched to jets with transverse momenta in the 126- to 316-GeV range and an absolute value of jet rapidity of less than 1.7. Modifications to the measured distributions are quantified by taking a ratio to the measurements in pp collisions. Yields of charged particles with transverse momenta below 4 GeV are observed to be increasingly enhanced as a function of angular distance from the jet axis, reaching a maximum at r=0.6. Charged particles with transverse momenta above 4 GeV have an enhanced yield in Pb+Pb collisions in the jet core for angular distances up to r=0.05 from the jet axis, with a suppression at larger distances.
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| 45. |
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| 46. |
- Aad, G, et al.
(författare)
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Measurement of Azimuthal Anisotropy of Muons from Charm and Bottom Hadrons in pp Collisions at s =13 TeV with the ATLAS Detector
- 2020
-
Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 1079-7114 .- 0031-9007. ; 124:8
-
Tidskriftsartikel (refereegranskat)abstract
- The elliptic flow of muons from the decay of charm and bottom hadrons is measured in pp collisions at √s=13 TeV using a data sample with an integrated luminosity of 150 pb-1 recorded by the ATLAS detector at the LHC. The muons from heavy-flavor decay are separated from light-hadron decay muons using momentum imbalance between the tracking and muon spectrometers. The heavy-flavor decay muons are further separated into those from charm decay and those from bottom decay using the distance-of-closest-approach to the collision vertex. The measurement is performed for muons in the transverse momentum range 4-7 GeV and pseudorapidity range |η| < 2.4. A significant nonzero elliptic anisotropy coefficient v2 is observed for muons from charm decays, while the v2 value for muons from bottom decays is consistent with zero within uncertainties.
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| 47. |
- Aad, G, et al.
(författare)
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Measurement of b-quark fragmentation properties in jets using the decay B± → J/ψK± in pp collisions at s√ = 13 TeV with the ATLAS detector
- 2021
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Ingår i: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; 2021:12
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Tidskriftsartikel (refereegranskat)abstract
- The fragmentation properties of jets containing b-hadrons are studied using charged B mesons in 139 fb−1 of pp collisions at s√ = 13 TeV, recorded with the ATLAS detector at the LHC during the period from 2015 to 2018. The B mesons are reconstructed using the decay of B± into J/ψK±, with the J/ψ decaying into a pair of muons. Jets are reconstructed using the anti-kt algorithm with radius parameter R = 0.4. The measurement determines the longitudinal and transverse momentum profiles of the reconstructed B hadrons with respect to the axes of the jets to which they are geometrically associated. These distributions are measured in intervals of the jet transverse momentum, ranging from 50 GeV to above 100 GeV. The results are corrected for detector effects and compared with several Monte Carlo predictions using different parton shower and hadronisation models. The results for the longitudinal and transverse profiles provide useful inputs to improve the description of heavy-flavour fragmentation in jets.
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| 48. |
- Aad, G, et al.
(författare)
-
Measurement of differential cross sections for single diffractive dissociation in √s = 8 TeV pp collisions using the ATLAS ALFA spectrometer
- 2020
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Ingår i: Journal of High Energy Physics. - : Springer Nature. - 1029-8479 .- 1126-6708. ; 2020:2
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Tidskriftsartikel (refereegranskat)abstract
- A dedicated sample of Large Hadron Collider proton-proton collision data at centre-of-mass energy s = 8 TeV is used to study inclusive single diffractive dissociation, pp → X p. The intact final-state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system X are measured in the central detector components. The fiducial range of the measurement is −4.0 < log10ξ < −1.6 and 0.016 < |t| < 0.43 GeV2, where ξ is the proton fractional energy loss and t is the squared four-momentum transfer. The total cross section integrated across the fiducial range is 1.59 ± 0.13 mb. Cross sections are also measured differentially as functions of ξ, t, and ∆η, a variable that characterises the rapidity gap separating the proton and the system X. The data are consistent with an exponential t dependence, dσ/dt ∝ eBt with slope parameter B = 7.65 ± 0.34 GeV−2. Interpreted in the framework of triple Regge phenomenology, the ξ dependence leads to a pomeron intercept of α(0) = 1.07 ± 0.09. [Figure not available: see fulltext.] © 2020, The Author(s).
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| 49. |
- Aad, G, et al.
(författare)
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Measurement of distributions sensitive to the underlying event in inclusive Z boson production in pp collisions at √s = 13 TeV with the ATLAS detector
- 2019
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 79:8
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents measurements of charged-particle distributions sensitive to the properties of the underlying event in events containing a Z boson decaying into a muon pair. The data were obtained using the ATLAS detector at the LHC in proton–proton collisions at a centre-of-mass energy of 13 Te with an integrated luminosity of 3.2fb-1. Distributions of the charged-particle multiplicity and of the charged-particle transverse momentum are measured in regions of the azimuth defined relative to the Z boson direction. The measured distributions are compared with the predictions of various Monte Carlo generators which implement different underyling event models. The Monte Carlo model predictions qualitatively describe the data well, but with some significant discrepancies. © 2019, CERN for the benefit of the ATLAS collaboration.
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| 50. |
- Aad, G., et al.
(författare)
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Measurement of electroweak Z(v (v)over-bar)gamma jj production and limits on anomalous quartic gauge couplings in pp collisions at root s=13 TeV with the ATLAS detector
- 2023
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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
- The electroweak production of Z(v (v) over bar)gamma in association with two jets is studied in a regime with a photon of high transverse momentum above 150 GeV using proton-proton collisions at a centre-of-mass energy of 13TeV at the Large Hadron Collider. The analysis uses a data sample with an integrated luminosity of 139 fb(-1) collected by the ATLAS detector during the 2015-2018 LHC data-taking period. This process is an important probe of the electroweak symmetry breaking mechanism in the Standard Model and is sensitive to quartic gauge boson couplings via vector-boson scattering. The fiducial Z( v (v) over bar)gamma jj cross section for electroweak production is measured to be 0.77(-0.30)(+0.34) fb and is consistent with the Standard Model prediction. Evidence of electroweak Z( v (v) over bar)gamma jj production is found with an observed significance of 3.2 sigma for the background-only hypothesis, compared with an expected significance of 3.7 sigma. The combination of this result with the previously published ATLAS observation of electroweak Z(v (v) over bar)gamma jj production yields an observed (expected) signal significance of 6.3 sigma (6.6 sigma). Limits on anomalous quartic gauge boson couplings are obtained in the framework of effective field theory with dimension-8 operators.
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