| 1. |
- 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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| 2. |
- Aad, G., et al.
(författare)
-
Measurement of the Centrality Dependence of the Dijet Yield in p+Pb Collisions at √sNN=8.16 TeV with the ATLAS Detector
- 2024
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 132:10
-
Tidskriftsartikel (refereegranskat)abstract
- ATLAS measured the centrality dependence of the dijet yield using 165 nb−1 of p+Pb data collected at √sNN=8.16 TeV in 2016. The event centrality, which reflects the p+Pb impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, RCP, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The RCP shows a scaling with the Bjorken x of the parton originating from the proton, xp, while no such trend is observed as a function of xPb. This analysis provides unique input to understanding the role of small proton spatial configurations in p+Pb collisions by covering parton momentum fractions from the valence region down to xp∼10−3 and xPb∼4×10−4.
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| 3. |
- Aad, G., et al.
(författare)
-
Measurement of the H→ γγ and H→ ZZ∗→ 4 ℓ cross-sections in pp collisions at √s=13.6 TeV with the ATLAS detector
- 2024
-
Ingår i: European Physical Journal C. - : Institute for Ionics. - 1434-6044 .- 1434-6052. ; 84:1
-
Tidskriftsartikel (refereegranskat)abstract
- The inclusive Higgs boson production cross-section is measured in the di-photon and the ZZ∗→ 4 ℓ decay channels using 31.4 and 29.0 fb - 1 of pp collision data respectively, collected with the ATLAS detector at a centre-of-mass energy of s=13.6 TeV . To reduce the model dependence, the measurement in each channel is restricted to a particle-level phase space that closely matches the channel’s detector-level kinematic selection, and it is corrected for detector effects. These measured fiducial cross-sections are σfid,γγ= 76-13+14 fb, and σfid,4ℓ= 2.80±0.74 fb, in agreement with the corresponding Standard Model predictions of 67.6 ± 3.7 fb and 3.67 ± 0.19 fb. Assuming Standard Model acceptances and branching fractions for the two channels, the fiducial measurements are extrapolated to the full phase space yielding total cross-sections of σ(pp→H)=67-11+12 pb and 46 ± 12 pb at 13.6 TeV from the di-photon and ZZ∗→ 4 ℓ measurements respectively. The two measurements are combined into a total cross-section measurement of σ(pp→ H) = 58.2 ± 8.7 pb, to be compared with the Standard Model prediction of σ(pp→ H) SM= 59.9 ± 2.6 pb.
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| 4. |
- Aad, G., et al.
(författare)
-
Measurement of the production cross-section of J/ψ and ψ(2S) mesons in pp collisions at √s=13 TeV with the ATLAS detector
- 2024
-
Ingår i: European Physical Journal C. - : Springer Nature. - 1434-6044 .- 1434-6052. ; 84:2
-
Tidskriftsartikel (refereegranskat)abstract
- Measurements of the differential production cross-sections of prompt and non-prompt ?/? and ?(2S) mesons with transverse momenta between 8 and 360 GeV and rapidity in the range |?|<2 are reported. Furthermore, measurements of the non-prompt fractions of ?/? and ?(2S), and the prompt and non-prompt ?(2S)-to-?/? production ratios, are presented. The analysis is performed using 140 fb−1 of √?=13 TeV pp collision data recorded by the ATLAS detector at the LHC during the years 2015–2018.
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| 5. |
- Aad, G., et al.
(författare)
-
Measurement of the t¯t¯ cross section and its ratio to the Z production cross section using pp collisions at √s=13.6 TeV with the ATLAS detector
- 2024
-
Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 848
-
Tidskriftsartikel (refereegranskat)abstract
- The inclusive top-quark-pair production cross section ???̄ and its ratio to the ?-boson production cross section have been measured in proton–proton collisions at √? = 13.6 TeV, using 29 fb−1 of data collected in 2022 with the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge electron-muon pair and ?-tagged jets, and assuming Standard Model decays, the top-quark-pair production cross section is measured to be ???̄ = 850± 3(stat.) ± 18(syst.) ± 20(lumi.) pb. The ratio of the ??̄ and the ?-boson production cross sections is also measured, where the ?-boson contribution is determined for inclusive ?+?− and ?+?− events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the ??̄ cross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, ???̄∕? = 1.145 ± 0.003(stat.) ± 0.021(syst.)±0.002(lumi.) is consistent with the Standard Model prediction using the PDF4LHC21 PDF set.
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| 6. |
- Aad, G., et al.
(författare)
-
Observation of WZγ Production in pp Collisions at √s=13 TeV with the ATLAS Detector
- 2024
-
Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 132:2
-
Tidskriftsartikel (refereegranskat)abstract
- This Letter reports the observation of WZγ production and a measurement of its cross section using 140.1±1.2 fb−1 of proton-proton collision data recorded at a center-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. The WZγ production cross section, with both the W and Z bosons decaying leptonically, pp→WZγ→ℓ′±νℓ+ℓ−γ (ℓ(′)=e, μ), is measured in a fiducial phase-space region defined such that the leptons and the photon have high transverse momentum and the photon is isolated. The cross section is found to be 2.01±0.30(stat)±0.16(syst) fb. The corresponding standard model predicted cross section calculated at next-to-leading order in perturbative quantum chromodynamics and at leading order in the electroweak coupling constant is 1.50±0.06 fb. The observed significance of the WZγ signal is 6.3σ, compared with an expected significance of 5.0σ.
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| 7. |
- Aad, G., et al.
(författare)
-
Performance and calibration of quark/gluon-jet taggers using 140 fb-1 of pp collisions at √s=13 TeV with the ATLAS detector
- 2024
-
Ingår i: Chinese Physics C. - : Institute of Physics Publishing (IOPP). - 1674-1137 .- 2058-6132. ; 48:2
-
Tidskriftsartikel (refereegranskat)abstract
- The identification of jets originating from quarks and gluons, often referred to as quark/gluon tagging, plays an important role in various analyses performed at the Large Hadron Collider, as Standard Model measurements and searches for new particles decaying to quarks often rely on suppressing a large gluon-induced background. This paper describes the measurement of the efficiencies of quark/gluon taggers developed within the ATLAS Collaboration, using √s = 13 TeV proton-proton collision data with an integrated luminosity of 140 fb-1 collected by the ATLAS experiment. Two taggers with high performances in rejecting jets from gluon over jets from quarks are studied: one tagger is based on requirements on the number of inner-detector tracks associated with the jet, and the other combines several jet substructure observables using a boosted decision tree. A method is established to determine the quark/gluon fraction in data, by using quark/gluon-enriched subsamples defined by the jet pseudorapidity. Differences in tagging efficiency between data and simulation are provided for jets with transverse momentum between 500 GeV and 2 TeV and for multiple tagger working points.
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| 8. |
- Aad, G., et al.
(författare)
-
Performance and calibration of quark/gluon-jet taggers using 140 fb-1 of pp collisions at √s=13 TeV with the ATLAS detector
- 2024
-
Ingår i: Chinese Physics C. - : IOP Publishing. - 1674-1137 .- 2058-6132. ; 48:2
-
Tidskriftsartikel (refereegranskat)abstract
- The identification of jets originating from quarks and gluons, often referred to as quark/gluon tagging, plays an important role in various analyses performed at the Large Hadron Collider, as Standard Model measurements and searches for new particles decaying to quarks often rely on suppressing a large gluon-induced background. This paper describes the measurement of the efficiencies of quark/gluon taggers developed within the ATLAS Collaboration, using √?=13 TeV proton–proton collision data with an integrated luminosity of 140 fb−1 collected by the ATLAS experiment. Two taggers with high performances in rejecting jets from gluon over jets from quarks are studied: one tagger is based on requirements on the number of inner-detector tracks associated with the jet, and the other combines several jet substructure observables using a boosted decision tree. A method is established to determine the quark/gluon fraction in data, by using quark/gluon-enriched subsamples defined by the jet pseudorapidity. Differences in tagging efficiency between data and simulation are provided for jets with transverse momentum between 500 GeV and 2 TeV and for multiple tagger working points.
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| 9. |
- Aad, G., et al.
(författare)
-
Search for a CP-odd Higgs boson decaying into a heavy CP-even Higgs boson and a Z boson in the l+l-t(t)over-bar and Μ(Μ)over-barb(b)over-bar final states using 140 fb-1 of data collected with the ATLAS detector
- 2024
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :2
-
Tidskriftsartikel (refereegranskat)abstract
- A search for a heavy CP-odd Higgs boson, A, decaying into a Z boson and a heavy CP-even Higgs boson, H, is presented. It uses the full LHC Run 2 dataset of pp collisions at root s = 13TeV collected with the ATLAS detector, corresponding to an integrated luminosity of 140 fb(-1). The search for A -> ZH is performed in the l(+)l(-)t (t) over bar t and nu(nu) over barb (b) over bar final states and surpasses the reach of previous searches in different final states in the region with m(H) > 350 GeV and m(A) > 800 GeV. No significant deviation from the Standard Model expectation is found. Upper limits are placed on the production cross-section times the decay branching ratios. Limits with less model dependence are also presented as functions of the reconstructed m(t (t) over bar) and m(b (b) over bar) distributions in the l(+)l(-)t (t) over bar and nu(nu) over barb (b) over bar channels, respectively. In addition, the results are interpreted in the context of two-Higgs-doublet models.
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| 10. |
- Aad, G., et al.
(författare)
-
Search for resonant production of dark quarks in the dijet final state with the ATLAS detector
- 2024
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2024:2
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a search for a new Z' resonance decaying into a pair of dark quarks which hadronise into dark hadrons before promptly decaying back as Standard Model particles. This analysis is based on proton-proton collision data recorded at root s = 13TeV with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to an integrated luminosity of 139 fb(-1). After selecting events containing large-radius jets with high track multiplicity, the invariant mass distribution of the two highest-transverse-momentum jets is scanned to look for an excess above a data-driven estimate of the Standard Model multijet background. No significant excess of events is observed and the results are thus used to set 95% confidence-level upper limits on the production cross-section times branching ratio of the Z' to dark quarks as a function of the Z' mass for various dark-quark scenarios.
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| 11. |
- Aad, G., et al.
(författare)
-
Search for resonant production of dark quarks in the dijet final state with the ATLAS detector
- 2024
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2024:2
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a search for a new Z′ resonance decaying into a pair of dark quarks which hadronise into dark hadrons before promptly decaying back as Standard Model particles. This analysis is based on proton-proton collision data recorded at √? = 13 TeV with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to an integrated luminosity of 139 fb−1. After selecting events containing large-radius jets with high track multiplicity, the invariant mass distribution of the two highest-transverse-momentum jets is scanned to look for an excess above a data-driven estimate of the Standard Model multijet background. No significant excess of events is observed and the results are thus used to set 95% confidence-level upper limits on the production cross-section times branching ratio of the Z′ to dark quarks as a function of the Z′ mass for various dark-quark scenarios.
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| 12. |
- Aad, G., et al.
(författare)
-
Studies of new Higgs boson interactions through nonresonant HH production in the b¯bγγ final state in pp collisions at √s = 13 TeV with the ATLAS detector
- 2024
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2024:1
-
Tidskriftsartikel (refereegranskat)abstract
- A search for nonresonant Higgs boson pair production in the final state is performed using 140 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. This analysis supersedes and expands upon the previous nonresonant ATLAS results in this final state based on the same data sample. The analysis strategy is optimised to probe anomalous values not only of the Higgs (H) boson self-coupling modifier κλ but also of the quartic HHVV (V = W, Z) coupling modifier κ2V. No significant excess above the expected background from Standard Model processes is observed. An observed upper limit μHH < 4.0 is set at 95% confidence level on the Higgs boson pair production cross-section normalised to its Standard Model prediction. The 95% confidence intervals for the coupling modifiers are −1.4 < κλ < 6.9 and −0.5 < κ2V < 2.7, assuming all other Higgs boson couplings except the one under study are fixed to the Standard Model predictions. The results are interpreted in the Standard Model effective field theory and Higgs effective field theory frameworks in terms of constraints on the couplings of anomalous Higgs boson (self-)interactions.
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| 13. |
- Aad, G., et al.
(författare)
-
Study of Z → llγ decays at √s=8 TeV with the ATLAS detector
- 2024
-
Ingår i: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 84:2
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a study of ?→??? decays with the ATLAS detector at the Large Hadron Collider. The analysis uses a proton–proton data sample corresponding to an integrated luminosity of 20.2 fb−1 collected at a centre-of-mass energy √? = 8 TeV. Integrated fiducial cross-sections together with normalised differential fiducial cross-sections, sensitive to the kinematics of final-state QED radiation, are obtained. The results are found to be in agreement with state-of-the-art predictions for final-state QED radiation. First measurements of ?→???? decays are also reported.
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| 14. |
- Alasfar, Lina, et al.
(författare)
-
Effective Field Theory descriptions of Higgs boson pair production
- 2024
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Higgs boson pair production is traditionally considered to be of particular interest for a measurement of the trilinear Higgs self-coupling. Yet it can offer insights into other couplings as well, since - in an effective field theory (EFT) parameterisation of potential new physics - both the production cross section and kinematical properties of the Higgs boson pair depend on various other Wilson coefficients of EFT operators. This note summarises the ongoing efforts related to the development of EFT tools for Higgs boson pair production in gluon fusion, and provides recommendations for the use of distinct EFT parameterisations in the Higgs boson pair production process. This document also outlines where further efforts are needed and provides a detailed analysis of theoretical uncertainties. Additionally, benchmark scenarios are updated. We also re-derive a parameterisation of the next-to-leading order (NLO) QCD corrections in terms of the EFT Wilson coefficients both for the total cross section and the distribution in the invariant mass of the Higgs boson pair, providing for the first time also the covariance matrix. A reweighting procedure making use of the newly derived coefficients is validated, which can be used to significantly speed up experimental analyses.
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| 15. |
- Andrean, Stefio Y., 1991-, et al.
(författare)
-
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
-
Ingår i: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 849
-
Tidskriftsartikel (refereegranskat)abstract
- The CP properties of the coupling between the Higgs boson and the top quark are investigated using 139 fb−1 of proton–proton collision data recorded by the ATLAS experiment at the LHC at a centre-of-mass energy of s√=13?=13 TeV. The CP structure of the top quark–Higgs boson Yukawa coupling is probed in events with a Higgs boson decaying into a pair of b-quarks and produced in association with either a pair of top quarks, tt¯H??¯?, or a single top quark, tH. Events containing one or two electrons or muons are used for the measurement. Multivariate techniques are used to select regions enriched in tt¯H??¯? and tH events, where dedicated CP-sensitive observables are exploited. In an extension of the Standard Model (SM) with a CP-odd admixture in the top–Higgs Yukawa coupling, the mixing angle between CP-even and CP-odd couplings is measured to be α=11∘+52∘−73∘?=11−73∘∘+52∘, compatible with the SM prediction corresponding to α=0?=0.
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| 16. |
- Dimitriadi, Christina
(författare)
-
Double Higgs τrouble : Searches for Higgs boson pairs in the ATLAS experiment and their interpretations
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the discovery of the Higgs boson by the ATLAS and CMS experiments at the Large Hadron Collider (LHC), extensive measurements of its properties have confirmed the predictions of the Standard Model (SM). However, the Higgs boson self-coupling, which is related to the shape of the Higgs potential, still remains loosely constrained experimentally. Searches for the production of Higgs boson pairs (HH) are of great interest, especially for measuring the Higgs boson self-coupling. While the SM predicts a very small event rate for this process, modifications of the Higgs boson self-coupling or new couplings introduced in effective field theories (EFTs) can lead to enhancements of the HH cross-section. This thesis focuses on searches for, and interpretations of, non-resonant Higgs boson pair production in the final state with two b-quarks and two τ-leptons using 140 fb-1 of proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the ATLAS experiment. This final state offers a sizeable branching ratio and moderate background rates, making it one of the most appealing search channels for HH production. No statistically significant signal excess is found above the expected background, therefore upper limits are set on the HH signal strength. The search yields an observed (expected) upper limit of 5.9 (3.3) times the SM cross-section prediction at 95% confidence level. In turn, the ratio of the Higgs boson self-coupling to its SM value, κλ, is constrained to an observed (expected) 95% confidence interval of [-3.1, 9.0] ([-2.5, 9.3]). The results are also interpreted within two distinct EFT frameworks, the Higgs EFT (HEFT) and Standard Model EFT (SMEFT), through constraints on the respective Wilson coefficients and upper limits on the HH cross-section for seven HEFT shape benchmarks with representative features in the HH invariant mass spectrum. Looking forward, the sensitivity of the search is explored at the High-Luminosity LHC by extrapolating the results to 14 TeV and 3000 fb-1. The projected signal significance assuming SM kinematics reaches 2.8σ, while κλ is expected to be constrained to the 2σ confidence interval [-0.3, 7.4].
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| 17. |
- Mullier, Geoffrey A., et al.
(författare)
-
Differential cross-section measurements of the production of four charged leptons in association with two jets using the ATLAS detector
- 2024
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2024:1
-
Tidskriftsartikel (refereegranskat)abstract
- Differential cross-sections are measured for the production of four charged leptons in association with two jets. These measurements are sensitive to final states in which the jets are produced via the strong interaction as well as to the purely-electroweak vector boson scattering process. The analysis is performed using proton-proton collision data collected by ATLAS at s√ = 13 TeV and with an integrated luminosity of 140 fb−1. The data are corrected for the effects of detector inefficiency and resolution and are compared to state-of-the-art Monte Carlo event generator predictions. The differential cross-sections are used to search for anomalous weak-boson self-interactions that are induced by dimension-six and dimension-eight operators in Standard Model effective field theory.
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| 18. |
- Mullier, Geoffrey A., et al.
(författare)
-
Differential cross-section measurements of the production of four charged leptons in association with two jets using the ATLAS detector
- 2024
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer Nature. - 1126-6708 .- 1029-8479. ; 2024:1
-
Tidskriftsartikel (refereegranskat)abstract
- Differential cross-sections are measured for the production of four charged leptons in association with two jets. These measurements are sensitive to final states in which the jets are produced via the strong interaction as well as to the purely-electroweak vector boson scattering process. The analysis is performed using proton-proton collision data collected by ATLAS at √s = 13 TeV and with an integrated luminosity of 140 fb−1. The data are corrected for the effects of detector inefficiency and resolution and are compared to state-of-the-art Monte Carlo event generator predictions. The differential cross-sections are used to search for anomalous weak-boson self-interactions that are induced by dimension-six and dimension-eight operators in Standard Model effective field theory.
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| 19. |
- Mullier, Geoffrey A., et al.
(författare)
-
Measurement of the Centrality Dependence of the Dijet Yield in p+Pb Collisions at √sNN=8.16 TeV with the ATLAS Detector
- 2024
-
Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 132:10
-
Tidskriftsartikel (refereegranskat)abstract
- ATLAS measured the centrality dependence of the dijet yield using 165 nb−1 of p+Pb data collected at √sNN=8.16 TeV in 2016. The event centrality, which reflects the p+Pb impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, RCP, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The RCP shows a scaling with the Bjorken x of the parton originating from the proton, xp, while no such trend is observed as a function of xPb. This analysis provides unique input to understanding the role of small proton spatial configurations in p+Pb collisions by covering parton momentum fractions from the valence region down to xp∼10−3 and xPb∼4×10−4.
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| 20. |
- Mullier, Geoffrey A., et al.
(författare)
-
Observation of Wγγ triboson production in proton-proton collisions at √s = 13 TeV with the ATLAS detector
- 2024
-
Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 848
-
Tidskriftsartikel (refereegranskat)abstract
- This letter reports the observation of W(ℓν)γγ production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of s√=13 TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb−1. Events with a leptonically-decaying W boson and at least two photons are considered. The background-only hypothesis is rejected with an observed and expected significance of 5.6 standard deviations. The inclusive fiducial production cross section of W(eν)γγ and W(μν)γγ events is measured to be σfid=13.8±1.1(stat)+2.1−2.0(syst)±0.1(lumi) fb, in agreement with the Standard Model prediction.
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| 21. |
- Mullier, Geoffrey A., et al.
(författare)
-
Observation of Wγγ triboson production in proton-proton collisions at √s=13 TeV with the ATLAS detector
- 2024
-
Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 848
-
Tidskriftsartikel (refereegranskat)abstract
- This letter reports the observation of ? (??)?? production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of √s=13 TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb−1. Events with a leptonically-decaying W boson and at least two photons are considered. The background-only hypothesis is rejected with an observed and expected significance of 5.6 standard deviations. The inclusive fiducial production cross section of f ? (??)?? and ? (??)?? events is measured to be σfid= fb, in agreement with the Standard Model prediction.
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| 22. |
- Mullier, Geoffrey A., et al.
(författare)
-
Search for non-resonant production of semi-visible jets using Run 2 data in ATLAS
- 2024
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 848
-
Tidskriftsartikel (refereegranskat)abstract
- Semi-visible jets, with a significant contribution to the event's missing transverse momentum, can arise in strongly interacting dark sectors. This results in an event topology where one of the jets can be aligned with the direction of the missing transverse momentum. The first search for semi-visible jets produced via a t-channel mediator exchange is presented. The analysis uses proton-proton collisions with an integrated luminosity of 139 fb−1 and a centre-of-mass energy of 13 TeV, collected with the ATLAS detector during the Run 2 of the LHC. No excess over Standard Model predictions is observed. Assuming a coupling strength of unity between the mediator, a Standard Model quark and a dark quark, mediator masses up to 2.7 TeV are excluded at the 95% confidence level. Upper limits on the coupling strength are also derived.
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| 23. |
- Mullier, Geoffrey A., et al.
(författare)
-
Search for the decay of the Higgs boson to a Z boson and a light pseudoscalar particle decaying to two photons
- 2024
-
Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 850
-
Tidskriftsartikel (refereegranskat)abstract
- A search for the decay of the Higgs boson to a ? boson and a light, pseudoscalar particle, ?, decaying respectively to two leptons and to two photons is reported. The search uses the full LHC Run 2 proton–proton collision data at √? = 13 TeV, corresponding to 139 fb−1 collected by the ATLAS detector. This is one of the first searches for this specific decay mode of the Higgs boson, and it probes unexplored parameter space in models with axion-likeparticles (ALPs) and extended scalar sectors. The mass of the ? particle is assumed to be in the range 0.1–33 GeV. The data are analysed in two categories: a merged category where the photons from the ? decay are reconstructedin the ATLAS calorimeter as a single cluster, and a resolved category in which two separate photons are detected. The main background processes are from Standard Model ? boson production in association with photons orjets. The data are in agreement with the background predictions, and upper limits on the branching ratio of the Higgs boson decay to ?? times the branching ratio ? → ?? are derived at the 95% confidence level and theyrange from 0.08% to 2% depending on the mass of the ? particle. The results are also interpreted in the contextof ALP models.
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| 24. |
- Mullier, Geoffrey A., et al.
(författare)
-
Search for the decay of the Higgs boson to a Z boson and a light pseudoscalar particle decaying to two photons
- 2024
-
Ingår i: Physics Letters B. - : Elsevier B.V.. - 0370-2693 .- 1873-2445. ; 850
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Tidskriftsartikel (refereegranskat)abstract
- A search for the decay of the Higgs boson to a Z boson and a light, pseudoscalar particle, a, decaying respectively to two leptons and to two photons is reported. The search uses the full LHC Run 2 proton–proton collision data at √?=13 TeV, corresponding to 139 fb−1 collected by the ATLAS detector. This is one of the first searches for this specific decay mode of the Higgs boson, and it probes unexplored parameter space in models with axion-like particles (ALPs) and extended scalar sectors. The mass of the a particle is assumed to be in the range 0.1–33 GeV. The data are analysed in two categories: a merged category where the photons from the a decay are reconstructed in the ATLAS calorimeter as a single cluster, and a resolved category in which two separate photons are detected. The main background processes are from Standard Model Z boson production in association with photons or jets. The data are in agreement with the background predictions, and upper limits on the branching ratio of the Higgs boson decay to Za times the branching ratio ?→?? are derived at the 95% confidence level and they range from 0.08% to 2% depending on the mass of the a particle. The results are also interpreted in the context of ALP models.
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