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Aad, G., Leroy, C., Lund-Jensen, B., Luongo, N. A., Oide, H., Shahinian, J. D., . . . et al., . (2024). Electron and photon energy calibration with the ATLAS detector using LHC Run 2 data. Journal of Instrumentation, 19(2), Article ID P02009.
Open this publication in new window or tab >>Electron and photon energy calibration with the ATLAS detector using LHC Run 2 data
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2024 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 19, no 2, article id P02009Article in journal (Refereed) Published
Abstract [en]

This paper presents the electron and photon energy calibration obtained with the ATLAS detector using 140 fb−1 of LHC proton-proton collision data recorded at √s = 13 TeV between 2015 and 2018. Methods for the measurement of electron and photon energies are outlined, along with the current knowledge of the passive material in front of the ATLAS electromagnetic calorimeter. The energy calibration steps are discussed in detail, with emphasis on the improvements introduced in this paper. The absolute energy scale is set using a large sample of Z-boson decays into electron-positron pairs, and its residual dependence on the electron energy is used for the first time to further constrain systematic uncertainties. The achieved calibration uncertainties are typically 0.05% for electrons from resonant Z-boson decays, 0.4% at ET ∼ 10 GeV, and 0.3% at ET ∼ 1 TeV; for photons at ET ∼ 60 GeV, they are 0.2% on average. This is more than twice as precise as the previous calibration. The new energy calibration is validated using J/ → ee and radiative Z-boson decays.

Place, publisher, year, edition, pages
Institute of Physics, 2024
Keywords
calibration, Calorimeter methods; Pattern recognition, cluster finding, fitting methods; Performance of High Energy Physics Detectors
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-344206 (URN)10.1088/1748-0221/19/02/P02009 (DOI)2-s2.0-85185886671 (Scopus ID)
Note

QC 20240308

Available from: 2024-03-06 Created: 2024-03-06 Last updated: 2024-03-08Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . et al., . (2024). Measurement of the H→ γγ and H→ ZZ<sup>∗</sup>→ 4 ℓ cross-sections in pp collisions at √s=13.6 TeV with the ATLAS detector. European Physical Journal C, 84(1), Article ID 78.
Open this publication in new window or tab >>Measurement of the H→ γγ and H→ ZZ<sup>∗</sup>→ 4 ℓ cross-sections in pp collisions at √s=13.6 TeV with the ATLAS detector
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2024 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 84, no 1, article id 78Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Institute for Ionics, 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-342828 (URN)10.1140/epjc/s10052-023-12130-5 (DOI)2-s2.0-85183047904 (Scopus ID)
Note

QC 20240206

Available from: 2024-01-31 Created: 2024-01-31 Last updated: 2024-02-06Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . Zwalinski, L. (2024). Measurement of the ttcross section and its ratio to the Z production cross √section using pp collisions at √s=13.6 TeV with the ATLAS detector. Physics Letters B, 848, Article ID 138376.
Open this publication in new window or tab >>Measurement of the ttcross section and its ratio to the Z production cross √section using pp collisions at √s=13.6 TeV with the ATLAS detector
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2024 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 848, article id 138376Article in journal (Refereed) Published
Abstract [en]

The inclusive top-quark-pair production cross section rrtt and its ratio to the Z-boson production cross section have been measured in proton-proton collisions at root s = 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 b-tagged jets, and assuming Standard Model decays, the top-quark-pair production cross section is measured to be rrtt = 850 +/- 3(stat.) +/- 18(syst.) +/- 20(lumi.) pb. The ratio of the ttand the Z-boson production cross sections is also measured, where the Z-boson contribution is determined for inclusive e+e- and mu+mu- events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the ttcross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, Rtt/Z = 1.145 +/- 0.003(stat.) +/- 0.021(syst.) +/- 0.002(lumi.) is consistent with the Standard Model prediction using the PDF4LHC21 PDF set.

Place, publisher, year, edition, pages
Elsevier, 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-343039 (URN)10.1016/j.physletb.2023.138376 (DOI)001136441300001 ()2-s2.0-85183680739 (Scopus ID)
Note

QC 20240209

Available from: 2024-02-09 Created: 2024-02-09 Last updated: 2024-02-15Bibliographically approved
Aad, G., Lund-Jensen, B., Ohm, C., Strandberg, J., Zwalinski, L. & et al., . (2024). Observation of WZγ Production in pp Collisions at sqrt[s]=13  TeV with the ATLAS Detector. Physical Review Letters, 132(2), 21802
Open this publication in new window or tab >>Observation of WZγ Production in pp Collisions at sqrt[s]=13  TeV with the ATLAS Detector
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2024 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 132, no 2, p. 21802-Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
NA, 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-343197 (URN)10.1103/PhysRevLett.132.021802 (DOI)38277610 (PubMedID)2-s2.0-85184667847 (Scopus ID)
Note

QC 20240209

Available from: 2024-02-08 Created: 2024-02-08 Last updated: 2024-02-22Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . et al., . (2024). Performance and calibration of quark/gluon-jet taggers using 140 fb<sup>−1</sup> of pp collisions at √s = 13 TeV with the ATLAS detector. Chinese Physics C, 48(2), Article ID 023001.
Open this publication in new window or tab >>Performance and calibration of quark/gluon-jet taggers using 140 fb<sup>−1</sup> of pp collisions at √s = 13 TeV with the ATLAS detector
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2024 (English)In: Chinese Physics C, ISSN 1674-1137, E-ISSN 2058-6132, Vol. 48, no 2, article id 023001Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
IOP Publishing, 2024
Keywords
ATLAS, GLUON, JET, QUARK, TAGGING
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-344021 (URN)10.1088/1674-1137/acf701 (DOI)2-s2.0-85185169176 (Scopus ID)
Note

QC 20240229

Available from: 2024-02-28 Created: 2024-02-28 Last updated: 2024-02-29Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., . . . et al., . (2024). 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. Physics Letters B, 849, Article ID 138469.
Open this publication in new window or tab >>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
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2024 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 849, article id 138469Article in journal (Refereed) Published
Abstract [en]

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 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=11−73∘∘+52∘, compatible with the SM prediction corresponding to α=0.

Place, publisher, year, edition, pages
Elsevier B.V., 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-344008 (URN)10.1016/j.physletb.2024.138469 (DOI)2-s2.0-85185283920 (Scopus ID)
Note

QC 20240229

Available from: 2024-02-28 Created: 2024-02-28 Last updated: 2024-02-29Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Ripellino, G., . . . et al., . (2024). Search for New Phenomena in Two-Body Invariant Mass Distributions Using Unsupervised Machine Learning for Anomaly Detection at √s = 13 TeV with the ATLAS Detector. Physical Review Letters, 132(8), Article ID 081801.
Open this publication in new window or tab >>Search for New Phenomena in Two-Body Invariant Mass Distributions Using Unsupervised Machine Learning for Anomaly Detection at √s = 13 TeV with the ATLAS Detector
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2024 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 132, no 8, article id 081801Article in journal (Refereed) Published
Abstract [en]

Searches for new resonances are performed using an unsupervised anomaly-detection technique. Events with at least one electron or muon are selected from 140 fb−1 of pp collisions at √s ¼ 13 TeV recorded by ATLAS at the Large Hadron Collider. The approach involves training an autoencoder on data, and subsequently defining anomalous regions based on the reconstruction loss of the decoder. Studies focus on nine invariant mass spectra that contain pairs of objects consisting of one light jet or b jet and either one lepton (e; μ), photon, or second light jet or b jet in the anomalous regions. No significant deviations from the background hypotheses are observed. Limits on contributions from generic Gaussian signals with various widths of the resonance mass are obtained for nine invariant masses in the anomalous regions.

Place, publisher, year, edition, pages
American Physical Society, 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-344327 (URN)10.1103/PhysRevLett.132.081801 (DOI)2-s2.0-85186742137 (Scopus ID)
Note

QC 20240314

Available from: 2024-03-13 Created: 2024-03-13 Last updated: 2024-03-14Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . et al., . (2024). Search for non-resonant production of semi-visible jets using Run 2 data in ATLAS. Physics Letters B, 848, Article ID 138324.
Open this publication in new window or tab >>Search for non-resonant production of semi-visible jets using Run 2 data in ATLAS
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2024 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 848, article id 138324Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier BV, 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-343373 (URN)10.1016/j.physletb.2023.138324 (DOI)001127436800001 ()
Note

QC 20240212

Available from: 2024-02-12 Created: 2024-02-12 Last updated: 2024-02-12Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . et al., . (2024). Search for the decay of the Higgs boson to a Z boson and a light pseudoscalar particle decaying to two photons. Physics Letters B, 850, Article ID 138536.
Open this publication in new window or tab >>Search for the decay of the Higgs boson to a Z boson and a light pseudoscalar particle decaying to two photons
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2024 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 850, article id 138536Article in journal (Refereed) Published
Abstract [en]

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 s=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 a→γγ 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.

Place, publisher, year, edition, pages
Elsevier B.V., 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-344331 (URN)10.1016/j.physletb.2024.138536 (DOI)2-s2.0-85186584048 (Scopus ID)
Note

QC 20240314

Available from: 2024-03-13 Created: 2024-03-13 Last updated: 2024-03-14Bibliographically approved
Aad, G., Leopold, A., Lokajicek, M., Lundberg, O., Lund-Jensen, B., Ohm, C., . . . Zwalinski, L. (2024). Studies of new Higgs boson interactions through nonresonant HH production in the b(b)over-barγγ final state in pp collisions at √s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP), 2024(1), Article ID 66.
Open this publication in new window or tab >>Studies of new Higgs boson interactions through nonresonant HH production in the b(b)over-barγγ final state in pp collisions at √s=13 TeV with the ATLAS detector
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2024 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2024, no 1, article id 66Article in journal (Refereed) Published
Abstract [en]

A search for nonresonant Higgs boson pair production in the b (b) over bar gamma gamma 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 kappa(lambda) but also of the quartic HHVV (V = W, Z) coupling modifier kappa(2V). No significant excess above the expected background from Standard Model processes is observed. An observed upper limit mu(HH) < 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 < kappa(lambda) < 6.9 and -0.5 < kappa(2V) < 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.

Place, publisher, year, edition, pages
Springer Nature, 2024
Keywords
Hadron-Hadron Scattering, Higgs Physics
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-344490 (URN)10.1007/JHEP01(2024)066 (DOI)001147783600001 ()
Note

QC 20240318

Available from: 2024-03-18 Created: 2024-03-18 Last updated: 2024-03-18Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-8913-0981

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