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Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . et al., . (2025). Combination of searches for singly and doubly charged Higgs bosons produced via vector-boson fusion in proton–proton collisions at s=13 TeV with the ATLAS detector. Physics Letters B, 860, Article ID 139137.
Open this publication in new window or tab >>Combination of searches for singly and doubly charged Higgs bosons produced via vector-boson fusion in proton–proton collisions at s=13 TeV with the ATLAS detector
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2025 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 860, article id 139137Article in journal (Refereed) Published
Abstract [en]

A combination of searches for singly and doubly charged Higgs bosons, H± and H±±, produced via vector-boson fusion is performed using 140 fb−1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, collected with the ATLAS detector during Run 2 of the Large Hadron Collider. Searches targeting decays to massive vector bosons in leptonic final states (electrons or muons) are considered. New constraints are reported on the production cross-section times branching fraction for charged Higgs boson masses between 200 GeV and 3000 GeV. The results are interpreted in the context of the Georgi-Machacek model for which the most stringent constraints to date are set for the masses considered in the combination.

Place, publisher, year, edition, pages
Elsevier BV, 2025
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-357674 (URN)10.1016/j.physletb.2024.139137 (DOI)001381473400001 ()2-s2.0-85210762616 (Scopus ID)
Note

QC 20241213

Available from: 2024-12-12 Created: 2024-12-12 Last updated: 2025-02-03Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C. C., Shaheen, R., . . . et al., . (2025). Measurement of top-quark pair production in association with charm quarks in proton–proton collisions at s=13 TeV with the ATLAS detector. Physics Letters B, 860, Article ID 139177.
Open this publication in new window or tab >>Measurement of top-quark pair production in association with charm quarks in proton–proton collisions at s=13 TeV with the ATLAS detector
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2025 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 860, article id 139177Article in journal (Refereed) Published
Abstract [en]

Inclusive cross-sections for top-quark pair production in association with charm quarks are measured with proton–proton collision data at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 140 fb−1, collected with the ATLAS experiment at the LHC between 2015 and 2018. The measurements are performed by requiring one or two charged leptons (electrons and muons), two b-tagged jets, and at least one additional jet in the final state. A custom flavor-tagging algorithm is employed for the simultaneous identification of b-jets and c-jets. In a fiducial phase space that replicates the acceptance of the ATLAS detector, the cross-sections for tt¯+≥2c and tt¯+1c production are measured to be 1.28−0.24+0.27pb and 6.4−0.9+1.0pb, respectively. The measurements are primarily limited by uncertainties in the modeling of inclusive tt¯ and tt¯+bb¯ production, in the calibration of the flavor-tagging algorithm, and by data statistics. Cross-section predictions from various tt¯ simulations are largely consistent with the measured cross-section values, though all underpredict the observed values by 0.5 to 2.0 standard deviations. In a phase-space volume without requirements on the tt¯ decay products and the jet multiplicity, the cross-section ratios of tt¯+≥2c and tt¯+1c to total tt¯+jets production are determined to be (1.23±0.25)% and (8.8±1.3)%.

Place, publisher, year, edition, pages
Elsevier BV, 2025
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-357939 (URN)10.1016/j.physletb.2024.139177 (DOI)2-s2.0-85211336127 (Scopus ID)
Note

QC 20241219

Available from: 2024-12-19 Created: 2024-12-19 Last updated: 2024-12-19Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . et al., . (2024). A precise measurement of the Z-boson double-differential transverse momentum and rapidity distributions in the full phase space of the decay leptons with the ATLAS experiment at s=8 TeV. European Physical Journal C, 84(3), Article ID 315.
Open this publication in new window or tab >>A precise measurement of the Z-boson double-differential transverse momentum and rapidity distributions in the full phase space of the decay leptons with the ATLAS experiment at s=8 TeV
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2024 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 84, no 3, article id 315Article in journal (Refereed) Published
Abstract [en]

This paper presents for the first time a precise measurement of the production properties of the Z boson in the full phase space of the decay leptons. This is in contrast to the many previous precise unfolded measurements performed in the fiducial phase space of the decay leptons. The measurement is obtained from proton–proton collision data collected by the ATLAS experiment in 2012 at s=8 TeV at the LHC and corresponding to an integrated luminosity of 20.2 fb-1. The results, based on a total of 15.3 million Z-boson decays to electron and muon pairs, extend and improve a previous measurement of the full set of angular coefficients describing Z-boson decay. The double-differential cross-section distributions in Z-boson transverse momentum pT and rapidity y are measured in the pole region, defined as 80<mℓℓ<100 GeV, over the range |y|<3.6. The total uncertainty of the normalised cross-section measurements in the peak region of the pT distribution is dominated by statistical uncertainties over the full range and increases as a function of rapidity from 0.5–1.0% for |y|<2.0 to 2-7% at higher rapidities. The results for the rapidity-dependent transverse momentum distributions are compared to state-of-the-art QCD predictions, which combine in the best cases approximate N4LL resummation with N3LO fixed-order perturbative calculations. The differential rapidity distributions integrated over pT are even more precise, with accuracies from 0.2–0.3% for |y|<2.0 to 0.4–0.9% at higher rapidities, and are compared to fixed-order QCD predictions using the most recent parton distribution functions. The agreement between data and predictions is quite good in most cases.

Place, publisher, year, edition, pages
Springer Nature, 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-346172 (URN)10.1140/epjc/s10052-024-12438-w (DOI)001253017600003 ()2-s2.0-85190755857 (Scopus ID)
Note

QC 20241104

Available from: 2024-05-03 Created: 2024-05-03 Last updated: 2024-11-04Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . et al., . (2024). A search for top-squark pair production, in final states containing a top quark, a charm quark and missing transverse momentum, using the 139 fb−1 of pp collision data collected by the ATLAS detector. Journal of High Energy Physics (JHEP), 2024(7), Article ID 250.
Open this publication in new window or tab >>A search for top-squark pair production, in final states containing a top quark, a charm quark and missing transverse momentum, using the 139 fb1 of pp collision data collected by 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 7, article id 250Article in journal (Refereed) Published
Abstract [en]

This paper presents a search for top-squark pair production in final states with a top quark, a charm quark and missing transverse momentum. The data were collected with the ATLAS detector during LHC Run 2 and correspond to an integrated luminosity of 139 fb−1 of proton-proton collisions at a centre-of-mass energy of s = 13 TeV. The analysis is motivated by an extended Minimal Supersymmetric Standard Model featuring a non-minimal flavour violation in the second- and third-generation squark sector. The top squark in this model has two possible decay modes, either t~1→cχ~10 or t~1→tχ~10, where the χ~10 is undetected. The analysis is optimised assuming that both of the decay modes are equally probable, leading to the most likely final state of tc+ETmiss. Good agreement is found between the Standard Model expectation and the data in the search regions. Exclusion limits at 95% CL are obtained in the mt~1 vs. mχ~10 plane and, in addition, limits on the branching ratio of the t~1→tχ~10 decay as a function of m(t~1) are also produced. Top-squark masses of up to 800 GeV are excluded for scenarios with light neutralinos, and top-squark masses up to 600 GeV are excluded in scenarios where the neutralino and the top squark are almost mass degenerate.

Place, publisher, year, edition, pages
Springer Nature, 2024
Keywords
Beyond Standard Model, Hadron-Hadron Scattering, Supersymmetry
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-351895 (URN)10.1007/JHEP07(2024)250 (DOI)2-s2.0-85200565461 (Scopus ID)
Note

QC 20240823

Available from: 2024-08-19 Created: 2024-08-19 Last updated: 2024-08-23Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . et al., . (2024). Accuracy versus precision in boosted top tagging with the ATLAS detector. Journal of Instrumentation, 19(8), Article ID P08018.
Open this publication in new window or tab >>Accuracy versus precision in boosted top tagging with the ATLAS detector
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2024 (English)In: Journal of Instrumentation, E-ISSN 1748-0221, Vol. 19, no 8, article id P08018Article in journal (Refereed) Published
Abstract [en]

The identification of top quark decays where the top quark has a large momentum transverse to the beam axis, known as top tagging, is a crucial component in many measurements of Standard Model processes and searches for beyond the Standard Model physics at the Large Hadron Collider. Machine learning techniques have improved the performance of top tagging algorithms, but the size of the systematic uncertainties for all proposed algorithms has not been systematically studied. This paper presents the performance of several machine learning based top tagging algorithms on a dataset constructed from simulated proton-proton collision events measured with the ATLAS detector at √s = 13 TeV. The systematic uncertainties associated with these algorithms are estimated through an approximate procedure that is not meant to be used in a physics analysis, but is appropriate for the level of precision required for this study. The most performant algorithms are found to have the largest uncertainties, motivating the development of methods to reduce these uncertainties without compromising performance. To enable such efforts in the wider scientific community, the datasets used in this paper are made publicly available.

Place, publisher, year, edition, pages
Institute of Physics, 2024
Keywords
Analysis and statistical methods, Performance of High Energy Physics Detectors
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-353433 (URN)10.1088/1748-0221/19/08/P08018 (DOI)2-s2.0-85203388592 (Scopus ID)
Note

QC 20240925

Available from: 2024-09-19 Created: 2024-09-19 Last updated: 2024-09-25Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . et al., . (2024). ATLAS Run 2 searches for electroweak production of supersymmetric particles interpreted within the pMSSM. Journal of High Energy Physics (JHEP), 2024(5), Article ID 106.
Open this publication in new window or tab >>ATLAS Run 2 searches for electroweak production of supersymmetric particles interpreted within the pMSSM
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2024 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2024, no 5, article id 106Article in journal (Refereed) Published
Abstract [en]

A summary of the constraints from searches performed by the ATLAS collaboration for the electroweak production of charginos and neutralinos is presented. Results from eight separate ATLAS searches are considered, each using 140 fb−1 of proton-proton data at a centre-of-mass energy of s = 13 TeV collected at the Large Hadron Collider during its second data-taking run. The results are interpreted in the context of the 19-parameter phenomenological minimal supersymmetric standard model, where R-parity conservation is assumed and the lightest supersymmetric particle is assumed to be the lightest neutralino. Constraints from previous electroweak, flavour and dark matter related measurements are also considered. The results are presented in terms of constraints on supersymmetric particle masses and are compared with limits from simplified models. Also shown is the impact of ATLAS searches on parameters such as the dark matter relic density and the spin-dependent and spin-independent scattering cross-sections targeted by direct dark matter detection experiments. The Higgs boson and Z boson ‘funnel regions’, where a low-mass neutralino would not oversaturate the dark matter relic abundance, are almost completely excluded by the considered constraints. Example spectra for non-excluded supersymmetric models with light charginos and neutralinos are also presented.

Place, publisher, year, edition, pages
Springer Science and Business Media Deutschland GmbH, 2024
Keywords
Beyond Standard Model, Hadron-Hadron Scattering, Supersymmetry
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-356672 (URN)10.1007/JHEP05(2024)106 (DOI)001280063500001 ()2-s2.0-85208419299 (Scopus ID)
Note

QC 20241121

Available from: 2024-11-20 Created: 2024-11-20 Last updated: 2024-11-21Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . Zwalinski, L. (2024). Azimuthal Angle Correlations of Muons Produced via Heavy-Flavor Decays in 5.02 TeV Pb + Pb and pp Collisions with the ATLAS Detector. Physical Review Letters, 132(20), Article ID 202301.
Open this publication in new window or tab >>Azimuthal Angle Correlations of Muons Produced via Heavy-Flavor Decays in 5.02 TeV Pb + Pb and pp Collisions with the ATLAS Detector
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2024 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 132, no 20, article id 202301Article in journal (Refereed) Published
Abstract [en]

Angular correlations between heavy quarks provide a unique probe of the quark-gluon plasma created in ultrarelativistic heavy-ion collisions. Results are presented of a measurement of the azimuthal angle correlations between muons originating from semileptonic decays of heavy quarks produced in 5.02 TeV Pb + Pb and pp collisions at the LHC. The muons are measured with transverse momenta and pseudorapidities satisfying p(T)(mu) > 4 GeV and vertical bar eta(mu)vertical bar < 2.4, respectively. The distributions of azimuthal angle separation Delta Phi for muon pairs having pseudorapidity separation vertical bar Delta eta vertical bar > 0.8, are measured in different Pb + Pb centrality intervals and compared to the same distribution measured in pp collisions at the same center-of-mass energy. Results are presented separately for muon pairs with opposite-sign charges, same-sign charges, and all pairs. A clear peak is observed in all Delta Phi distributions at Delta Phi similar to Pi, consistent with the parent heavy-quark pairs being produced via hard-scattering processes. The widths of that peak, characterized using Cauchy-Lorentz fits to the Delta Phi distributions, are found to not vary significantly as a function of Pb + Pb collision centrality and are similar for pp and Pb + Pb collisions. This observation will provide important constraints on theoretical descriptions of heavy-quark interactions with the quarkgluon plasma.

Place, publisher, year, edition, pages
American Physical Society (APS), 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-355823 (URN)10.1103/PhysRevLett.132.202301 (DOI)001271839000001 ()38829073 (PubMedID)2-s2.0-85193942982 (Scopus ID)
Note

QC 20241105

Available from: 2024-11-05 Created: 2024-11-05 Last updated: 2024-11-05Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . Zwalinski, L. (2024). Beam-induced backgrounds measured in the ATLAS detector during local gas injection into the LHC beam vacuum. Journal of Instrumentation, 19(6)
Open this publication in new window or tab >>Beam-induced backgrounds measured in the ATLAS detector during local gas injection into the LHC beam vacuum
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2024 (English)In: Journal of Instrumentation, E-ISSN 1748-0221, Vol. 19, no 6Article in journal (Refereed) Published
Abstract [en]

Inelastic beam-gas collisions at the Large Hadron Collider (LHC), within a few hundred metres of the ATLAS experiment, are known to give the dominant contribution to beam backgrounds. These are monitored by ATLAS with a dedicated Beam Conditions Monitor (BCM) and with the rate of fake jets in the calorimeters. These two methods are complementary since the BCM probes backgrounds just around the beam pipe while fake jets are observed at radii of up to several metres. In order to quantify the correlation between the residual gas density in the LHC beam vacuum and the experimental backgrounds recorded by ATLAS, several dedicated tests were performed during LHC Run 2. Local pressure bumps, with a gas density several orders of magnitude higher than during normal operation, were introduced at different locations. The changes of beam-related backgrounds, seen in ATLAS, are correlated with the local pressure variation. In addition the rates of beam-gas events are estimated from the pressure measurements and pressure bump profiles obtained from calculations. Using these rates, the efficiency of the ATLAS beam background monitors to detect beam-gas events is derived as a function of distance from the interaction point. These efficiencies and characteristic distributions of fake jets from the beam backgrounds are found to be in good agreement with results of beam-gas simulations performed with the Fluka Monte Carlo programme.

Place, publisher, year, edition, pages
IOP Publishing Ltd, 2024
Keywords
Accelerator modelling and simulations (multi-particle dynamics, single-particle dynamics), Performance of High Energy Physics Detectors, Radiation calculations
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-358701 (URN)10.1088/1748-0221/19/06/P06014 (DOI)001287367200001 ()2-s2.0-85196151175 (Scopus ID)
Note

QC 20250121

Available from: 2025-01-21 Created: 2025-01-21 Last updated: 2025-01-21Bibliographically approved
Aad, G., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . et al., . (2024). Calibration of a soft secondary vertex tagger using proton-proton collisions at √𝑠 =13  TeV with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 110(3), Article ID 032015.
Open this publication in new window or tab >>Calibration of a soft secondary vertex tagger using proton-proton collisions at √𝑠 =13  TeV with the ATLAS detector
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2024 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 110, no 3, article id 032015Article in journal (Refereed) Published
Abstract [en]

Several processes studied by the ATLAS experiment at the Large Hadron Collider produce low-momentum 𝑏-flavored hadrons in the final state. This paper describes the calibration of a dedicated tagging algorithm that identifies 𝑏-flavored hadrons outside of hadronic jets by reconstructing the soft secondary vertices originating from their decays. The calibration is based on a proton-proton collision dataset at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 140  fb−1. Scale factors used to correct the algorithm’s performance in simulated events are extracted for the 𝑏-tagging efficiency and the mistag rate of the algorithm using a data sample enriched in 𝑡⁢¯𝑡 events. Several orthogonal measurement regions are defined, binned as a function of the multiplicities of soft secondary vertices and jets containing a 𝑏-flavored hadron in the event. The mistag rate scale factors are estimated separately for events with low and high average numbers of interactions per bunch crossing. The results, which are derived from events with low missing transverse momentum, are successfully validated in a phase space characterized by high missing transverse momentum and therefore are applicable to new physics searches carried out in either phase space regime.

Place, publisher, year, edition, pages
American Physical Society (APS), 2024
National Category
Subatomic Physics Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-353446 (URN)10.1103/PhysRevD.110.032015 (DOI)001375636400001 ()2-s2.0-85203189338 (Scopus ID)
Note

QC 20250214

Available from: 2024-09-19 Created: 2024-09-19 Last updated: 2025-02-14Bibliographically approved
Hayrapetyan, A., Leopold, A., Lundberg, O., Lund-Jensen, B., Ohm, C., Shaheen, R., . . . et al., . (2024). Combination of Measurements of the Top Quark Mass from Data Collected by the ATLAS and CMS Experiments at √𝑠 =7 and 8 TeV. Physical Review Letters, 132(26), Article ID 261902.
Open this publication in new window or tab >>Combination of Measurements of the Top Quark Mass from Data Collected by the ATLAS and CMS Experiments at √𝑠 =7 and 8 TeV
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2024 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 132, no 26, article id 261902Article in journal (Refereed) Published
Abstract [en]

A combination of fifteen top quark mass measurements performed by the ATLAS and CMS experiments at the LHC is presented. The datasets used correspond to an integrated luminosity of up to 5 and 20  fb−1 of proton-proton collisions at center-of-mass energies of 7 and 8 TeV, respectively. The combination includes measurements in top quark pair events that exploit both the semileptonic and hadronic decays of the top quark, and a measurement using events enriched in single top quark production via the electroweak 𝑡 channel. The combination accounts for the correlations between measurements and achieves an improvement in the total uncertainty of 31% relative to the most precise input measurement. The result is 𝑚𝑡=172.52±0.14⁢(stat)±0.30⁢(syst)  GeV, with a total uncertainty of 0.33 GeV.

Place, publisher, year, edition, pages
American Physical Society (APS), 2024
National Category
Subatomic Physics
Identifiers
urn:nbn:se:kth:diva-350693 (URN)10.1103/PhysRevLett.132.261902 (DOI)001290703200001 ()2-s2.0-85197696145 (Scopus ID)
Note

QC 20250217

Available from: 2024-07-17 Created: 2024-07-17 Last updated: 2025-02-17Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-9415-7903

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