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Publications (10 of 931) Show all publications
Backman, F., Bertoli, G., Bohm, C., Carney, R. M. D., Clément, C., Hellman, S., . . . Wallängen, V. (2023). Measurement of the inclusive t¯t production cross section in the lepton+jets channel in pp collisions at √s=7  TeV with the ATLAS detector using support vector machines. Physical Review D: covering particles, fields, gravitation, and cosmology, 108(3), Article ID 032014.
Open this publication in new window or tab >>Measurement of the inclusive t¯t production cross section in the lepton+jets channel in pp collisions at √s=7  TeV with the ATLAS detector using support vector machines
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2023 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 108, no 3, article id 032014Article in journal (Refereed) Published
Abstract [en]

A measurement of the top quark pair-production cross section in the lepton+jets decay channel is presented. It is based on 4.6  fb−1 of √s=7  TeV pp collision data collected during 2011 by the ATLAS experiment at the CERN Large Hadron Collider. A three-class, multidimensional event classifier based on support vector machines is used to differentiate t¯t events from backgrounds. The t¯t production cross section is found to be σt¯t=168.5±0.7(stat) +6.2−5.9(syst) +3.4−3.2(lumi)  pb. The result is consistent with the Standard Model prediction based on QCD calculations at next-to-next-to-leading order.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-223860 (URN)10.1103/PhysRevD.108.032014 (DOI)001063420300001 ()2-s2.0-85173785320 (Scopus ID)
Available from: 2023-11-22 Created: 2023-11-22 Last updated: 2023-11-22Bibliographically approved
Backman, F., Barranco Navarro, L., Bohm, C., Carney, R. M. D., Clement, C., Hellman, S., . . . Wallängen, V. (2021). Measurement of single top-quark production in association with a W boson in the single-lepton channel at root s=8 TeV with the ATLAS detector. European Physical Journal C, 81(8), Article ID 720.
Open this publication in new window or tab >>Measurement of single top-quark production in association with a W boson in the single-lepton channel at root s=8 TeV with the ATLAS detector
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2021 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 81, no 8, article id 720Article in journal (Refereed) Published
Abstract [en]

The production cross-section of a top quark in association with a W boson is measured using proton-proton collisions at root s = 8 TeV. The dataset corresponds to an integrated luminosity of 20.2 fb(-1,) and was collected in 2012 by the ATLAS detector at the Large Hadron Collider at CERN. The analysis is performed in the single-lepton channel. Events are selected by requiring one isolated lepton (electron or muon) and at least three jets. A neural network is trained to separate the tW signal from the dominant t (t) over bar background. The cross-section is extracted from a binned profile maximum-likelihood fit to a two-dimensional discriminant built from the neural-network output and the invariant mass of the hadronically decaying W boson. The measured crosssection is sigma(tW) = 26 +/- 7 pb, in good agreement with the Standard Model expectation.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-197686 (URN)10.1140/epjc/s10052-021-09371-7 (DOI)000683750400006 ()
Available from: 2021-10-14 Created: 2021-10-14 Last updated: 2022-02-25Bibliographically approved
Backman, F., Barranco Navarro, L., Bohm, C., Carney, R. M. D., Clement, C., Hellman, S., . . . Wallängen, V. (2021). Measurement of the CP-violating phase φs in B0s → J/ψφ decays in ATLAS at 13 TeV. European Physical Journal C, 81(4), Article ID 342.
Open this publication in new window or tab >>Measurement of the CP-violating phase φs in B0s → J/ψφ decays in ATLAS at 13 TeV
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2021 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 81, no 4, article id 342Article in journal (Refereed) Published
Abstract [en]

A measurement of the B0s → J/ψφ decay parameters using 80.5 fb −1 of integrated luminosity collected with the ATLAS detector from 13 TeV proton–proton collisions at the LHC is presented. The measured parameters include the CP-violating phase φs, the width differences between the B0s meson mass eigenstates and the average decay width s. The values measured for the physical parameters are combined with those from 19.2 fb −1 of 7 and 8 TeV data, leading to the following: φs = − 0.087 ± 0.036 (stat.) ± 0.021 (syst.) rads = 0.0657 ± 0.0043 (stat.) ± 0.0037 (syst.) ps−1s = 0.6703 ± 0.0014 (stat.) ± 0.0018 (syst.) ps−1

Results for φs and s are also presented as 68% confidence level contours in the φs–s plane. Furthermore the transversity amplitudes and corresponding strong phases are measured. φs and s measurements are in agreement with the Standard Model predictions.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-195415 (URN)10.1140/epjc/s10052-021-09011-0 (DOI)000643913400004 ()
Available from: 2021-08-24 Created: 2021-08-24 Last updated: 2022-02-25Bibliographically approved
Backman, F., Barranco Navarro, L., Bohm, C., Carney, R. M. D., Clement, C., Hellman, S., . . . Wallängen, V. (2021). Measurement of the jet mass in high transverse momentum Z(-> b(b)over-bar)gamma production at root s=13 TeV using the ATLAS detector. Physics Letters B, 812, Article ID 135991.
Open this publication in new window or tab >>Measurement of the jet mass in high transverse momentum Z(-> b(b)over-bar)gamma production at root s=13 TeV using the ATLAS detector
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2021 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 812, article id 135991Article in journal (Refereed) Published
Abstract [en]

The integrated fiducial cross-section and unfolded differential jet mass spectrum of high transverse momentum Z -> b (b) over bar decays are measured in Z gamma events in proton-proton collisions at root s = 13 TeV. The data analysed were collected between 2015 and 2016 with the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 36.1 fb(-1). Photons are required to have a transverse momentum p(T) > 175 GeV. The Z -> b (b) over bar decay is reconstructed using a jet with p(T) > 200 GeV, found with the anti-k(t) R = 1.0 jet algorithm, and groomed to remove soft and wide-angle radiation and to mitigate contributions from the underlying event and additional proton-proton collisions. Two different but related measurements are performed using two jet grooming definitions for reconstructing the Z -> b (b) over bar decay: trimming and soft drop. These algorithms differ in their experimental and phenomenological implications regarding jet mass reconstruction and theoretical precision. To identify Zbosons, b-tagged R = 0.2 track-jets matched to the groomed large-R calorimeter jet are used as a proxy for the b-quarks. The signal yield is determined from fits of the data-driven background templates to the different jet mass distributions for the two grooming methods. Integrated fiducial cross-sections and unfolded jet mass spectra for each grooming method are compared with leading-order theoretical predictions. The results are found to be in good agreement with Standard Model expectations within the current statistical and systematic uncertainties.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-191715 (URN)10.1016/j.physletb.2020.135991 (DOI)000608167600013 ()
Available from: 2021-03-31 Created: 2021-03-31 Last updated: 2022-02-25Bibliographically approved
Backman, F., Bertoli, G., Bohm, C., Carney, R. M. D., Clement, C., Hellman, S., . . . Wallängen, V. (2021). Measurement of the relative B-c(+/-)/B-+/- production cross section with the ATLAS detector at root s=8 TeV. Physical Review D: covering particles, fields, gravitation, and cosmology, 104(1), Article ID 012010.
Open this publication in new window or tab >>Measurement of the relative B-c(+/-)/B-+/- production cross section with the ATLAS detector at root s=8 TeV
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2021 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 104, no 1, article id 012010Article in journal (Refereed) Published
Abstract [en]

The total cross section and differential cross sections for the production of B-c(+/-) mesons, times their branching fraction to J/psi pi(+/-), are measured relative to those for the production of B-+/- mesons, times their branching fraction to J/psi K-+/-. The data used for this study correspond to an integrated luminosity of 20.3 fb(-1) of pp collisions recorded by the ATLAS detector at the Large Hadron Collider in 2012 at a center-of-mass energy of root s = 8 TeV. The measurement is performed differentially in bins of transverse momentum p(T) for 13 GeV < p(T)(B-c(+/-)) < 22 GeV and p(T)(B-c(+/-)) > 22 GeV and in bins of rapidity y for vertical bar y vertical bar < 0.75 and 0.75 < vertical bar y vertical bar < 2.3. The relative cross section times branching fraction for the full range p(T) > 13 GeV and vertical bar y vertical bar < 2.3 is (0.34 +/- 0.04(stat) (+0.06)(-0.02 sys) +/- 0.01(lifetime))%. The differential measurements suggest that the production cross section of the B-c(+/-) decreases faster with p(T) than the production cross section of the B-+/-, while no significant dependence on rapidity is observed.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-197068 (URN)10.1103/PhysRevD.104.012010 (DOI)000679144000001 ()
Available from: 2021-09-24 Created: 2021-09-24 Last updated: 2022-02-25Bibliographically approved
Bertoli, G., Bohm, C., Carney, R. M. D., Clément, C., Gellerstedt, K., Hellman, S., . . . Wallängen, V. (2020). ATLAS data quality operations and performance for 2015-2018 data-taking. Journal of Instrumentation, 15(4), Article ID P04003.
Open this publication in new window or tab >>ATLAS data quality operations and performance for 2015-2018 data-taking
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2020 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 15, no 4, article id P04003Article in journal (Refereed) Published
Abstract [en]

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 root s = 13 TeV certified for physics analysis.

Keywords
Large detector systems for particle and astroparticle physics, Large detector-systems performance
National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-183172 (URN)10.1088/1748-0221/15/04/P04003 (DOI)000534740000003 ()
Available from: 2020-07-01 Created: 2020-07-01 Last updated: 2022-03-23Bibliographically approved
Backman, F., Barranco Navarro, L., Bohm, C., Carney, R. M. D., Clement, C., Hellman, S., . . . Wallängen, V. (2020). Combination of searches for Higgs boson pairs in pp collisions at root s=13 TeV with the ATLAS detector. Physics Letters B, 800, Article ID 135103.
Open this publication in new window or tab >>Combination of searches for Higgs boson pairs in pp collisions at root s=13 TeV with the ATLAS detector
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2020 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 800, article id 135103Article in journal (Refereed) Published
Abstract [en]

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 root 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 b (b) over barb (b) over bar, b (b) over barW(+)W(-), b (b) over bar tau(+)tau(-), W+W-W+W-, b (b) over bar gamma gamma and W+W-gamma gamma 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 (kappa(lambda)) 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 < kappa(lambda) < 12.0 (-5.8 < kappa(lambda) < 12.0). In addition, limits are set on the production of narrow scalar resonances and spin-2 Kaluza-Klein Randall-Sundrum gravitons. Exclusion regions are also provided in the parameter space of the habemus Minimal Supersymmetric Standard Model and the Electroweak Singlet Model.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-178606 (URN)10.1016/j.physletb.2019.135103 (DOI)000503832500009 ()
Available from: 2020-03-13 Created: 2020-03-13 Last updated: 2022-03-23Bibliographically approved
Backman, F., Barranco Navarro, L., Bohm, C., Carney, R. M. D., Clement, C., Hellman, S., . . . Wallängen, V. (2020). Combined measurements of Higgs boson production and decay using up to 80 fb(-1) of proton-proton collision data at root S=13 TeV collected with the ATLAS experiment. Physical Review D: covering particles, fields, gravitation, and cosmology, 101(1), Article ID 012002.
Open this publication in new window or tab >>Combined measurements of Higgs boson production and decay using up to 80 fb(-1) of proton-proton collision data at root S=13 TeV collected with the ATLAS experiment
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2020 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 101, no 1, article id 012002Article in journal (Refereed) Published
Abstract [en]

Combined measurements of Higgs boson production cross sections and branching fractions arc presented. The combination is based on the analyses of the Higgs boson decay modes H -> gamma gamma, ZZ*, WW*, tau tau, b (b) over bar, mu mu, 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 root 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 mu = 1.11(-0.08)(+0.09). The combined measurement yields an observed (expected) significance for the vector-boson fusion production process of 6.5 sigma (5.3 sigma). 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 supersynunetric Standard Model. No significant deviations from Standard Model predictions are observed.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-178630 (URN)10.1103/PhysRevD.101.012002 (DOI)000505485600001 ()
Available from: 2020-03-13 Created: 2020-03-13 Last updated: 2022-03-23Bibliographically approved
Bertoli, G., Bessidskaia Bylund, O., Bohm, C., Carney, R. M. D., Clement, C., Gellerstedt, K., . . . Wallängen, V. (2020). Determination of jet calibration and energy resolution in proton-proton collisions at s=8 TeV using the ATLAS detector. European Physical Journal C, 80(12), Article ID 1104.
Open this publication in new window or tab >>Determination of jet calibration and energy resolution in proton-proton collisions at s=8 TeV using the ATLAS detector
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2020 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 80, no 12, article id 1104Article in journal (Refereed) Published
Abstract [en]

The jet energy scale, jet energy resolution, and their systematic uncertainties are measured for jets reconstructed with the ATLAS detector in 2012 using proton-proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of 20 fb-1. Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti-kt algorithm. A jet calibration scheme is applied in multiple steps, each addressing specific effects including mitigation of contributions from additional proton-proton collisions, loss of energy in dead material, calorimeter non-compensation, angular biases and other global jet effects. The final calibration step uses several in situ techniques and corrects for residual effects not captured by the initial calibration. These analyses measure both the jet energy scale and resolution by exploiting the transverse momentum balance in gamma + jet, Z + jet, dijet, and multijet events. A statistical combination of these measurements is performed. In the central detector region, the derived calibration has a precision better than 1% for jets with transverse momentum 150 GeV<pT< 1500 GeV, and the relative energy resolution is (8.4 +/- 0.6)% for pT=100 GeV and (23 +/- 2)% for pT=20 GeV. The calibration scheme for jets with radius parameter R=1.0, for which jets receive a dedicated calibration of the jet mass, is also discussed.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-190699 (URN)10.1140/epjc/s10052-020-08477-8 (DOI)000598026400006 ()
Available from: 2021-03-03 Created: 2021-03-03 Last updated: 2022-02-25Bibliographically approved
Backman, F., Barranco Navarro, L., Bohm, C., Carney, R. M. D., Clement, C., Hellman, S., . . . Wallängen, V. (2020). Evidence for electroweak production of two jets in association with a Z gamma pair in pp collisions at root S=13 TeV with the ATLAS detector. Physics Letters B, 803, Article ID 135341.
Open this publication in new window or tab >>Evidence for electroweak production of two jets in association with a Z gamma pair in pp collisions at root S=13 TeV with the ATLAS detector
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2020 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 803, article id 135341Article in journal (Refereed) Published
Abstract [en]

Evidence for electroweak production of two jets in association with a Z gamma pair in root s = 13 TeV proton-proton collisions at the Large Hadron Collider is presented. The analysis uses data collected by the ATLAS detector in 2015 and 2016 that corresponds to an integrated luminosity of 36.1 fb(-1). Events that contain a Z boson candidate decaying leptonically into either e(+)e(-) or mu(+)mu(-), a photon, and two jets are selected. The electroweak component is measured with observed and expected significances of 4.1 standard deviations. The fiducial cross-section for electroweak production is measured to be sigma(Z gamma jj-Ew) = 7.8 +/- 2.0 fb, in good agreement with the Standard Model prediction.

National Category
Physical Sciences
Identifiers
urn:nbn:se:su:diva-181320 (URN)10.1016/j.physletb.2020.135341 (DOI)000521730300023 ()
Available from: 2020-05-24 Created: 2020-05-24 Last updated: 2022-03-23Bibliographically approved
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