Evidence for tt̄tt̄ production in the multilepton final state in proton–proton collisions at √s = 13 TeV with the ATLAS detector at the LHC
Evidence for tt̄tt̄ production in the multilepton final state in proton–proton collisions at √s = 13 TeV with the ATLAS detector at the LHC
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DissertationDate of Exam
17.12.2024Date of Publication
20.01.2025Advisor
Cristinziani, MarkusCo-Referee
Dingfelder, JochenMetadata
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Abstract
The first evidence for simultaneous production of four top quarks is presented. The measurement is conducted by selecting events having two same-charge leptons or at least three leptons and by analysing 139 fb-1 of proton–proton collision data at a centre-of-mass energy of √s = 13 TeV provided by the LHC and collected by the ATLAS detector. In addition to simulated samples, data-driven methods are utilised for the estimation of background contributions. A multivariate discriminant is developed to separate tt̄tt̄ signal from the background processes using the Boosted Decision Tree (BDT) method. The production cross-section is extracted using a binned profile-likelihood fit to all control regions and the BDT distribution in the signal region simultaneously and is measured to be
δtt̄tt̄ = 24 ± 5(stat.)+5− 4(syst.) fb = 24+7− 6 fb,
corresponding to an observed (expected) statistical significance of 4.3 (2.9) standard deviations from the background-only hypothesis. The analysis model is used to set limits on the top-quark Yukawa coupling parameter γt . A pure CP-even (CP-odd) coupling is excluded for |γt| > 2.2 (|γt| > 1.6) at the 95% confidence level. No deviations from the Standard Model of particle physics prediction has been found.
δtt̄tt̄ = 24 ± 5(stat.)+5− 4(syst.) fb = 24+7− 6 fb,
corresponding to an observed (expected) statistical significance of 4.3 (2.9) standard deviations from the background-only hypothesis. The analysis model is used to set limits on the top-quark Yukawa coupling parameter γt . A pure CP-even (CP-odd) coupling is excluded for |γt| > 2.2 (|γt| > 1.6) at the 95% confidence level. No deviations from the Standard Model of particle physics prediction has been found.
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530 PhysikÖncel, Ö. Oğul: Evidence for tt̄tt̄ production in the multilepton final state in proton–proton collisions at √s = 13 TeV with the ATLAS detector at the LHC. - Bonn, 2025. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-80526
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-80526
@phdthesis{handle:20.500.11811/12744,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-80526,
author = {{Ö. Oğul Öncel}},
title = {Evidence for tt̄tt̄ production in the multilepton final state in proton–proton collisions at √s = 13 TeV with the ATLAS detector at the LHC},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2025,
month = jan,
note = {The first evidence for simultaneous production of four top quarks is presented. The measurement is conducted by selecting events having two same-charge leptons or at least three leptons and by analysing 139 fb-1 of proton–proton collision data at a centre-of-mass energy of √s = 13 TeV provided by the LHC and collected by the ATLAS detector. In addition to simulated samples, data-driven methods are utilised for the estimation of background contributions. A multivariate discriminant is developed to separate tt̄tt̄ signal from the background processes using the Boosted Decision Tree (BDT) method. The production cross-section is extracted using a binned profile-likelihood fit to all control regions and the BDT distribution in the signal region simultaneously and is measured to be
δtt̄tt̄ = 24 ± 5(stat.)+5− 4(syst.) fb = 24+7− 6 fb,
corresponding to an observed (expected) statistical significance of 4.3 (2.9) standard deviations from the background-only hypothesis. The analysis model is used to set limits on the top-quark Yukawa coupling parameter γt . A pure CP-even (CP-odd) coupling is excluded for |γt| > 2.2 (|γt| > 1.6) at the 95% confidence level. No deviations from the Standard Model of particle physics prediction has been found.},
url = {https://hdl.handle.net/20.500.11811/12744}
}
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-80526,
author = {{Ö. Oğul Öncel}},
title = {Evidence for tt̄tt̄ production in the multilepton final state in proton–proton collisions at √s = 13 TeV with the ATLAS detector at the LHC},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2025,
month = jan,
note = {The first evidence for simultaneous production of four top quarks is presented. The measurement is conducted by selecting events having two same-charge leptons or at least three leptons and by analysing 139 fb-1 of proton–proton collision data at a centre-of-mass energy of √s = 13 TeV provided by the LHC and collected by the ATLAS detector. In addition to simulated samples, data-driven methods are utilised for the estimation of background contributions. A multivariate discriminant is developed to separate tt̄tt̄ signal from the background processes using the Boosted Decision Tree (BDT) method. The production cross-section is extracted using a binned profile-likelihood fit to all control regions and the BDT distribution in the signal region simultaneously and is measured to be
δtt̄tt̄ = 24 ± 5(stat.)+5− 4(syst.) fb = 24+7− 6 fb,
corresponding to an observed (expected) statistical significance of 4.3 (2.9) standard deviations from the background-only hypothesis. The analysis model is used to set limits on the top-quark Yukawa coupling parameter γt . A pure CP-even (CP-odd) coupling is excluded for |γt| > 2.2 (|γt| > 1.6) at the 95% confidence level. No deviations from the Standard Model of particle physics prediction has been found.},
url = {https://hdl.handle.net/20.500.11811/12744}
}
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