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Observation of four-top-quark production in the multilepton final state with the ATLAS detector
Acknowledgements: We thank CERN for the very successful operation of the LHC, as well as the support staff from our institutions without whom ATLAS could not be operated efficiently. We acknowledge the support of ANPCyT, Argentina; YerPhI, Armenia; ARC, Australia; BMWFW and FWF, Austria; ANAS, Azerbaijan; CNPq and FAPESP, Brazil; NSERC, NRC and CFI, Canada; CERN; ANID, Chile; CAS, MOST and NSFC, China; Minciencias, Colombia; MEYS CR, Czech Republic; DNRF and DNSRC, Denmark; IN2P3-CNRS and CEA-DRF/IRFU, France; SRNSFG, Georgia; BMBF, HGF and MPG, Germany; GSRI, Greece; RGC and Hong Kong SAR, China; ISF and Benoziyo Center, Israel; INFN, Italy; MEXT and JSPS, Japan; CNRST, Morocco; NWO, Netherlands; RCN, Norway; MEiN, Poland; FCT, Portugal; MNE/IFA, Romania; MESTD, Serbia; MSSR, Slovakia; ARRS and MIZŠ, Slovenia; DSI/NRF, South Africa; MICINN, Spain; SRC and Wallenberg Foundation, Sweden; SERI, SNSF and Cantons of Bern and Geneva, Switzerland; MOST, Taiwan; TENMAK, Türkiye; STFC, United Kingdom; DOE and NSF, United States of America. In addition, individual groups and members have received support from BCKDF, CANARIE, Compute Canada and CRC, Canada; PRIMUS 21/SCI/017 and UNCE SCI/013, Czech Republic; COST, ERC, ERDF, Horizon 2020 and Marie Skłodowska-Curie Actions, European Union; Investissements d’Avenir Labex, Investissements d’Avenir Idex and ANR, France; DFG and AvH Foundation, Germany; Herakleitos, Thales and Aristeia programmes co-financed by EU-ESF and the Greek NSRF, Greece; BSF-NSF and MINERVA, Israel; Norwegian Financial Mechanism 2014-2021, Norway; NCN and NAWA, Poland; La Caixa Banking Foundation, CERCA Programme Generalitat de Catalunya and PROMETEO and GenT Programmes Generalitat Valenciana, Spain; Göran Gustafssons Stiftelse, Sweden; The Royal Society and Leverhulme Trust, United Kingdom. The crucial computing support from all WLCG partners is acknowledged gratefully, in particular from CERN, the ATLAS Tier-1 facilities at TRIUMF (Canada), NDGF (Denmark, Norway, Sweden), CC-IN2P3 (France), KIT/GridKA (Germany), INFN-CNAF (Italy), NL-T1 (Netherlands), PIC (Spain), ASGC (Taiwan), RAL (UK) and BNL (USA), the Tier-2 facilities worldwide and large non-WLCG resource providers. Major contributors of computing resources are listed in Ref. [118].AbstractThis paper presents the observation of four-top-quark (
t
t
¯
t
t
¯
) production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity of 140
fb
-
1
at a centre-of-mass energy of 13 TeV collected using the ATLAS detector. Events containing two leptons with the same electric charge or at least three leptons (electrons or muons) are selected. Event kinematics are used to separate signal from background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The observed (expected) significance of the measured
t
t
¯
t
t
¯
signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The
t
t
¯
t
t
¯
production cross section is measured to be
22
.
5
-
5.5
+
6.6
fb, consistent with the SM prediction of
12.0
±
2.4
fb within 1.8 standard deviations. Data are also used to set limits on the three-top-quark production cross section, being an irreducible background not measured previously, and to constrain the top-Higgs Yukawa coupling and effective field theory operator coefficients that affect
t
t
¯
t
t
¯
production.</jats:p
Erratum to: Observation of four-top-quark production in the multilepton final state with the ATLAS detector
Corrections to two figures, one table and the corresponding numbers in the text are noted for the paper. Systematic uncertainties arising from the comparison of the nominal tt¯tt¯ simulation with alternative samples generated with Sherpa and with MadGraph5_aMC@NLO+Herwig7 were not applied when deriving limits on the top-quark Yukawa coupling, Higgs oblique parameter and EFT operators. This affects Figs. 8 and 9, and Table 8. (Figure presented.) (Figure presented.) (Table presented.) Two-dimensional negative log-likelihood contours for |κtcos(α)| versus |κtsin(α)| at 68% and 95%, where κt is the top-Higgs Yukawa coupling strength parameter and α is the mixing angle between the CP-even and CP-odd components. The gradient-shaded area represents the observed likelihood value as a function of κt and α. Both the tt¯tt¯ signal and tt¯H background yields in each fitted bin are parameterised as a function of κt and α. The blue cross shows the SM expectation, while the black cross shows the best fit value The negative log-likelihood values as a function of the Higgs oblique parameter H^. The solid line represents the observed likelihood while the dashed line corresponds to the expected one. The dashed region shows the non-unitary regime Expected and observed 95% CL intervals on EFT coupling parameters assuming one EFT parameter variation in the fit Operators Expected Ci/Λ2 [TeV -2] Observed Ci/Λ2 [TeV -2] OQQ1 [-2.5,3.2] [-4.0,4.5] OQt1 [-2.6,2.1] [-3.8,3.4] Ott1 [-1.2,1.4] [-1.9,2.1] OQt8 [-4.3,5.1] [-6.9,7.6] The changes in the text are noted for Sects. 9.1, 9.2 and 10. In Sect. 9.1, for the case when the tt¯tt¯ and tt¯H yields in each bin of the GNN distribution are parameterised as a function of κt and α and fixing the top-quark Yukawa coupling to be CP-even only, the observed limit is |κt|<1.9 instead of |κt|<1.8. If the tt¯H background yields are not parametrised, whilst the normalisation of the tt¯H background is treated as a free parameter of the fit, the observed (expected) limit is |κt|<2.3 (1.9) instead of |κt|<2.2 (1.8). In Sect. 9.2, the upper limits on the absolute values of the coefficients (|Ci/Λ2|) of OQQ1, OQt1, Ott1 and OQt8 assuming only the linear terms are 6.6, 4.0, 2.8 and 10.8 TeV -2, respectively, at 95% CL instead of 5.3, 3.3, 2.4 and 8.8 TeV -2. In Sect. 9.2, the observed (expected) upper limit on the H^ parameter is 0.23 (0.11) at 95% CL instead of 0.20 (0.12). The published expected upper limit of 0.12 was a mistake in the text and should have been 0.1 corresponding to the likelihood scan in Fig. 9. The observed limit is weaker than the largest value of this parameter equal to 0.2 that preserves unitarity in the perturbative theory. In Sect. 10, assuming a pure CP-even coupling (α=0), the observed upper limit on |κt|=|yt/ytSM| at 95% CL is 1.9 instead of 1.8. Assuming one operator taking effect at a time, the observed constraints on the coefficients (Ci/Λ2) of OQQ1, OQt1, Ott1 and OQt8 are [-4.0,4.5], [-3.8,3.4], [-1.9,2.1] and [-6.9,7.6] TeV -2, respectively. An observed upper limit at 95% CL of 0.23 is obtained for the Higgs oblique parameter that is weaker than the largest value that preserves unitarity in the perturbative theory. In Sect. 9.1, for the case when the tt¯tt¯ and tt¯H yields in each bin of the GNN distribution are parameterised as a function of κt and α and fixing the top-quark Yukawa coupling to be CP-even only, the observed limit is |κt|<1.9 instead of |κt|<1.8. If the tt¯H background yields are not parametrised, whilst the normalisation of the tt¯H background is treated as a free parameter of the fit, the observed (expected) limit is |κt|<2.3 (1.9) instead of |κt|<2.2 (1.8). In Sect. 9.2, the upper limits on the absolute values of the coefficients (|Ci/Λ2|) of OQQ1, OQt1, Ott1 and OQt8 assuming only the linear terms are 6.6, 4.0, 2.8 and 10.8 TeV -2, respectively, at 95% CL instead of 5.3, 3.3, 2.4 and 8.8 TeV -2. In Sect. 9.2, the observed (expected) upper limit on the H^ parameter is 0.23 (0.11) at 95% CL instead of 0.20 (0.12). The published expected upper limit of 0.12 was a mistake in the text and should have been 0.1 corresponding to the likelihood scan in Fig. 9. The observed limit is weaker than the largest value of this parameter equal to 0.2 that preserves unitarity in the perturbative theory. In Sect. 10, assuming a pure CP-even coupling (α=0), the observed upper limit on |κt|=|yt/ytSM| at 95% CL is 1.9 instead of 1.8. Assuming one operator taking effect at a time, the observed constraints on the coefficients (Ci/Λ2) of OQQ1, OQt1, Ott1 and OQt8 are [-4.0,4.5], [-3.8,3.4], [-1.9,2.1] and [-6.9,7.6] TeV -2, respectively. An observed upper limit at 95% CL of 0.23 is obtained for the Higgs oblique parameter that is weaker than the largest value that preserves unitarity in the perturbative theory