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1. Search for new particles in final states with a boosted top quark and missing transverse momentum in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector

   https://doi.org/10.1007/JHEP05(2024)263  

   Aad, G; Abbott, B; Abeling, K; Abicht, N J; Abidi, S H; Aboulhorma, A; Abramowicz, H; Abreu, H; Abulaiti, Y; Acharya, B S; et al (May 2024, Journal of High Energy Physics)

   A<sc>bstract</sc> A search for events with one top quark and missing transverse momentum in the final state is presented. The fully hadronic decay of the top quark is explored by selecting events with a reconstructed boosted top-quark topology produced in association with large missing transverse momentum. The analysis uses 139 fb⁻¹of proton-proton collision data at a centre-of-mass energy of$$ \sqrt{s} $$ $\sqrt{s}$= 13 TeV recorded during 2015-2018 by the ATLAS detector at the Large Hadron Collider. The results are interpreted in the context of simplified models for Dark Matter particle production and the single production of a vector-likeTquark. Without significant excess relative to the Standard Model expectations, 95% confidence-level upper limits on the corresponding cross-sections are obtained. The production of Dark Matter particles in association with a single top quark is excluded for masses of a scalar (vector) mediator up to 4.3 (2.3) TeV, assumingm_χ= 1 GeV and the model couplingsλ_q= 0.6 andλ_χ= 0.4 (a= 0.5 andg_χ= 1). The production of a single vector-likeTquark is excluded for masses below 1.8 TeV assuming a coupling to the top quarkκ_T= 0.5 and a branching ratio forT → Ztof 25%. 

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2. Measurement of the top quark pole mass using $$ \textrm{t}\overline{\textrm{t}} $$+jet events in the dilepton final state in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV

   https://doi.org/10.1007/JHEP07(2023)077  

   Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Damanakis, K.; Dragicevic, M.; Escalante Del Valle, A.; Hussain, P. S.; Jeitler, M.; et al (July 2023, Journal of High Energy Physics)

   A<sc>bstract</sc> A measurement of the top quark pole mass$$ {m}_{\textrm{t}}^{\textrm{pole}} $$ $m_t^{\text{pole}}$in events where a top quark-antiquark pair ($$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$) is produced in association with at least one additional jet ($$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$+jet) is presented. This analysis is performed using proton-proton collision data at$$ \sqrt{s} $$ $\sqrt{s}$= 13 TeV collected by the CMS experiment at the CERN LHC, corresponding to a total integrated luminosity of 36.3 fb⁻¹. Events with two opposite-sign leptons in the final state (e⁺e⁻,μ⁺μ⁻, e^±μ^∓) are analyzed. The reconstruction of the main observable and the event classification are optimized using multivariate analysis techniques based on machine learning. The production cross section is measured as a function of the inverse of the invariant mass of the$$ \textrm{t}\overline{\textrm{t}} $$ $t\overline{t}$+jet system at the parton level using a maximum likelihood unfolding. Given a reference parton distribution function (PDF), the top quark pole mass is extracted using the theoretical predictions at next-to-leading order. For the ABMP16NLO PDF, this results in$$ {m}_{\textrm{t}}^{\textrm{pole}} $$ $m_t^{\text{pole}}$= 172.93±1.36 GeV. 

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3. Measurement of $$ t\overline{t} $$ production in association with additional b-jets in the eμ final state in proton–proton collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector

   https://doi.org/10.1007/JHEP01(2025)068  

   Aad, G; Aakvaag, E; Abbott, B; Abdelhameed, S; Abeling, K; Abicht, N J; Abidi, S H; Aboelela, M; Aboulhorma, A; Abramowicz, H; et al (January 2025, Journal of High Energy Physics)

   A<sc>bstract</sc> This paper presents measurements of top-antitop quark pair ($$ t\overline{t} $$ $t\overline{t}$) production in association with additionalb-jets. The analysis utilises 140 fb⁻¹of proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Fiducial cross-sections are extracted in a final state featuring one electron and one muon, with at least three or fourb-jets. Results are presented at the particle level for both integrated cross-sections and normalised differential cross-sections, as functions of global event properties, jet kinematics, andb-jet pair properties. Observable quantities characterisingb-jets originating from the top quark decay and additionalb-jets are also measured at the particle level, after correcting for detector effects. The measured integrated fiducial cross-sections are consistent with$$ t\overline{t}b\overline{b} $$ $t\overline{t}b\overline{b}$predictions from various next-to-leading-order matrix element calculations matched to a parton shower within the uncertainties of the predictions. State-of-the-art theoretical predictions are compared with the differential measurements; none of them simultaneously describes all observables. Differences between any two predictions are smaller than the measurement uncertainties for most observables. 

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4. Search for CP violation using $$ \textrm{t}\overline{\textrm{t}} $$ events in the lepton+jets channel in pp collisions at $$ \sqrt{s} $$ = 13 TeV

   https://doi.org/10.1007/JHEP06(2023)081  

   Tumasyan, A.; Adam, W.; Andrejkovic, J. W.; Bergauer, T.; Chatterjee, S.; Damanakis, K.; Dragicevic, M.; Escalante Del Valle, A.; Frühwirth, R.; Jeitler, M.; et al (June 2023, Journal of High Energy Physics)

   A<sc>bstract</sc> Results are presented on a search for CP violation in the production and decay of top quark-antiquark pairs in the lepton+jets channel. The search is based on data from proton-proton collisions at$$ \sqrt{s} $$ $\sqrt{s}$= 13 TeV, collected with the CMS detector, corresponding to an integrated luminosity of 138 fb⁻¹. Possible CP violation effects are evaluated by measuring asymmetries in observables constructed from linearly independent four-momentum vectors of the final-state particles. The dimensionless chromoelectric dipole moment of the top quark obtained from the observed asymmetries is measured to be 0.04 ± 0.10 (stat) ± 0.07(syst), and the asymmetries exhibit no evidence for CP-violating effects, consistent with expectations from the standard model. 

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5. Search for vector-boson resonances decaying into a top quark and a bottom quark using pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector

   https://doi.org/10.1007/JHEP12(2023)073  

   Aad, G; Abbott, B; Abeling, K; Abicht, N J; Abidi, S H; Aboulhorma, A; Abramowicz, H; Abreu, H; Abulaiti, Y; Abusleme_Hoffman, A C; et al (December 2023, Journal of High Energy Physics)

   A<sc>bstract</sc> A search for a new massive charged gauge boson,W′, is performed with the ATLAS detector at the LHC. The dataset used in this analysis was collected from proton-proton collisions at a centre-of-mass energy of$$ \sqrt{s} $$ $\sqrt{s}$= 13 TeV, and corresponds to an integrated luminosity of 139 fb⁻¹. The reconstructedtbinvariant mass is used to search for aW′ boson decaying into a top quark and a bottom quark. The result is interpreted in terms of aW′ boson with purely right-handed or left-handed chirality in a mass range of 0.5–6 TeV. Different values for the coupling of theW′ boson to the top and bottom quarks are considered, taking into account interference with single-top-quark production in thes-channel. No significant deviation from the background prediction is observed. The results are expressed as upper limits on theW′ →tbproduction cross-section times branching ratio as a function of theW′-boson mass and in the plane of the coupling vs theW′-boson mass. 

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