I. S. Bordulev

A bstract: A search for heavy spin-1 and spin-2 resonances decaying into a top-antitop-quark pair has been performed with 140 fb ^{− 1} of proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider at a centre-of-mass energy of $$ \sqrt{s}=13 $$ s = 13 TeV. Final states with either exactly one electron or muon, or exactly two leptons ( ee , μμ or eμ ), large missing transverse momentum, and two jets, at least one of which must be identified as likely containing a b -hadron decay, are considered. The search targets resonances with both narrow and broad widths relative to the detector resolution, and with masses in the range of 0.4–5.0 TeV. No significant deviation from the Standard Model prediction is observed. Exclusion limits are set on the production cross-section times branching ratio for hypothetical Z′ bosons, Kaluza-Klein gravitons, and Kaluza-Klein gluons that decay into top-quark pairs.

A measurement of correction factors for the hadronic jet energy scale and resolution in the ATLAS detector is presented. These correction factors account for differences between simulated and observed data. They are obtained by analysing a selection of top quark events collected in proton–proton collisions by ATLAS between the years 2015 and 2018 at a centre-of-mass energy $$\sqrt{s} = 13$$ s = 13 $$\text {TeV}$$ TeV as well as in 2022 and 2023 at $$\sqrt{s} = 13.6$$ s = 13.6 $$\text {TeV}$$ TeV . The impact of different jet energy scale or resolution corrections on the reconstructed mass of the hadronically decaying W boson from top-quark decays in simulation is quantified. The correction factors are extracted from a fit to the parameterised reconstructed W -boson mass distribution to data. The energy scale and resolution corrections are measured as a function of the jet transverse momentum between 20 and 200 $$\text {GeV}$$ GeV and absolute pseudorapidity less than 0.8. The uncertainties in the energy scale range from about 0.93% to about 1.7% for jets between 35 and 200 $$\text {GeV}$$ GeV , while for the energy resolution the uncertainties range from about 14 to 28%. The method presented will be used in conjunction with other techniques to further improve ATLAS jet energy scale and resolution precision.

A bstract: A search is conducted in proton–proton collisions at the Large Hadron Collider for photon-induced production pp → pp + γγ, ( γγ → VX ) of a visible particle V decaying into a pair of same-flavour charged leptons ( e ⁺ e ⁻ or μ ⁺ μ ⁻ ) and an undetected invisible component X . Measurements of the outgoing proton energies by the ATLAS forward proton spectrometer allow the full photon–photon four-momentum to be reconstructed. By subtracting the visible four-momentum of the central system measured with the ATLAS detector, the “missing mass” of any event components not detected in the central region can be reconstructed, enabling the reconstruction of X without knowing its properties, thus allowing the search to be model-independent. A search for a narrow resonance is performed in the missing-mass spectrum between 100 GeV and 900 GeV. The analysis uses data collected in 2017 from proton–proton collisions at a centre-of-mass energy of $$ \sqrt{s}=13 $$ s = 13 TeV, corresponding to an integrated luminosity of 14.7 fb ^{− 1} . No significant excess over the Standard Model expectation is observed and upper limits at 95% confidence level are set on the fiducial cross sections for three different signal models in the range between 128 and 2.5 fb. Additionally, model-independent limits are set on the visible cross section of BSM processes, for two sets of selection criteria. Both individual lepton flavour decay channels of the visible boson and a combination of the two channels are considered.

A search is presented for emerging jets using $$140~\textrm{fb}^{-1}$$ 140 fb - 1 of proton–proton collision data at $$\sqrt{s} = 13~\textrm{TeV}$$ s = 13 TeV , collected by the ATLAS experiment between 2015 and 2018. The search looks for the existence of a dark sector with symmetries similar to those in quantum chromodynamics. This dark sector is populated with dark quarks, which undergo showering similar to quarks in the Standard Model, leading to a high multiplicity of long-lived dark hadrons within a dark jet. These dark hadrons subsequently decay to Standard Model particles via a new heavy scalar mediating particle $$\phi $$ ϕ . This results in jets which contain multiple displaced vertices, known as emerging jets. This analysis targets four-jet topologies, with two emerging jets and two Standard Model jets, resulting from the decay of pair-produced scalar mediators. No significant excess above the Standard Model background is observed. For dark pion proper decay lengths of $$20~\textrm{mm}$$ 20 mm , mediator masses are excluded between 1 and $$2~\textrm{TeV}$$ 2 TeV assuming a dark pion mass of $$20~\textrm{GeV}$$ 20 GeV .

A bstract: Events with t -channel single top quarks are used to probe effective field theory operators in $$ \sqrt{s}=13 $$ s = 13 TeV proton–proton collision data corresponding to 140 fb ^{− 1} recorded by the ATLAS detector at the Large Hadron Collider. To extract a maximum amount of information from these events, the joint fourfold probability distribution for four kinematic angles is simultaneously analysed. A method leveraging Fourier techniques to handle the challenges arising from this approach is employed. The relevant effective field theory operators are those sensitive to top-quark decay and t -channel production vertices. Their Wilson coefficients are tightly constrained, with results compatible with Standard Model predictions.

A bstract: This paper presents differential cross-section measurements of events containing a charged lepton, missing transverse momentum, two b -jets, and two light jets, consistent with the $$ {W}^{+}{W}^{-}b\overline{b} $$ W + W − b b ¯ final state. The analysis is based on 140 fb ^{− 1} of proton-proton collision data at $$ \sqrt{s}=13 $$ s = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider (2015–2018). Differential cross-sections are unfolded at particle level for a range of kinematic observables and in three kinematic regions. Both regions and observables are optimised for sensitivity to the interference between $$ {W}^{+}{W}^{-}b\overline{b} $$ W + W − b b ¯ produced with singly and doubly resonant top quarks. Results are compared with various theoretical predictions and deviations are observed in regions sensitive to the interference between singly and doubly resonant top-quark production. The unfolded results provide new information about the modelling of interference and off-shell effects of the $$ {W}^{+}{W}^{-}b\overline{b} $$ W + W − b b ¯ final state, improving the understanding of top-quark production mechanisms and providing new inputs for future Monte Carlo generator development.