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Abstract:

Wilson coefficients in dimension-six effective field theory are constrained in a combined fit to several ATLAS measurements. These inputs probe Higgs-boson processes across multiple production and decay modes, di-Higgs signatures in the bb¯γγ$$ b\overline{b}\gamma \gamma $$ and bb¯ττ$$ b\overline{b}\tau \tau $$ final states, WW and WZ diboson signatures, electroweak Zjj final states, high-mass Drell–Yan interactions, and tt¯$$ t\overline{t} $$ events in both resolved and boosted topologies. Precision electroweak observables from LEP, SLD, and ATLAS are also included. A total of 48 parameters, including individual Wilson coefficients in the Warsaw basis and linear combinations of Wilson coefficients, are constrained simultaneously. Constraints on two-Higgs-doublet models and heavy-vector-boson models are also obtained by matching a relevant sub-set of the results with their parameters. This combined fit provides the most comprehensive effective field theory interpretation of experimental data by the ATLAS Collaboration to date. No significant deviations from the Standard Model are observed.

Abstract:

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 s=13$$ \sqrt{s}=13 $$ 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.