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One doublet of complex scalar fields is the minimal content of the Higgs sector in order to achieve spontaneous electroweak symmetry breaking and, in turn, to generate the masses of fundamental particles in the Standard Model. However, several theories beyond the Standard Model predict a nonminimal Higgs sector and introduce additional singlets, doublets or even higher-order weak isospin representations, thereby yielding additional Higgs bosons. With its high proton–proton collision energy (13 TeV during Run-2), the Large Hadron Collider opens a new window towards the exploration of extended Higgs sectors. This review article summarises the current state-of-the-art experimental results recently obtained in searches for new neutral and charged Higgs bosons with a partial or full Run-2 dataset.

With respect to the original review article [1], the corrected couplings of the Higgs doublets Φ1 and Φ2 in the 2HDM type-I, type-II, lepton-specific and flipped scenarios are shown in Table 1 [...]

A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of root s = 13 TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb(-1). The results are interpreted in the context of various R-parity-conserving models where squarks and gluinos are produced in pairs or in association and a neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.30 TeV for a simplified model containing only a gluino and the lightest neutralino, assuming the latter is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.85 TeV are excluded if the lightest neutralino is massless. These limits extend substantially beyond the region of supersymmetric parameter space excluded previously by similar searches with the ATLAS detector.

This paper describes a measurement of light-by-light scattering based on Pb+Pb collision data recorded by the ATLAS experiment during Run 2 of the LHC. The study uses 2.2 nb(-1) of integrated luminosity collected in 2015 and 2018 at root sNN = 5.02TeV. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy E-T(gamma) > 2.5 GeV, pseudorapidity vertical bar eta(gamma)vertical bar < 2.37, diphoton invariant mass m(gamma gamma) > 5 GeV, and with small diphoton transverse momentum and diphoton acoplanarity. The integrated and differential fiducial cross sections are measured and compared with theoretical predictions. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles. This result provides the most stringent limits to date on axion-like particle production for masses in the range 6-100 GeV. Cross sections above 2 to 70 nb are excluded at the 95% CL in that mass interval.

In several theories beyond the Standard Model, the Higgs sector consists of more than one complex scalar doublet. For instance, supersymmetric models such as the MSSM have five physical Higgs states: two charged and three neutral. In this paper, a review of the searches for new neutral and charged Higgs bosons at the Large Hadron Collider, with the ATLAS experiment, is presented.

Cross-sections for the production of a Z boson in association with two photons are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data used correspond to an integrated luminosity of 139 fb(-1) recorded by the ATLAS experiment during Run 2 of the LHC. The measurements use the electron and muon decay channels of the Z boson, and a fiducial phase-space region where the photons are not radiated from the leptons. The integrated Z(-> ll)gamma gamma cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the Z gamma gamma system. The data are compared with predictions from MC event generators which are accurate to up to next-to-leading order in QCD. The cross-section measurements are used to set limits on the coupling strengths of dimension-8 operators in the framework of an effective field theory.

This paper presents measurements of top-antitop quark pair (t¯t) production inassociation with additional b-jets. The analysis utilises 140 fb −1 of proton–proton collisiondata collected with the ATLAS detector at the Large Hadron Collider at a centre-of-massenergy of 13 TeV. Fiducial cross-sections are extracted in a final state featuring one electronand one muon, with at least three or four b-jets . Results are presented at the particle level forboth integrated cross-sections and normalised differential cross-sections, as functions of globalevent properties, jet kinematics, and b-jet pair properties. Observable quantities characterisingb-jets originating from the top quark decay and additional b-jets are also measured at theparticle level, after correcting for detector effects. The measured integrated fiducial cross-sections are consistent with t¯tb¯b predictions from various next-to-leading-order matrix elementcalculations matched to a parton shower within the uncertainties of the predictions. State-of-the-art theoretical predictions are compared with the differential measurements; none ofthem simultaneously describes all observables. Differences between any two predictions aresmaller than the measurement uncertainties for most observables.

A measurement of the top-quark pole mass m t pole is presented in tt <over bar> events with an additional jet, tt <over bar>+ 1-jet, produced in pp collisions at √s = 13TeV. The data sample, recorded with the ATLAS experiment during Run 2 of the LHC, corresponds to an integrated luminosity of 140 fb -1 . Events with one electron and one muon of opposite electric charge in the final state are selected to measure the tt <over bar>+ 1-jet differential cross-section as a function of the inverse of the invariant mass of the tt <over bar> + 1-jet system. Iterative Bayesian Unfolding is used to correct the data to enable comparison with fixed-order calculations at next-to-leading-order accuracy in the strong coupling. The process pp → tt <over bar> j (2 → 3), where top quarks are taken as stable particles, and the process pp → bb <over bar>l + νl - ν<over bar> j (2 → 7), which includes top-quark decays to the dilepton final state and off-shell effects, are considered. The top-quark mass is extracted using χ 2 fit of the unfolded normalized differential cross-section distribution. The results obtained with the 2 → 3 and 2 → 7 calculations are compatible within theoretical uncertainties, providing an important consistency check. The more precise determination is obtained for the 2 → 3 measurement: m t pole = 170.7 ± 0.3 (stat.) ± 1.4 (syst.) ± 0.3 (scale) ±0.2 (PDF ⊕ α S ) GeV, which is in good agreement with other top-quark mass results.

Jets with different radius parameters R are an important tool for probing quantum chromodynamics processes at different angular scales. Jets with small R = 0.2 are instrumental in measurements of the substructure of large-R jets resulting from collimated hadronic decays of energetic W, Z, and Higgs bosons, top quarks, and of potential new resonances. This paper presents measurements of the energy scale, resolution, and associated uncertainties of jets with radius parameters R = 0.2 and 0.6, obtained using the ATLAS detector. The results are based on 37 fb(-1) of proton-proton collision data from the Large Hadron Collider at a centre-of-mass energy of root s = 13 TeV. A new in situ method for measuring jet energy scale differences between data and Monte Carlo simulations is presented. The systematic uncertainties in the jet energy scale for central jets (vertical bar eta vertical bar < 1.2) typically vary from 1% to about 5% as a function of vertical bar eta vertical bar at very low transverse momentum, p(T), of around 20 GeV for both R = 0.2 and 0.6 jets. The relative energy resolution ranges from (35 +/- 6)% at p(T) = 20 GeV to (6 +/- 0.5)% at p(T) = 300 GeV for central R = 0.2 jets, and is found to be slightly worse for R = 0.6 jets. Finally, the effect of close-by hadronic activity on the jet energy scale is investigated and is found to be well modelled by the ATLAS Monte Carlo simulations.

A measurement of the B-0 meson lifetime using B-0 -> J/psi K*(0) decays in data from 13 TeV proton-proton collisions with an integrated luminosity of 140 fb(-1) recorded by the ATLAS detector at the LHC is presented. The measured effective lifetime is tau = 1.5053 +/- 0.0012 (stat.) +/- 0.0035 (syst.) ps. The average decay width extracted from the effective lifetime, using parameters from external sources, is Gamma(d) = 0.6639 +/- 0.0005 (stat.) +/- 0.0016 (syst.) +/- 0.0038 (ext.) ps(-1), where the uncertainties are statistical, systematic and from external sources. The earlier ATLAS measurement of Gamma(s) in the B-s(0) -> J/psi phi decay was used to derive a value for the ratio of the average decay widths Gamma(d) and Gamma(s) for B-0 and B-s(0) mesons respectively, of Gamma(d)/Gamma(s) = 0.9905 +/- 0.0022 (stat.)+/- 0.0036 (syst.)+/- 0.0057 (ext.). Themeasured lifetime, average decay width and decay width ratio are in agreement with theoretical predictions and with measurements by other experiments. This measurement provides the most precise result of the effective lifetime of the B-0 meson to date.