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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, A., Bailey, A. J., Bouchhar, N., et al. (2024). Measurement and interpretation of same-sign W boson pair production in association with two jets in pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 04(4), 026–61pp.
Abstract: This paper presents the measurement of fiducial and differential cross sections for both the inclusive and electroweak production of a same-sign W-boson pair in association with two jets ( W-+/- W(+/-)jj) using 139 fb(-1) of proton-proton collision data recorded at a centre-of-mass energy of root s = 13TeV by the ATLAS detector at the Large Hadron Collider. The analysis is performed by selecting two same-charge leptons, electron or muon, and at least two jets with large invariant mass and a large rapidity difference. The measured fiducial cross sections for electroweak and inclusive W-+/- W-+/- jj production are 2.92 +/- 0.22 (stat.) +/- 0.19 (syst.) fb and 3.38 +/- 0.22 (stat.)+/- 0.19 (syst.) fb, respectively, in agreement with Standard Model predictions. The measurements are used to constrain anomalous quartic gauge couplings by extracting 95% confidence level intervals on dimension-8 operators. A search for doubly charged Higgs bosons H-+/-+/- that are produced in vector-boson fusion processes and decay into a same-sign W boson pair is performed. The largest deviation from the Standard Model occurs for an H-+/-+/- mass near 450 GeV, with a global significance of 2.5 standard deviations.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2024). Differential cross-sections for events with missing transverse momentum and jets measured with the ATLAS detector in 13 TeV proton-proton collisions. J. High Energy Phys., 08(8), 223–62pp.
Abstract: Measurements of inclusive, differential cross-sections for the production of events with missing transverse momentum in association with jets in proton-proton collisions at root s = 13 TeV are presented. The measurements are made with the ATLAS detector using an integrated luminosity of 140 fb(-1) and include measurements of dijet distributions in a region in which vector-boson fusion processes are enhanced. They are unfolded to correct for detector resolution and efficiency within the fiducial acceptance, and are designed to allow robust comparisons with a wide range of theoretical predictions. A measurement of differential cross sections for the Z -> nu nu process is made. The measurements are generally well-described by Standard Model predictions except for the dijet invariant mass distribution. Auxiliary measurements of the hadronic system recoiling against isolated leptons, and photons, are also made in the same phase space. Ratios between the measured distributions are then derived, to take advantage of cancellations in modelling effects and some of the major systematic uncertainties. These measurements are sensitive to new phenomena, and provide a mechanism to easily set constraints on phenomenological models. To illustrate the robustness of the approach, these ratios are compared with two common Dark Matter models, where the constraints derived from the measurement are comparable to those set by dedicated detector-level searches.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Aparisi Pozo, J. A., Bailey, A. J., Bouchhar, N., et al. (2023). Evidence of pair production of longitudinally polarised vector bosons and study of CP properties in ZZ → 4l events with the ATLAS detector at √s=13 TeV. J. High Energy Phys., 12(12), 107–48pp.
Abstract: A study of the polarisation and CP properties in ZZ production is presented. The used data set corresponds to an integrated luminosity of 140 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13TeV recorded by the ATLAS detector at the Large Hadron Collider. The ZZ candidate events are reconstructed using two same-flavour opposite-charge electron or muon pairs. The production of two longitudinally polarised Z bosons is measured with a significance of 4.3 standard deviations, and its cross-section is measured in a fiducial phase space to be 2.45 +/- 0.60 fb, consistent with the next-to-leadingorder Standard Model prediction. The inclusive differential cross-section as a function of a CP-sensitive angular observable is also measured. The results are used to constrain anomalous CP-odd neutral triple gauge couplings.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2025). Measurements and interpretations of W±Z production cross-sections in pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 11(11), 006–68pp.
Abstract: Measurements of integrated and differential cross-sections for W(+/-)Z production in proton-proton collisions are presented. The data collected by the ATLAS detector at the Large Hadron Collider from 2015 to 2018 at a centre-of-mass energy of root s = 13TeV are used, corresponding to an integrated luminosity of 140 fb(-1). The W(+/-)Z candidate events are reconstructed using leptonic decay modes of the gauge bosons into electrons or muons. The integrated cross-section per lepton flavour for the production of W(+/-)Z is measured in the detector fiducial region with a relative precision of 4%. The measured value is compared with the Standard Model prediction at a precision of up to next-to-next-to-leading-order in QCD and next-to-leading-order in electroweak. Cross-sections for W(+)Z and W(-)Z production and their ratio are presented. The W(+/-)Z production is also measured differentially as functions of various kinematic variables, including new observables sensitive to CP-violation effects. All measurements are compared with state-of-the-art Standard Model predictions from fixed-order calculations or Monte Carlo generators based on next-to-leading-order matrix elements interfaced with parton showers. An effective field theory interpretation of the measurements is performed, considering both CP-conserving and CP-violating dimension-6 operators modifying the W(+/-)Z production. In the absence of observed deviations from the Standard Model, limits on CP-conserving Wilson coefficients are extracted using the transverse mass of the W(+/-)Z system. For CP-violating coefficients a machine learning approach is used to construct an observable with enhanced sensitivity to CP-violation effects.
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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2024). Measurements of electroweak W±Z boson pair production in association with two jets in pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 06(6), 192–55pp.
Abstract: Measurements of integrated and differential cross-sections for electroweak WZ production in association with two jets (W(+/-)Zjj) in proton-proton collisions are presented. The data collected by the ATLAS detector at the Large Hadron Collider from 2015 to 2018 at a centre-of-mass energy of root s = 13 TeV are used, corresponding to an integrated luminosity of 140 fb(-1). The W(+/-)Zjj candidate events are reconstructed using leptonic decay modes of the gauge bosons. Events containing three identified leptons, either electrons or muons, and two jets are selected. Processes involving pure electroweak W(+/-)Zjj production at Born level are separated from W(+/-)Zjj production involving a strong coupling. The measured integrated fiducial cross-section of electroweak W(+/-)Zjj production per lepton flavour is sigma(WZjj-EW -> l 'nu lljj) = 0.368 +/- 0.037 (stat.) +/- 0.059 (syst.) +/- 0.003 (lumi.) fb, where l and l ' are either an electron or a muon. Respective cross-sections of electroweak and strong W(+/-)Zjj production are measured separately for events with exactly two jets or with more than two jets, and in three bins of the invariant mass of the two jets. The inclusive W(+/-)Zjj production cross-section, without separating electroweak and strong production, is also measured to be sigma(WZjj -> l 'nu lljj) = 1.462 +/- 0.063 (stat.) +/- 0.118 (syst.) +/- 0.012 (lumi.) fb, per lepton flavour. The inclusive W(+/-)Zjj production cross-section is measured differentially for several kinematic observables. Finally, the measurements are used to constrain anomalous quartic gauge couplings by extracting 95% confidence level intervals on dimension-8 operators.
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