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Measurements of the ZZ and WW final states in the mass range above the 2 m Z and 2 m W thresholds provide a unique opportunity to measure the off-shell coupling strength of the Higgs boson. This paper presents constraints on the off-shell Higgs boson event yields normalised to the Standard Model prediction (signal strength) in the Z Z → 4 ℓ , Z Z → 2 ℓ 2 ν and W W → e ν μ ν final states. The result is based on pp collision data collected by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 20.3 fb - 1 at a collision energy of s = 8  TeV. Using the C L s method, the observed 95  % confidence level (CL) upper limit on the off-shell signal strength is in the range 5.1–8.6, with an expected range of 6.7–11.0. In each case the range is determined by varying the unknown g g → Z Z and g g → W W background K-factor from higher-order quantum chromodynamics corrections between half and twice the value of the known signal K-factor. Assuming the relevant Higgs boson couplings are independent of the energy scale of the Higgs boson production, a combination with the on-shell measurements yields an observed (expected) 95  % CL upper limit on Γ H / Γ H SM in the range 4.5–7.5 (6.5–11.2) using the same variations of the background K-factor. Assuming that the unknown g g → V V background K-factor is equal to the signal K-factor, this translates into an observed (expected) 95  % CL upper limit on the Higgs boson total width of 22.7 (33.0) MeV.

The ratio of the production cross sections for W and Z bosons in association with jets has been measured in proton–proton collisions at s = 7 TeV with the ATLAS experiment at the Large Hadron Collider. The measurement is based on the entire 2011 dataset, corresponding to an integrated luminosity of 4.6 fb - 1 . Inclusive and differential cross-section ratios for massive vector bosons decaying to electrons and muons are measured in association with jets with transverse momentum p T > 30 GeV and jet rapidity | y | < 4.4 . The measurements are compared to next-to-leading-order perturbative QCD calculations and to predictions from different Monte Carlo generators implementing leading-order matrix elements supplemented by parton showers.

A search for heavy resonances, decaying into the standard model vector bosons and the standard model Higgs boson, is presented. The final states considered contain a b quark-antiquark pair from the decay of the Higgs boson, along with electrons and muons and missing transverse momentum, due to undetected neutrinos, from the decay of the vector bosons. The mass spectra are used to search for a localized excess consistent with a resonant particle. The data sample corresponds to an integrated luminosity of 35.9 fb$^{−1}$ collected in 2016 by the CMS experiment at the CERN LHC from proton-proton collisions at a center-of-mass energy of 13 TeV. The data are found to be consistent with background expectations. Exclusion limits are set in the context of spin-0 two Higgs doublet models, some of which include the presence of dark matter. In the spin-1 heavy vector triplet framework, mass-degenerate W′ and Z′ resonances with dominant couplings to the standard model gauge bosons are excluded below a mass of 2.9 TeV at 95% confidence level.

A search for the decay of the Standard Model Higgs boson into a $ b\\overline{b} $ pair when produced in association with a W or Z boson is performed with the ATLAS detector. The analysed data, corresponding to an integrated luminosity of 36.1 fb$^{−1}$, were collected in proton-proton collisions in Run 2 of the Large Hadron Collider at a centre-of-mass energy of 13 TeV. Final states containing zero, one and two charged leptons (electrons or muons) are considered, targeting the decays Z → νν, W → ℓν and Z → ℓℓ. For a Higgs boson mass of 125 GeV, an excess of events over the expected background from other Standard Model processes is found with an observed significance of 3.5 standard deviations, compared to an expectation of 3.0 standard deviations. This excess provides evidence for the Higgs boson decay into b-quarks and for its production in association with a vector boson. The combination of this result with that of the Run 1 analysis yields a ratio of the measured signal events to the Standard Model expectation equal to 0.90 ± 0.18(stat.)$_{− 0.19}^{+ 0.21}$ (syst.). Assuming the Standard Model production cross-section, the results are consistent with the value of the Yukawa coupling to b-quarks in the Standard Model.

Studies of the spin, parity and tensor couplings of the Higgs boson in the $H \\rightarrow ZZ^{*} \\rightarrow 4 \\ell $ , $H \\rightarrow WW^{*} \\rightarrow e \\nu \\mu \\nu $ and $H \\rightarrow \\gamma \\gamma $ decay processes at the LHC are presented. The investigations are based on $25\\,\\mathrm{fb}^{-1}$ of pp collision data collected by the ATLAS experiment at $\\sqrt{s}=7$ TeV and $\\sqrt{s}=8$ TeV. The Standard Model (SM) Higgs boson hypothesis, corresponding to the quantum numbers $J^{P}=0^{+}$ , is tested against several alternative spin scenarios, including non-SM spin-0 and spin-2 models with universal and non-universal couplings to fermions and vector bosons. All tested alternative models are excluded in favour of the SM Higgs boson hypothesis at more than 99.9 % confidence level. Using the $H \\rightarrow ZZ^{*} \\rightarrow 4 \\ell $ and $H \\rightarrow WW^{*} \\rightarrow e \\nu \\mu \\nu $ decays, the tensor structure of the interaction between the spin-0 boson and the SM vector bosons is also investigated. The observed distributions of variables sensitive to the non-SM tensor couplings are compatible with the SM predictions and constraints on the non-SM couplings are derived.

A bstract There are two tensions related to the Cabibbo angle of the CKM matrix. First, the determinations of V us from K μ 2 , K ℓ 3 , and τ decays disagree at the 3 σ level. Second, using the average of these results in combination with β decays (including super-allowed β decays and neutron decay), a deficit in first-row CKM unitarity with a significance of again about 3 σ is found. These discrepancies, known as the Cabibbo Angle anomaly, can in principle be solved by modifications of W boson couplings to quarks. However, due to SU(2) L invariance, Z couplings to quarks are also modified and flavour changing neutral currents can occur. In order to consistently assess the agreement of a new physics hypothesis with data, we perform a combined analysis for all dimension-six Standard Model Effective Field Theory operators that generate modified W couplings to first and second generation quarks. We then study models with vector-like quarks, which are prime candidates for a corresponding UV completion as they can affect W -quark couplings at tree level, and we perform a global fit including flavour observables (in particular loop effects in ∆ F = 2 processes). We find that the best fit can be obtained for the SU(2) L doublet vector-like quark Q as it can generate right-handed W - u - d and W - u - s couplings as preferred by data.