Abstract
A measurement of off-shell Higgs boson production in the ZZ→4ℓ and ZZ→2ℓ2ν decay channels, where ℓ stands for either an electron or a muon, is performed using data from proton–proton collisions at a centre-of-mass energy of s=13 TeV. The data were collected by the ATLAS experiment in 2015 and 2016 at the Large Hadron Collider, and they correspond to an integrated luminosity of 36.1fb−1. An observed (expected) upper limit on the off-shell Higgs signal strength, defined as the event yield normalised to the Standard Model prediction, of 3.8 (3.4) is obtained at 95% confidence level (CL). Assuming the ratio of the Higgs boson couplings to the Standard Model predictions is independent of the momentum transfer of the Higgs production mechanism considered in the analysis, a combination with the on-shell signal-strength measurements yields an observed (expected) 95% CL upper limit on the Higgs boson total width of 14.4 (15.2) MeV.
Highlights
The observation of the Higgs boson by the ATLAS and CMS experiments [1,2] at the Large Hadron Collider (LHC) marks a milestone towards the understanding of the mechanism of electroweak (EW) symmetry breaking [3,4,5]
Given that the QCD corrections for the off-shell signal processes have only been calculated inclusively in the jet multiplicity, the analysis is performed inclusively in jet observables and the event selection is designed to minimise the dependence on the momentum of the Z Z system, which is sensitive to the jet multiplicity
Systematic uncertainty sources impacting the analysis of both channels can be divided into two categories: uncertainties in the theoretical description of the signal and background processes and experimental uncertainties related to the detector or to the reconstruction algorithms
Summary
The observation of the Higgs boson by the ATLAS and CMS experiments [1,2] at the Large Hadron Collider (LHC) marks a milestone towards the understanding of the mechanism of electroweak (EW) symmetry breaking [3,4,5]. It is assumed that any new physics which modifies the off-shell signal strength and the off-shell couplings does not modify the relative phase of the interfering signal and background processes. ATLAS obtained an observed (expected) upper limit on the off-shell Higgs boson signal strength (μoff-shell) in the range of 5.1–8.6 (6.7–11.0) [26], using the Z Z and. Given that the QCD corrections for the off-shell signal processes have only been calculated inclusively in the jet multiplicity, the analysis is performed inclusively in jet observables and the event selection is designed to minimise the dependence on the momentum of the Z Z system, which is sensitive to the jet multiplicity
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