The European Physical Journal C > 2015 > 75 > 7 > 1-34
Constraints on the off-shell Higgs boson signal strength in the high-mass ZZ and WW final states with the ATLAS detector
Source
Abstract
Measurements of the ZZ and WW final states in the mass range above the $$2m_Z$$ 2 m Z and $$2m_W$$ 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 $$ZZ \rightarrow 4\ell $$ Z Z → 4 ℓ , $$ZZ\rightarrow 2\ell 2\nu $$ Z Z → 2 ℓ 2 ν and $$WW\rightarrow e\nu \mu \nu $$ 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 $$^{-1}$$ - 1 at a collision energy of $$\sqrt{s}=8$$ s = 8 TeV. Using the $$CL_s$$ 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 $$gg\rightarrow ZZ$$ g g → Z Z and $$gg\rightarrow WW$$ 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 $$\Gamma _H/\Gamma _H^{\mathrm {SM}}$$ 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 $$gg\rightarrow VV$$ 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.
Identifiers
journal ISSN : | 1434-6044 |
journal e-ISSN : | 1434-6052 |
DOI | 10.1140/epjc/s10052-015-3542-2 |