Constraints on the Off-Shell Higgs Boson Signal Strength in the High-Mass ZZ and WW Final States with the ATLAS Detector


Measurements of the ZZ and WW final states in the mass range above the 2m(Z) and 2m(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 → 4ℓ, ZZ → 2ℓ2ν and WW → eνμν 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 CL(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 → ZZ and gg → WW 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 (formula presented) 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 → VV 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.



Higgs bosons, Proton-proton interactions, Standard Model, Luminescence, Particles (Nuclear physics), Quantum field theory


CC BY 4.0 (Attribution), ©2015 CERN, for the ATLAS Collaboration