onstraints 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?2mZ?and?2mW?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→4?,?ZZ→2?2ν?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?CLs?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 QCD 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 production, a combination with the on-shell measurements yields an observed (expected) 95\% CL upper limit on?ΓH/ΓSMH?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.