Constraints on the off-shell Higgs boson signal strength in the high-mass ZZ and WW final states with the ATLAS detector

ATLAS, Collaboration; Beck, Hans Peter; Cervelli, Alberto; Ereditato, Antonio; Haug, Sigve; Kabana, Sonja; Meloni, Federico; Mullier, Geoffrey André Adrien; Pretzl, Klaus-Peter; Stramaglia, Maria Elena; Stucci, Stefania; Weber, Michael (2015). Constraints on the off-shell Higgs boson signal strength in the high-mass ZZ and WW final states with the ATLAS detector. European physical journal. C - particles and fields, C75(7), p. 335. EDP Sciences 10.1140/epjc/s10052-015-3542-2

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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→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 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 Γ H /Γ SM H 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.

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