Constraints on the off-shell Higgs boson signal strength in the high-mass ZZ and WW final states with the ATLAS detector
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KünyeAad, G., Abbott, B., Abdallah, J., Abdinov, O., Aben, R., Abolins, M. … ATLAS Collaboration. (2015). Constraints on the off-shell Higgs boson signal strength in the high-mass ZZ and WW final states with the ATLAS detector.The European Physical Journal C, 75(7), 1-34. http://dx.doi.org/10.1140/epjc/s10052-015-3542-2
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 -> 2l2 nu and WW -> e nu mu nu 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 root 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 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(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.