Study of (W/Z)H production and Higgs boson couplings using H→ W W^∗ decays with the ATLAS detector

Abstract: A search for Higgs boson production in association with a W or Z boson, in the H→ W W^∗ decay channel, is performed with a data sample collected with the ATLAS detector at the LHC in proton-proton collisions at centre-of-mass energies √s=7$$ \sqrt{s}=7 $$ TeV and 8 TeV, corresponding to integrated luminosities of 4.5 fb⁻¹ and 20.3 fb⁻¹, respectively. The WH production mode is studied in two-lepton and three-lepton final states, while two- lepton and four-lepton final states are used to search for the ZH production mode. The observed significance, for the combined W H and ZH production, is 2.5 standard deviations while a significance of 0.9 standard deviations is expected in the Standard Model Higgs boson hypothesis. The ratio of the combined W H and ZH signal yield to the Standard Model expectation, μ_{V H} , is found to be μ_V H = 3.0_{− 1.1}^{+ 1.3}(stat.)_{− 0.7}^{+ 1.0}(sys.) for the Higgs boson mass of 125.36 GeV. The W H and ZH production modes are also combined with the gluon fusion and vector boson fusion production modes studied in the H → W W^∗ → ℓνℓν decay channel, resulting in an overall observed significance of 6.5 standard deviations and μ_{ggF + VBF + VH} = 1. 16_{− 0.15}^{+ 0.16}(stat.)_{− 0.15}^{+ 0.18}(sys.). The results are interpreted in terms of scaling factors of the Higgs boson couplings to vector bosons (κ_V ) and fermions (κ_F ); the combined results are: |κ_V| = 1.06_{− 0.10}^{+ 0.10}, |κ_F| = 0. 85_{− 0.20}^{+ 0.26}.[Figure not available: see fulltext.]