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Search for Higgs boson production in oppositely charged dilepton and missing energy final states in 9.7 fb-1 of ppbar collisions at sqrts = 1.96 TeV

We present a search for Higgs boson in final states with two oppositely charged leptons and large missing transverse energy as expected in H -> WW -> lvlv decays. The events are selected from the full Run II data sample of 9.7 fb-1 of ppbar collisions collected with the D0 detector at the Fermilab Tevatron Collider at sqrt s = 1.96 TeV. To validate our search methodology, we measure the non-resonant W W production cross section and find sigma_WW = 11.6 +/- 0.7 pb, in agreement with the standard model prediction. In the Higgs boson search, no significant excess above the background expectation is observed. Upper limits at the 95% confidence level on the Higgs boson production cross section are therefore derived. Within the standard model, the Higgs boson mass range 159 < MH < 176 GeV is excluded while the expected exclusion sensitivity is 156 < MH < 172 GeV. For a mass hypothesis of MH = 125 GeV, we exclude Higgs boson production cross sections 4.1 times larger than the standard model expectation, which is compatible with the presence of a Higgs boson at this mass. Within a theoretical framework with a fourth generation of fermions, the mass range 125 < MH < 218 GeV is excluded. The search results are also interpreted in the context of fermiophobic Higgs boson couplings, which yields an exclusion of fermiophobic Higgs boson production cross sections 3.1 times larger than the expectation for MH = 125 GeV.