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Abstract:
We report a search for Standard Model (SM) Higgs boson to WW* production
in the two charged lepton (e, mu) and two neutrino final state in p-pbar
collisions at sqrt(s) = 1.96 TeV. The data were collected with the CDF
II detector at the Tevatron collider at Fermilab and correspond to an
integrated luminosity of approximately 7.1 fb-1. In order to maximize
sensitivity, three neural networks are separately trained to distinguish
signal from background processes in final states with either zero, one,
or two or more jets. For 0-jet events, likelihood ratios based on Matrix
Element calculations are used as additional inputs to the neural network
to further strengthen its discriminating power. In order to take advantage
of the maximum potential signal acceptance, we also consider associated
production with a W or Z boson and Higgs boson production via vector boson
fusion. Additional signal acceptance is gained by including events with
low dilepton invariant mass as a separate search region. We also search
for associated Higgs production in events with same-sign dileptons and
trileptons in the final state. In the opposite-sign event sample we
observe (summing over all jet multiplicities) a total of 2471 candidate
events compared against an expectation of 2520 ± 230 background
events and 42.7 ± 7.2 signal events for a SM Higgs boson with a mass
of 165 GeV/c2. In the opposite-sign low dilepton invariant mass
sample we observe 134 candidate events compared against an expectation
of 127 ± 10 background events and 1.2 ± 0.2 signal events for a SM
Higgs boson with a mass of 165 GeV/c2. In the same-sign event sample
we additionally observe 91 candidate events compared with an expectation
of 90 ± 19 background events and 2.5 ± 0.3 signal events for a
SM Higgs boson with a mass of 165 GeV/c2. In the trilepton event
sample we observe 56 candidate events compared with an expectation of
50.2 ± 6.1 background events and 1.8 ± 0.2 signal events for a
SM Higgs boson with a mass of 165 GeV/c2. Based on these samples, we
determine an observed 95% C.L. upper production limit of 0.92 times the
SM prediction at NNLL for a Higgs mass of 165 GeV/c2 to be compared
with the value for the median of the expected limit (0.93). Results
for eighteen other Higgs mass hypotheses ranging from 110 GeV/c2 to
200 GeV/c2 are also presented. We exclude at the 95% C.L. a SM Higgs
boson in the mass range between 158 and 168 GeV/c2. We also perform a
separate search for a SM Higgs boson considering only the gg to H to WW
production process. In this case we circumvent theoretical cross section
uncertainties and obtain 95% C.L. upper limits on the production cross
section times branching ratio for this process. We extract these limits
for twenty-nine different Higgs mass hypotheses in the range between
110 GeV/c2 and 300 GeV/c2. Using these limits we place constraints on
a potential Higgs mass in the scenario of a fourth sequential generation
of fermions with large masses, which would lead to significantly enhanced
gg to H production. For this scenario we exclude at the 95% C.L. a
SM-like Higgs boson in the mass range between 124 and 202 GeV/c2.
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