CDF Logo CDF Search for Higgs to WW* Production using a Combined Matrix Element and Neural Network Technique
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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.

 

Supporting Documents:

  • The results were first presented at Moriond EWK 2011
  • More details are provided in the public note
  • Previous multivariate result with 5.9 fb-1: html
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    General Remarks:

  • The preliminary results were blessed in the Higgs group on March 4, 2011
  • Please contact us if you have any questions about including these results in a presentation
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     Updated by Eric James
    For problems or questions regarding this website contact jameseb_AT_fnal.gov
    Last updated: March 9 2011.