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Investigation on Higgs physics Group

Investigation on Higgs physics Group. Ye Li Graduate Student UW - Madison. Search for a SM Higgs Boson decaying to W pairs. Matrix Element and Likelihood Ratio Method pp-bar Collisions at 1.96 TeV Integrated Luminosity: 1.1 fb -1 Standard Model Higgs Boson 9 Higgs Mass Hypotheses

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Investigation on Higgs physics Group

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  1. Investigation on Higgs physics Group Ye Li Graduate Student UW - Madison

  2. Search for a SM Higgs Boson decaying to W pairs • Matrix Element and Likelihood Ratio Method • pp-bar Collisions at 1.96 TeV • Integrated Luminosity: 1.1 fb-1 • Standard Model Higgs Boson • 9 Higgs Mass Hypotheses • ranging from 110GeV/c2 to 200GeV/c2 • Channel: two leptons + missing energy

  3. Matrix Element Method: • Make maximum use of the data • Probabilities used as discriminants • Calculated using the LO theoretical prediction for the fully-differential cross-section • 8 variables: two lepton momentums (6 components), two neutrino missing energy (2 quantities) • Compared to the neural network method: discriminant more physics

  4. Likelihood Ratio Discriminator • Directly calculate the event probability: P(xobs;α) • Use PDF, detector acceptance and efficiency function and detector resolution function • Missing information of two neutrinos • Accurate calculation requires the missing info • Smearing due to it is larger than the detector level smearing • Discriminator:

  5. Result (take MH=160 Gev/c2 as the example): • 323 candidates: 286.1 +- 23.3 bg and 3.9 +- 0.3 signal at NNLL calculation • The observed 95% C.L. limit is 1.3pb which is 3.4 times the Standard Model prediction while the median of expected limit is 4.8+2.2-1.4 (systematics included) • See plots at: • http://www-cdf.fnal.gov/physics/new/hdg/HWW_ME/plots.htm

  6. Search for the SM Higgs boson in the ZH->llbb Channel • Small background of mostly real Z + jets events due to the requirement of two leptons and a Z mass constraint • Loosen the tight and loose lepton cuts from standard high PT (top) analyses to improve statistics • 2 Artificial Neural Networks: • One to correct two candidate Higgs jets • The other to maintain signal efficiency and improve signal discrimination

  7. Background: • Bg w/ 2 genuine leptons and 1 b- or c-jet (generator modeling shape) • Bg w/ a fake lepton (use lepton fake rate) • Bg w/ a mistaged light jet (use mistag matrix) • Event Selection:

  8. Result: • The data agrees well with the background • Limit:

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