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

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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/c 2 to 200GeV/c 2 Channel: two leptons + missing energy

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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

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Likelihood Ratio Discriminator –Directly calculate the event probability: P(x obs ;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:

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Result (take M H =160 Gev/c 2 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

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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 P T (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

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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:

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Result: –The data agrees well with the background –Limit:

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