investigation on cdf higgsyli/web_folder/... · – 8 variables: two lepton momentums (6...
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Investigation on Higgs physics Group
Ye LiGraduate 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/c2 to 200GeV/c2
• 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(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:
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• 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
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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 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
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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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