Investigation on Higgs physics Group Ye Li Graduate Student UW - - - PowerPoint PPT Presentation

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Mar 17, 2024 40 likes •161 views

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

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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/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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