search for the higgs boson in association with a z boson
DESCRIPTION
Search for the Higgs boson in association with a Z boson. Giulia Fanti. Michael Mulhearn Selcuk Cihangir. Physics motivation. Standard Model Missing piece Higgs mechanism electroweak symmetry breaking origin of mass implies existence of Higgs boson Higgs decays m H >135: - PowerPoint PPT PresentationTRANSCRIPT
Search for the Higgs boson in association with
a Z bosonGiulia Fanti
Michael Mulhearn Selcuk Cihangir
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Physics motivation• Standard Model
– Missing pieceHiggs mechanism• electroweak symmetry breaking • origin of mass• implies existence of Higgs boson
• Higgs decays– mH>135:
– mH<135: • Large background at Tevatron
• ZH: possible production mechanism–
– LEP excluded mH<114 GeV/c2
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Detection• Electrons/positrons
– Tracks in tracker– EM calorimeter
• Jets– Energy in calorimeter– Tracks in the tracker– B-tagging
• Silicon trackers• Displaced vertices
• Muons/antimuons– Exterior muon
chambers
Image courtesy of Fermilab: http://www.fnal.gov/pub/now/live_events/explain_det_dzero.html
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Analysis Techniques
• Preselection– Kinematic cuts, b-tagging
• Start with mbb analysis– Single most discriminating variable
• Multivariate techniques– Neural networks– Matrix element analysis
• Standard Model: matrix elements• Transfer functions: jets, leptons• Hope to improve sensitivity
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mbb analysis: muon channelNN mbb/mjj values Calculated mbb/mjj values
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Further mbb analysis
• Limit setting– Sensitivity to
signal– SM amplification– Collie software
• 95% confidence scaling factor:– Expected: 40.6– Observed: 52.4
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Z-mass comparison
NN zm values:
Calculated zm values:
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Matrix-element analysis: electron transfer functions
• Finite detector resolution• Double gaussian parametrization
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Future directions
• Matrix element analysis– Technique developed on Run IIA data for muon
channel– Muon channel
• Understand kinematics of muon Run IIB data• Have transfer functions for jets, muons
– Electron channel• Fitted electron transfer functions
– Ready to apply ME analysis to both channels
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Acknowledgements
• Mike Mulhearn• Selcuk Cihangir• Sabine Lammers• D0 collaboration and Fermilab• Department of Energy