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Search for the Higgs boson in association with a Z boson

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:

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Search for the Higgs boson in association with a Z boson

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  1. Search for the Higgs boson in association with a Z boson Giulia Fanti Michael Mulhearn Selcuk Cihangir

  2. Physics motivation • Standard Model • Missing pieceHiggs 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

  3. 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

  4. 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

  5. mbb analysis: muon channel NN mbb/mjj values Calculated mbb/mjj values

  6. Further mbb analysis • Limit setting • Sensitivity to signal • SM amplification • Collie software • 95% confidence scaling factor: • Expected: 40.6 • Observed: 52.4

  7. Z-mass comparison NN zm values: Calculated zm values:

  8. Matrix-element analysis: electron transfer functions • Finite detector resolution • Double gaussian parametrization

  9. 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

  10. Acknowledgements • Mike Mulhearn • Selcuk Cihangir • Sabine Lammers • D0 collaboration and Fermilab • Department of Energy

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