Search for the higgs boson in association with a z boson
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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

Search for the Higgs boson in association with a Z boson

Giulia Fanti

Michael Mulhearn Selcuk Cihangir


Physics motivation
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


Detection
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


Analysis techniques
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


Mbb analysis muon channel
mbb analysis: muon channel

NN mbb/mjj values

Calculated mbb/mjj values


Further mbb analysis
Further mbb analysis

  • Limit setting

    • Sensitivity to signal

    • SM amplification

    • Collie software

  • 95% confidence scaling factor:

    • Expected: 40.6

    • Observed: 52.4


Z mass comparison
Z-mass comparison

NN zm values:

Calculated zm values:


Matrix element analysis electron transfer functions
Matrix-element analysis: electron transfer functions

  • Finite detector resolution

  • Double gaussian parametrization


Future directions
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


Acknowledgements
Acknowledgements

  • Mike Mulhearn

  • Selcuk Cihangir

  • Sabine Lammers

  • D0 collaboration and Fermilab

  • Department of Energy


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