Searches for the Higgs Boson

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• Searches for the Higgs Boson
• Matthew Herndon, University of Wisconsin Madison
• 34th International Conference on High Energy
  Physics

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Searches for the Higgs Boson

• Introduction
• Tools of the Trade
• BSM Higgs Searches
• SM Higgs Searches
• LHC Potential
• Conclusions

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Electroweak Symmetry Breaking

• Consider the Electromagnetic and the Weak Forces
• Coupling at low energy EM ?, Weak ?/(MW,Z)2
• Fundamental difference in the coupling strengths
  at low energy, but apparently governed by the
  same dimensionless constant
• Difference due to the massive nature of the W and
  Z bosons
• SM postulates a mechanism of electroweak symmetry
  breaking via the Higgs mechanism
• Results in massive vector bosons and mass terms
  for the fermions
• Directly testable by searching for the Higgs boson

A primary goal of the Tevatron and LHC
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Electroweak Constraints

• Higgs couples strongly to massive particles
• Introduces corrections to W and top masses -
  sensitivity Higgs mass

SM LEP Direct search mH gt 114GeV SM indirect
constraint mH lt 160GeV
We know where to look
SUSY Higgs looks interesting
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Colliders and Experiments

• Tevatron 2TeV pp collider - general purpose
  detectors CDF, D0
• LHC 14TeV pp collider - general purpose
  detectors ATLAS, CMS

• Excellent lepton Id
• Good to excellent calorimeters for jet and MET
  reconstruction
• Excellent silicon detectors for b jet
  identification
• Potential for Higgs discovery in dedicated B
  physics experiments
• Babar, Belle, LHCB

Tevatron results in this talk
Tevatron SM Higgs mass exclusion and perhaps
evidence
LHC Observation over full mass range. Study
Higgs properties
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Tools Triggers

• Triggers Extract handful of Higgs events from a
  total background 10-11 orders of magnitudes larger

• Primary triggers High pT?e and ?
• Dedicated Z triggers
• JetMET triggers modes with no charged leptons
• CDF JetMET triggers supplement lepton triggers
  for gaps in coverage
• Dedicated ? triggers
• trackMETCal Energy

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Tools Lepton Id

• Dedicated lepton detectors for e/?
• Improvements in lepton Id
• DØ excellent muon acceptance with OR of all muon
  detectors/triggers
• CDF Supplements detector gaps with use of
  isolated tracks
• CDF/DØ applying ? Id in both SM and beyond the SM
  Higgs searches
• Lepton types well understood from large
  calibration samples

Maximizing Higgs acceptance
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Tools b quark jets

• b jet tagging?
• DØ NN tagger with several operating points
• CDF Secondary Vertex tagger, jet probability
  tagger, and NN flavor separators
• 50-70 Efficient with 0.3-5 mistag rate

• Improvements in jet energy(dijet mass) resolution
• H1 algorithm and NN based corrections

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Tools Backgrounds

• Every SM process is a background to Higgs
• Discovery analyses
• WW, WZ, ZZ, single top, and even top pairs
• Total and differential cross section
  measurements
• QCD dijets, Wb, Wc, Zb
• Critical to Higgs
• Constrain background predictions
• Testing ground for tools and techniques
• Control regions

Higgs search built on a foundation of the entire
collider physics program
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BSM Higgs

• Many Beyond the Standard Model Higgs
  Possibilities
• SUSY Higgs tan? enhanced couplings to b quarks
  and tau leptons
• h, H, A, H, H- or alternative models with doubly
  charged Higgs
• Fermiophobic Higgs with enhanced couplings to W
  bosons or photons

f0 h/H/A
Observable at Tevatron or LHC
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BSM Higgs ??bb

• 3b channel b??bbb.
• Di-b-jet background too large in ??bb channel
• Search for peak in di-b-jet mass distribution of
  leading jets
• Key issue understanding the quark content of the
  3 jets
• CDF Secondary vertex tagger and vertex mass
• D0 NN tagger
• Background Simulation and data driven studies

• No Evidence for SUSY Higgs
• Limits tan? vs mA
• 3b search very sensitive with certain SUSY
  parameter choices

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BSM Higgs ????

• ???? and b??b?? channels
• ?? pure enough for direct production search
• DØ adds associated production search b??b??
• Key issue understanding ? Id efficiency
• Large calibration samples W for Id optimization
  and Z for confirmation of Id efficiency

• No Evidence for SUSY Higgs
• Limits tan? vs mA
• ???? generally sensitive at high tan?

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Other BSM Higgs Searches

• Fermiophobic Higgs
• Scenarios where Higgs coupling to fermions is
  small
• DØ H??? (also SM search)
• At lower mass large BR(H???) and order magnitude
  100fb cross section
• Key issue understanding QCD background uses
  excellent calorimeter

• Other BSM Higgs Searches

• WH?WWW (also SM), charged Higgs, decays to and
  from top

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SM Higgs Production and Decay

• High mass H?WW?l?l? decay available
• Take advantage of large gg?H production cross
  section
• Low Mass H?bb background dominates
• Use associated production with W or Z for
  background discrimination
• WH?l?bb, ZH???bb (METbb), ZH?llbb
• Also VBF Production, VH?qqbb, H???(with 2jets),
  H???, WH-gtWWW, ttH

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Wheres the Beef Higgs
Macroscopic Higgs Event Counts
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SM Higgs ZH?llbb

• ZH?llbb - signature two leptons and b jets
• Backgrounds Z b jets
• Key issue Maximize lepton acceptance and b
  tagging efficiency
• Innovations CDF/DØ Extensive use of loose b
  tagging
• CDF Use of isolated tracks and
  calorimeter only electrons
• Use of MET to correct jet energies,
  New ME analysis
• DØ XXX

Results at mH 115GeV 95CL Limits/SM
Analysis Lum (fb-1) Higgs Events Exp. Limit Obs. Limit
CDF NN 2.4 XXX 11.8 11.6
CDF ME(120) 2.0 XXX 15.2 11.8
DØ NN 2.X XXX XXX XXX
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SM Higgs VH?METbb

• ZH???bb, WH?l?bb(l not detected) - signature MET
  and b jets
• Backgrounds QCD b jets and mistagged light quark
  jets
• Key issue Building a model of the QCD background
• Shape from 0 and 1 tag data samples with tag and
  mistag rates applied
• Innovations CDF/DØ Use of track missing pT to
  define control regions and
• suppress backgrounds, CDF Uses of H1 Jet
  Algorithm

Results at mH 115GeV
Analysis Lum (fb-1) Higgs Events Exp. Limit Obs. Limit
CDF NN 2.1 7.3 6.3 7.9
DØ BDT 2.1 3.7 8.4 7.5
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SM Higgs WH?l?bb

• WH?l?bb - signature high pT lepton, MET and b
  jets
• Backgrounds Wbb, Wqq(mistagged), single top,
  Non W(QCD)
• Key issue estimating Wbb background
• Shape from MC with normalization from control
  regions
• Innovations CDF leptons Id with isolated
  tracks, ME search with NN jet corrections
• DØ dedicated WH???bb search

Results at mH 115GeV
Analysis Lum (fb-1) Higgs Events Exp. Limit Obs. Limit
CDF NN 2.7 8.3 5.8 5.0
CDF MEBDT 2.7 8.3 5.6 5.7
DØ NN 2.X XX XX XX
DØ WH???bb 2.X XX XX XX
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SM Higgs H?WW

• H?WW?l?l? - signature Two high pT leptons
• Backgrounds WW and top in 2 jet bin
• Key issue Maximizing lepton acceptance
• Innovations CDF/DØ Combination of ME and NN
  approaches
• CDF Inclusion of acceptance from VH and VBF
  in 1 and 2 jet bins

Spin correlation Charged leptons go in the same
direction
Results at mH 160GeV
Analysis Lum (fb-1) Higgs Events Exp. Limit Obs. Limit
CDF MENN 3.0 16.6 1.8 1.7
DØ MENN 2.X XXX 2.3 2.3
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Other SM Higgs Searches

• CDF and DØ implement searches in every viable
  mode
• CDF/DØ WH?WWW same sign leptons
• Adds sensitivity at high and middle masses. Also
  Fermiophobic Higgs search
• CDF VH?qqbb 4 Jet mode.
• CDF H??? with 2jets
• Simultaneous search for Higgs in VH, VBF and gg?H
  production modes
• Interesting bench mark for LHC
• DØ H? ??
• Also model independent and fermiophobic search
• DØ ttH
• Rest of slide devoted to this since its new

Analysis Exp. Limit
CDF WH?WWW 33
DØ WH?WWW XX
CDF VH?qqbb 37
CDF H??? 25
DØ H??? 23
DØ ttH XX
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SM Higgs Limits

• Display of all CDF and D0 expected limits on one
  plot!
• Combination group is working on this

• Limits calculating and combination
• Using Bayesian and CLs methodologies.
• Incorporate systematic uncertainties using
  pseudo-experiments
• Backgrounds can be constrained in the fit

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SM Higgs Combination
2.X_at_115GeV
0.X_at_160GeV
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LHC Prospects

• Three LHC slides
• Will design them based on the parallel session
• Emphasis not placed on H?WW?l?l?

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Conclusions

• The Higgs boson search is in its most exciting
  era ever
• The Tevatron experiments have achieved
  sensitivity to the SM Higgs boson production
  cross section
• In addition there is strong sensitivity to beyond
  the SM Higgs
• With the advent of the LHC we will have the
  potential to observe the Higgs boson and study
  its properties.
• For the first time since the end of LEP we have
  direct information on the SM Higgs mass

SM Higgs Excluded mH 160-170GeV
I hope!