Higgs Searches at

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• Higgs Searches at
• Tevatron
• Stéphanie Beauceron
• LPNHE - Paris
• on behalf of CDF and DØ Collaborations

Thanks to everybody for their contribution to
this talk
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Outline

• Standard Model Higgs
• Higgs Beyond the Standard Model
• limits on Wbb/WH production
• ?(Zb)/?(Zj) ratio
• limits on H?WW()?ll- production
• limits on neutral Higgs at high tanß
• limits on Non-SM h??? production
• limits on H/H--
• Summary

3636 bunches 396 ns bunch crossing
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Tevatron current and projected performance
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Standard Model Higgs

• Production cross sections are small 0.1 - 1 pb
  depending on MH
• MH ?135 GeV
• gg ? H ? bb dominated by QCD background
• ? searches can be performed in W/Z associated
  production to handle backgrounds
• MH gt135 GeV
• gg ? H? WW()?ll-?? final states can be
  explored at higher masses

Production Cross section
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New EW constraint
Constraint mH in the Standard Model
Old Top mass combination
New Top mass combination using new DØ run I
measurement
Direct searches at LEP2 mHgt114.4 GeV _at_95CL
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Higgs Beyond the Standard Model

• MSSM
• 5 physical Higgs
• Two CP-even scalars h (lighter, SM-like), H
  (heavier)
• CP-odd scalar A
• Charged Higgs pair H
• At tree-level, two free parameters
• Ratio of vacuum expectation values
• One higgs mass
• Other Possibilities
• Left-Right Symmetric, Little Higgs, Higgs Triplet
  models Doubly Charged Higgs
• SM extensions that suppress fermion couplings
• Fermiophobic Higgs
• TopColor Higgs

MSSM Higgs Production Cross section
Large enhancement of rates over HSMbb
MSSM Higgs Main Decay h/H/A?bb 90 h/H/A???
10 H??? 100 (tan?gt1)
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b-jet tagging

• Essential for H?bb searches
• Can make use of the track impact parameter (IP)
  measurements or secondary vertex reconstruction
• CDF performance of sec. vtx. algorithm (after
  kinematics cuts)
• 50 b-tag efficiency for 0.6 light quark
  mis-tag rate in ? lt 1

• DØ in Run II is able to b-tag up to ? lt 2.5
• Performance being improved

b-tagging efficiency vs light quark mis-tag rate
Both experiments are demonstrating good b-tagging
capabilities
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DØ W(?en)bb production (1)

• Motivation
• Background to WH production
• Event selection
• Central isolated e, pT gt 20 GeV
• Missing ET gt 25 GeV
• two jets ET gt 20 GeV, ? lt 2.5
• 2587 evts. in Lint174 pb-1 of data

• Simulations with Alpgen plus Pythia through
  detailed detector response
• Cross sections normalized to MCFM NLO calculations

Good understanding of data
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DØ W(?en)bb production (2)

• Require jets to be tagged, consistent result with
  different b-tagging algorithms

• Observe 8, expect 8.32.2
• Bkgd. dominated by top evts.

Good agreement between data and MC in both cases
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DØ W(?en)bb production (3)

• W Transverse mass of 2 Tagged events, keep event
  with 25 GeVltMT(W)lt125 GeV

We observed 5 events, expect 6.9 ? 1.8 events Set
limits on production of ?(Wbb) lt 20.3 pb at 95
C.L.
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DØ W(?en)bb production (4)

• Optimize Wbb signal by suppressing the top
  production by requiring exactly two jets
• Observe 2 evts., expect 2.50.5

• Sample composition

• Requiring all jets to be b-tag by the 3
  b-tagging algorithms of DØ to reduce the
  background
• ? Observe 2 evts., expect 0.30.1 (Bckd)
  0.60.2 Wbb (Signal)

Probability(B)0.04 Probability(SB)0.23
Standard Model without Wbb disfavored at 2 ?
level
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3 views of high dijet mass (220 GeV) Wbb (WH)
candidate
Vertex view of 2nd candidate
dijet mass (48 GeV)
ETmiss
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DØ W(?en) H(?bb) production

• Observe 2 evts., expect 2.50.5
• In Mass windows 85-135 we observe 0
  events0.54 0.14 expect background0.03 0.01
  WH

Systematics studies
Set limits on production of ?(WH)B(H?bb) lt 12.4
pb for MH 115 GeV at 95 C.L.
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CDF W(?en/mn)H(?bb) production (1)

• Event selection
• Central isolated e/?, pT gt 20 GeV
• Missing ET gt 20 GeV
• Two jets ET gt 15 GeV, ? lt 2
• Veto
• Di-lepton, extra jet
• ? Observe 2072 events in data in Lint162 pb-1
• Simulations performed with Alpgen plus Herwig
  passed through detailed detector response

Good agreement between data and MC
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CDF W(?en/mn)H(?bb) production (2)

• Enrich the b-content of events
• Require at least one b-tagged jet
• ? Observe 62 events in data
• ? Expect 61 5 events
• Main contributions to the bkgd
• Expect 0.3 evts from Higgs
• Signal acceptance of 1.8 for
• MH 110 130 GeV

good agreement between data and MC
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CDF W(?en/mn)H(?bb) production (3)

• Set limits on the Higgs production cross section
  times branching fraction at 95 C.L.
• ?B lt 5 pb
• Systematics studies

Exceeds CDFs Run I limit PRL 79,
3819(1997) ?B lt 14 19 pb for MH 70 120 GeV
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DØ Z(?ee/mm)b production (1)

• Motivation
• Background to ZH production
• Probes PDF of the b-quark
• LO diagrams for ZQ
• Measure cross section ratio
• ?(Zb)/?(Zj)
• Many uncertainties cancel

• Data correspond to integrated lumi. of 184 (ee),
  152 (mm) pb-1
• Event selection
• Isolated e/m with pT gt 15/20 GeV, h lt 2.5/2.0
• Z peak for signal, side bands for bkgd.
  evaluations
• Jet ET gt 20 GeV, h lt 2.5
• At least one b-tagged jet
• Simulations performed with Pythia or Alpgen plus
  Pythia passed through detailed detector response
• Cross sections normalized to data
• Relative b- and c-quark content as given by MCFM
  NLO calculations

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DØ Z(?ee/mm)b production (2)

• Measure cross section ratio Zb/Zj
• 0.024 0.005 (stat) (syst)
• Theory 0.02 hep-ph/0312024
• Systematics studies

• Transverse energy spectrum of b-tagged jets
• QCD and mistag bkgd. estimated from data
• MC Pythia Zb normalized to data

0.005 0.004
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DØ H ? WW() ? ll-nn final states le,m

• Event selection
• Isolated e/m
• pT(e1) gt 12 GeV, pT(e2) gt 8 GeV
• pT(e/m1) gt 12 GeV, pT(e/m2) gt 8 GeV
• pT(m1) gt 20 GeV, pT(m2) gt 10 GeV
• Missing ET greater than
• 20 GeV (ee, em) 30 GeV (mm)
• Veto on
• Z resonance
• Energetic jets
• Simulations done with Pythia passed through
  detailed detector response
• Rates normalized to NLO cross section values
• Data correspond to integrated lumi. of
• 180 (ee), 160 (em) and 150 (mm) pb-1

Data vs MC after evt. preselection
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DØ H ? WW() ? ll-nn final states le, m

• Higgs mass reconstruction not possible due to two
  neutrinos
• Employ spin correlations to suppress the bkgd.
• Df(ll) variable is particularly useful
• Leptons from Higgs tend to be collinear

Azimuthal angle between e and m (after event
pre-selection)
Higgs of 160 GeV
Good agreement between data and MC in all final
states, and all variables examined so far
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DØ H ? WW() ? ll-nn final states le, m
Signal acceptance is 0.02 0.2 depending on
the Higgs mass/final state

• Number of events after selections
• Dominant bkgd. in em sample

Excluded cross section times Branching Ratio at
95 C.L.
Higgs of 160 GeV
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DØ Neutral Higgs Bosons at High Tan? in
Multi-jets Events
(?h,H,A)

• Event Selection
• Multi-jet data sample
• At least 3 jetsET cuts on jets are optimized
  separately for different Higgs mass points, and
  for min. jets required in the event
• ? 3 b-tagged jets
• Look for signal in the invariant mass spectrum
  from the two leading b-tagged jets
• Simulations performed with Pythia or Alpgen plus
  Pythia passed through detailed detector response
• Data correspond to integrated lumi. of 131pb-1

BR( ) 90
Dijet Mass
(Higgs signal at 95 C.L. exclusion limit)
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DØ Neutral Higgs Bosons at High Tan? in
Multi-jets Events
Signal acceptance is 0.2 1.5 depending on
the Higgs mass/final state
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DØ Search for Non-SM Light Higgs in H???

• Data correspond to integrated lumi. of 191 pb-1
• Event selection
• 2 Isolated ? with pT gt 25 GeV, ?lt1.05 (CC) or
  1.5lt?lt2.4 (EC)
• pT?? gt 35 GeV

• Some extensions of SM contain Higgs w/ large
  B(H???)
• Fermiophobic Higgs does not couple to fermions
• Topcolor Higgs couple to top (only non-zero
  fermion coupling)

• Dominant uncertainty in background estimation is
  in the measurement of ? mis-ID rate (30)

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DØ Search for Non-SM Light Higgs in H???

• No clear evidence of excess
• Perform counting experiments on optimized sliding
  mass window to set limit on B(H???) as function
  of M(H)

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CDF Search for H

• H/H-- predicted in models that contain Higgs
  triplets
• Left-Right (LR) symmetric models
• SUSY LR models low mass (100 GeV 1 TeV)

• Event selection
• 1 pair of same sign ee, or ??, or e? in mass
  window of ?10M(H) (3? detector resolution)
• same sign leptons decay contains low SM
  backgrounds, provide clean environment for new
  physics search
• Data correspond to integrated lumi. of 240 pb-1

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CDF Search for H

• Background prediction for M(l l) gt80 GeV
  (gt100 GeV for ee)

• Data observe 0 event

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Prospectives for Higgs

• New study from CDF DØ
• Improvement of the results with a detailed
  simulation.

Statistical power onlySystematics not included
5s discovery 3s evidence 95 CL exclusion
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Summary

• Hunting for Higgs at the Tevatron Run II has
  begun !
• Understanding of the background processes to the
  Higgs production is gradually improving
• Result summary
• ?(Wbb)lt 20 pb
• ?(WH) B(H?bb) lt 12 pb (W?e?)
• ?(WH) B(H?bb) lt 5 pb (W?e? and W???)
• ?(Zb)/ ?(Zj) 0.024 0.005 (stat)
  (syst)
• limits set on ?(H)B(H?WW())
• Search for Neutral Higgs in MSSM
• excludes A and h/H for masses 90-150 GeV/c2 at
  high tan ß (gt100)
• H Search
• Limits 115, 135, 135 GeV/c2 for exclusive HL??
  decays to e?, ee, ??
• Limits 110 GeV/c2 for exclusive HR?? decays to ??
• Search for H???
• Limits are set for the Branching Ratio vs Mass
  for both Fermiophobic and TopColor models
• Already a lot of results and more are coming!

0.005 0.004
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The upgraded CDF and DØ detectors

• New
• silicon detector
• drift chamber
• TOF PID system
• Upgraded
• calorimeter, muon system
• DAQ/trigger
• displaced-vertex trigger

• New (tracking in B-field)
• silicon detector
• fiber tracker
• Upgraded
• calorimeter, muon system
• DAQ/trigger
• (displaced-vertex trigger soon)

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Run I CDF H Search
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DØ H Search (1)

• search assume the H decay branching ratio to
  like-sign muons to be 100.
• Muon ID and analysis requirements
• Make data quality requirements based on official
  good run lists
• Select di-muon trigger events
• Have muon identification requirements based on
• Track segments reconstructed in the muon system,
  isolation from signficant energy deposition in
  the calorimeter and an associated track from the
  central tracking system. The muon momentum is
  taken as the central track momentum
• Muons are required to have pT gt 15 GeV and eta
  lt 2

Dimuon mass spectra at various steps of the event
selection procedure
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DØ H Search (2)

• Search assumes the H decay branching ratio to
  like-sign muons to be 100.
• Confidence level of the signal as a function of
  the H mass,for the left- and right-handed
  Higgs bosons