D

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DØ Higgs Physics Results

• Jyothsna Rani
• Tata Institute of Fundamental Research
• Mumbai, India
• on behalf of the DØ Collaboration
• Lake Louise Winter Institute
• 20th 26th February 2005
• Alberta, Canada

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Outline

• Standard Model Higgs searches
• Associated production of H with W
• H ? W W for mH gt 135 GeV
• Non Standard Model Higgs searches
• MSSM Neutral Higgs in (b)bh?(b)bbb
• final state

NEW
Results presented here are based on 174 260
pb-1
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Missing Piece in Standard Model

• The mass of elementary particles in the Standard
  Model is explained by the presence of Higgs
  boson.
• The mass of the Higgs boson is not predicted in
  SM.
• Precision measurements constrain
• 114 GeV lt mH lt 260 GeV
• Tevatron provides
• Indirect search
• Precision mt and mw measurements
• Direct searches
• SM Higgs
• non-SM Higgs

LEP
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SM Higgs Decays

• Search strategies are a function of
• Decay modes and
• Production channels
• Two search strategies at Tevatron
• Low mass Higgs searches mH lt 135 GeV
• H ? b?b
• High mass Higgs searches mH gt 135 GeV
• H ? W W

Excluded at LEP
Higgs Mass (GeV/c2)
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SM Higgs Production at Tevatron
Gluon Fusion gg ? H ? 1pb At low mass (H
? b?b ), high QCD background. At
High mass usable with H? W W decay
mode. Associated Production WH or ZH ?
0.1pb Used at low mass with H ? b?b decay mode.
Excluded at LEP
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Identifying b-jets
Performance of Secondary Vertex Tagging algorithm

• Secondary Vertex.
• Large Impact Parameter
• of the tracks.

Tagging the b-jets is important for H ? b?b decay
modes.
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SM Higgs Search WH ? ln bb

• Search Strategy
• Use sample of W(e?)2 b-tagged jets.
• Require exactly 2 jets to suppress top
  background.
• 4.4 ? 1.2 events expected and 6 events observed.
• ?(WH)BR(H? b?b ) lt 9.0 pb _at_ 95 C.L. for mH 115
  GeV
• Also ?(W b?b ) lt 6.6 pb _at_ 95 C.L. for pT(b) gt 20
  GeV

115 GeV
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SM Higgs Search H ? WW ? ln ln

• Search strategy
• 2 high pT leptons and MET
• WW comes from spin 0 Higgs
• leptons prefer to point in the
• same direction

? BR(H?WW) lt 5.7pb _at_ 95 C.L. for mH160
GeV
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Higgs in Minimal Supersymmetry

• MSSM has pairs of Higgs doublet fields
• Hu couples to up-type quarks and leptons and Hd
  to down-type
• tan ? ltHugt/ltHdgt
• 5 Higgs particles after EWSB h0, H0, A0, H,
  H-
• h0 is predicted to be light
• m h0 lt 130 GeV (MSSM)

tan ?
h0, H0, A0 production
_at_ Tevatron
Zb ? Probe of b-quark PDF ? bh and single
top production ?(Zb) / ?(Zj) 0.023 ?
0.005 (DØ hep-ex/0410078) 0.018 ?
0.004 (CTEQ6 prediction)
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Higgs Production and Large tan ?

• Large tan? ? enhanced bbh/H/A
• At tree level , cross section rises like tan2?
• A and h/H are produced simultaneously.

Total cross section
A
h
CP odd Higgs
CP even Higgs
H
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Analysis Overview

• Signal
• at least 3 b-tagged jets
• Invariant mass of two leading
• pT jets
• Backgrounds
• QCD heavy flavor bbjj, ccjj, cccc, bbcc,
  bbbb
• QCD fakes jjjj
• Other Z(bb,cc), tt
• Kinematic cuts
• Cut on pT of leading jets
• (Optimized for each Higgs mass)
• Search for an excess of events
• in di-jet invariant mass distribution
• consistent with a Higgs signal
• shape.

Di-jet invariant mass in ? 3b-tagged events
260 pb-1
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(b)bh Limits on ? and tan?
NEW
260 pb-1
260 pb-1
Two benchmark scenarios? Max Mixing Xt At -
?cot? ?6 No Mixing Xt 0 For mA 120 GeV
? lt 31 pb-1 _at_ 95 C.L. and tan? lt
55 _at_ 95 C.L. (Max Mixing)
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Summary

• Higgs hunting at Tevatron is ongoing.
• SM Higgs searches
• DØ placed limits on cross section on WH(? bb).
• ?(Zb) / ?(Zj) ratio has been measured.
• Understanding of backgrounds is improving.
• H ? W W searches placed limits on cross section.
• Non SM Higgs searches
• Enhanced Higgs production at high tan? is used to
  exclude (mA, tan?) plane.
• Expect substantial improvements in Higgs hunting
  with 0.6 fb-1 already on tapes.