Searches for the Standard Model Higgs at the Tevatron

1
Searches for the Standard Model Higgs at the
Tevatron

• presented by
• Per Jonsson
• Imperial College London
• On behalf of the CDF and DØ Collaborations

2
Outline

• Introduction
• Higgs ? bb (low mass)
• ZH ? ??bb
• WH ? l?bb
• Higgs ? WW (high mass)
• WH ? WWW
• H ? WW
• Limits
• combination

New results!
New result!
New result!
3636 bunches 396 ns bunch crossing
Only new results since last years Moriond are
shown
Per Jonsson - Imperial College London
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Tevatron Performance

• Currently in shutdown
• Silicon and Trigger upgrades

4-8 fb-1 expected by end of 2009
This talk 261-950pb-1
Run I
Per Jonsson - Imperial College London
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The DØ and CDF detectors

• The Standard Model Higgs Boson is
• Key part of Electro-Weak symmetry breaking
• A scalar with the Higgs mass as the only free
  parameter
• DØ and CDF constrain the SM Higgs boson mass
• Indirectly Top and W mass measurements
• Directly Search for Higgs boson production

Per Jonsson - Imperial College London
5
EW constraints on Higgs
LEPEWWG 18/03/06
68 CL
mH 89 45 -30 GeV
GeV
GeV
mHlt175 GeV _at_95CL (lt 207 GeV if LEP2 limit incl.)
A light Higgs is favored
Per Jonsson - Imperial College London
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SM Higgs Production

• Production cross sections are small 0.1-1 pb
  depending on mH
• 1 in 1012 pp events is a Higgs
• MHlt 135 GeV decay to bb
• gg ?H ?bb overwhelmed by QCD background
• searches can be performed in W/Z associated
  production with lower background
• Best channels
• WH?l?bb, ZH???bb
• MH gt 135 GeV decay to WW
• gg ?H ?WW() ?ll-??
• WH ?WWW()
• final states can be explored

We probably have a Higgs in our data already!
Per Jonsson - Imperial College London
7
Backgrounds and Tools

• Understanding and modeling of background is
  critical
• Especially so for advanced analysis techniques
• Electroweak backgrounds
• (W, Z, WZ, WW, Top)
• Monte Carlo distributions normalized to (N)NLO
  cross sections
• QCD and instrumental background taken from real
  data control samples

• Measurements also rely on
• Jet reconstruction
• B-tagging
• Use track impact parameter (IP) measurements or
  secondary vertex reconstruction

IP

• Lepton identification
• Missing transverse energy

Both detectors are delivering the excellent
performance needed
Per Jonsson - Imperial College London
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Z/g ?ee jets

New result!
For details see Gavins talk yesterday.

• Comparison of jet multiplicities and
  distributions in data and MC
• Pythia 6.319 vs. Sherpa 1.0.6
• Sherpa Matrix Element Parton showers, using
  CKKW algorithm

• Event selection includes
• Electron pT gt 25 GeV, hlt2.5/1.1
• 70 GeV lt Mee lt 120 GeV

Sherpa agrees well with data upto njet4
L950 pb-1
L950 pb-1
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ZH ???bb

ET1 100.3 GeV ET2 54.7 GeV ETmiss 144.8
GeV Mjj 82.1 GeV

• Event selection includes
• 1 tagged b-jets
• Two jets with ET gt 60/25 GeV
• ET miss gt 70 GeV
• Backgrounds
• W/Z heavy flavour jets
• QCD
• Di-bosons
• Mis-tagged b-jets
• Top pairs

• MH 120 GeV, 80 lt mjj lt 120 GeV
• 6 events observed
• 4.36 /- 1.02 predicted
• s95 4.5 pb

10
ZH ???bb

New result!

• Improved event selection includes
• Two acoplanar jets with
• ET gt 20 GeV
• ETmiss gt 50 GeV
• Sum of scalar jet ET lt 240 GeV
• Separate analysis for single and double b-tagged
  events
• Increased statistics

• mH 115 GeV, 75 lt mjj lt 125 GeV
• 11 events observed
• 9.4 /- 1.8 predicted
• s95 4.3 pb
• Same analysis for WH? lnbb with missed lepton
  improves the WH limit

L261 pb-1
L261 pb-1
1 b-tag
2 b-tags
11
WH?l?bb , (le,m)

b jet
b jet
n
e/m

• Muon and electron channel combined
• 1 or 2 tagged b-jets
• electron or muon with pT gt 20 GeV
• ETmiss gt 20 GeV

• Main backgrounds
• W jets
• Top pairs
• di-bosons (WW, WZ etc.)

Per Jonsson - Imperial College London
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WH?l?bb, (le,m)

New result!

• New muon analysis
• Re-optimized electron analysis
• Separate single and double
• b-tag analysis
• Event selection includes
• Central isolated e/m
• pT gt 20 GeV
• Missing ET gt 25 GeV
• two jets
• ET gt 20 GeV, ? lt 2.5
• One or two tagged b-jets
• Limit from combined channels
• mH 115 GeV, 85 lt mjj lt 140 GeV
• 6 (32 ST) events observed
• 9.3 (45.1 ST) predicted
• s95 2.4 pb

Per Jonsson - Imperial College London
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WH?WWW()?ll?? qq, (le,???

• Event selection includes
• Two isolated like signed leptons (ee,em,mm)
• pT gt 15 GeV
• ETmiss gt 20 GeV
• s95 (mH115 GeV) 3.88 pb

L363 pb-1
Mainly di-bosons (WZ)
observed expected
ee 1 0.70 /- 0.08
em 3 4.32 /- 0.23
mm 2 3.72 /- 0.75
CDF 194 pb-1
Per Jonsson - Imperial College London
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H?WW()?ll-??, (le,??

• Higgs mass reconstruction not possible due to two
  neutrinos
• Employ spin correlations to suppress the
  background
• ??(ll) variable is particularly useful
• Charged leptons from Higgs are collinear
• Event selection includes
• Two leptons (e/?)
• pT gt 20/10 GeV
• Missing ET greater than
• MH/4

mH 130 GeV
mH 160 GeV
Per Jonsson - Imperial College London
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H?WW()?ll-?? (le,??

New result!

• L 950 pb-1
• ee and em channels
• Event selection includes
• Isolated e/?
• pT(e1, e2) gt 15, 10 GeV
• pT(e/?1) gt 15 GeV,
• pT(e/?2) gt 10 GeV
• Missing ET greater than
• 20 GeV (ee, e?)
• Veto on
• Z resonance
• Energetic jets
• MH 120 GeV
• 31 events observed
• 32.7 /- 2.3 (stat) predicted
• Bkg systematic uncertainty 15

After cuts
ee
em
160 GeV Higgs (x 10)
Per Jonsson - Imperial College London
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Combined limit

New result!

• New combined limit from all SM Higgs search
  channels!
• 14 orthogonal search channels (incl. single and
  double-tag analyses and
• WH? lnbb w. missed lepton)
• Full account taken of systematic uncertainties
• High mass region benefits from H?WW analyses

• Currently a factor 15 away from
• mH 115 GeV
• With L 2 fb-1, both experiments, NN b-tagging,
  NN analyses, track-cal jets, increased
  acceptance, new channels, full cross efficiency,
  and reduced systematics
• Cross section factor 1.2

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Limits
18
Summary

• The Tevatron and the experiments are performing
  well
• A wide range of Standard Model Higgs searches
  have been performed by both CDF and D0 with up to
  1 fb-1 RunII data
• No deviation from the SM background expectation
  observed
• Work underway to improve sensitivity
• First combination of all channels from D0
• Very exciting prospects for the future
• Sensitivity to m H gt 114 GeV starts at 2 fb-1
• Exclusion up to 180 GeV possible with 8 fb-1

Many results already and more with increased
stats are coming soon!
Per Jonsson - Imperial College London
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Back-up slides
20
SM Higgs Sensitivity

• New Higgs sensitivity study from CDF DØ in
  2003

Per Jonsson - Imperial College London
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Major Improvements

• 6x more lumi (2 fb-1 ) 2.4
• We need both CDF and D0 1.4
• Multivariate analysis 1.7
• NN b-tagging 1.35
• Di-jet mass resolution 1.2
• Additional search channels 1.15