M. Herndon, ICHEP 2008 1
Searches for the Higgs Boson
Matthew Herndon, University of Wisconsin Madison
34th International Conference on High Energy Physics
g g s…
M. Herndon, ICHEP 2008 2
Searches for the Higgs Boson
IntroductionTools of the TradeBSM Higgs SearchesSM Higgs SearchesLHC PotentialConclusions
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Electroweak Symmetry BreakingConsider 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 ConstraintsHiggs couples strongly to massive particles
Introduces corrections to W and top masses - sensitivity to Higgs mass
SM: We know where to look SUSY Higgs looks interesting
SM LEP Direct search: mH > 114GeV
SM indirect constraint: mH < 154GeV
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Colliders and ExperimentsTevatron: 2TeV pp collider - general purpose detectors: CDF, DØ
LHC: 14TeV pp collider - general purpose detectors: ATLAS, CMS
Tevatron: Higgs mass exclusions and perhaps evidence
LHC: Observation over full mass range. Study Higgs properties
Excellent lepton Id
Good to excellent calorimeters for jet and MET reconstruction
Excellent silicon detectors for b jet identification
Potential for indirect and direct Higgs evidence in dedicated B physics experiments
Babar, Belle, LHCB
Tevatron results in this talk
Given a SM Higgs
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H
W
W
l
l
1
Higgs ggH 0.03-0.3
Tools: Triggers and LeptonsHiggs decays to heavy particlesExtract handful of Higgs events from a background 11 orders of magnitudes larger
Hb,
b,_
Primary triggers: High pTe and
Jet+MET triggers: modes with no charged leptons, supplement lepton triggers for gaps in coverage
Dedicated triggers: track+MET+Cal Energy
Lepton IdOptimize lepton Id on large samples of W, Z bosons
Maximizing Higgs acceptance
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Tools: b quark jetsb jet tagging
DØ: NN tagger with multiple operating points
CDF: Secondary Vertex tagger, jet probability tagger, and NN flavor separators
50-70% Efficient with 0.3-5% mistag rate
“B-tag” =Identify 2nd
vertex
Improvements in jet energy(dijet mass) resolutionJet energy measurement combining calorimeter and tracking informationNN based jet energy corrections
DØ: NN tagger
CDF SV tagger
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Tools: BackgroundsSM processes create a variety backgrounds to Higgs detection
Discovery analyses: WW, WZ, ZZ, single top, and even top pairs
Total and differential cross section measurementsQCD dijets, W+b, W+c, Z+b
Critical to HiggsConstrain 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 HiggsMany 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
b
b
0
0 = h/H/A
Observable at Tevatron or LHCB factory searches
B, Invisible light Higgs: A0H+, dark matter implications
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BSM Higgs: bbCDF and DØ 3b channel: bbbb.
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 using multiple operating points
Simulation/data driven studies of background
No Evidence for Higgs: Limits tan vs mA
3b search very sensitive with certainSUSY parameter choices
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BSM Higgs: CDF and DØ channel
pure enough for direct production search
DØ adds associated production search: bb
Key issue: understanding Id efficiencyLarge 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
DØ: bb
DØ: CDF:
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Other BSM Higgs SearchesDØ: H benchmarked as SM search
Fermiophobic Higgs
At lower mass large BR(H) ~10%
Key issue: understanding QCD background: uses excellent calorimeterOther BSM Higgs Searches
WHWWW (also SM), charged Higgs, decays to and from top…
Babar: A0, invisible light Higgs decay
Photon+Missing energy in Y(3S) decays
Key issue: e+e- background
For mA<7.8GeV
BR(Y(3S)A0 ) < 0.7-31x10-6 Models:up to x10-4
2.6signal
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High mass: HWWll decay available
Take advantage of large ggH production cross section
Low Mass: Hbb, QCD bb background overwhelming
Use associated production with W or Z for background discrimination
WHlbb, ZHbb (MET+bb), ZHllbb
Also: VBF Production, VHqqbb, H(with 2jets), H, WH->WWW, ttH
SM Higgs Production and Decay
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SM Higgs: ZHllbb ZHllbb - signature: two leptons and b jets
Primary background: 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
MET used to correct jet energies, New ME analysisDØ : Multiple advanced discriminates, NN and BDT
Analysis Lum (fb-1)
Higgs Events
Exp. Limit
Obs. Limit
CDF NN 2.4 1.8 11.8 11.6
CDF ME(120) 2.0 1.4 15.2 11.8
DØ NN,BDT 2.3 2.0 12.3 11.0
Results at mH = 115GeV: 95%CL Limits/SM
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SM Higgs: VHMETbb ZHbb, WHlbb(l not detected) - signature: MET and b jets
Primary backgrounds: QCD b jets and mistagged light quark jets
Key issue: Building a model of the QCD backgroundShape from 0 and 1 b tagged data samples with tag and mistag rates applied
Innovations:
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
Results at mH = 115GeV: 95%CL Limits/SM
CDF/DØ : Use of track missing pT to define control regions and suppress backgrounds
CDF: Uses of H1 Jet Algorithm combiningtracking and calorimeter information3 jet events including W acceptance
DØ also performs a dedicated W
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SM Higgs: WHlbb WHlbb - signature: high pT lepton, MET and b jets
Backgrounds: W+bb, W+qq(mistagged), single top, Non W(QCD)
Key issue: estimating W+bb backgroundShape from MC with normalization from data control regions
Innovations: CDF: 20% acceptance from isolated tracks, ME with NN jet corrections DØ : 20% acceptance from forward leptons, use 3 jet events
Analysis Lum (fb-1)
Higgs Events
Exp. Limit
Obs. Limit
CDF NN 2.7 8.3 5.8 5.0
CDF ME+BDT 2.7 7.8 5.6 5.7
DØ NN 1.7 7.5 8.5 9.3
Results at mH = 115GeV: 95%CL Limits/SM
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Other SM Higgs SearchesCDF and DØ are performing searches in every viable mode
CDF/DØ: WHWWW: same sign leptonsAdds sensitivity at high and middle masses Also Fermiophobic Higgs search
CDF: VHqqbb: 4 Jet mode.
CDF: H with 2jetsSimultaneous search for Higgs in VH, VBF and ggH production modesInteresting benchmark for LHC
DØ: H Also model independent and fermiophobic search
DØ: WHbb, new modeDedicated search with hadronic decays
DØ: ttH, new mode
Analysis: Limits at 160 and 115GeV
Exp. Limit
obs. Limit
CDF WHWWW 33 31
DØ WHWWW 20 26
CDF VHqqbb 37 37
CDF H 25 31
DØ WHbb 42 35
DØ H 23 31
DØ ttH 45 64
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SM Higgs: HWW HWWll - signature: Two high pT leptons and MET
Primary backgrounds: WW and top in di-lepton decay channel
Key issue: Maximizing lepton acceptance
Innovations: CDF/DØ : Inclusion of acceptance from VH(CDF) and VBF
CDF : Combination of ME and NN approaches, DØ Reoptimized NN
Hμ+
νW-
W+
e-
ν
W-
W+
Spin correlation: Charged leptons go in the same direction
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SM Higgs: HWW Most sensitive Higgs search channel at the Tevatron
Analysis Lum (fb-1)
Higgs Events
Exp. Limit
Obs. Limit
CDF ME+NN 3.0 17.2 1.6 1.6
DØ NN 3.0 15.6 1.9 2.0
Results at mH = 165GeV : 95%CL Limits/SM
Both experimentsApproaching
SM sensitivity!
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SM Higgs Combined LimitsLimits calculating and combination
Using Bayesian and CLs methodologies.
Incorporate systematic uncertainties using pseudo-experiments (shape and rate included) (correlations taken into account between experiments)
Backgrounds can be constrained in the fit
Low mass combination difficult due to ~70 channelsExpected sensitivity of CDF/DØ combined: <3.0xSM @ 115GeV
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SM Higgs CombinationHigh mass only
Exp. 1.2 @ 165, 1.4 @ 170 GeV
Obs. 1.0 @ 170 GeV
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SM Higgs CombinationResult verified using two independent methods(Bayesian/CLs)
M Higgs(GeV) 160 165 170 175
Method 1: Exp 1.3 1.2 1.4 1.7
Method 1: Obs 1.4 1.2 1.0 1.3
Method 2: Exp 1.2 1.1 1.3 1.7
Method 2: Obs 1.3 1.1 0.95 1.2
95%CL Limits/SM
SM Higgs Excluded: mH = 170 GeV
We exclude at 95% C.L. the production of a SM Higgs boson of 170 GeV
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ATLAS preliminary
Exclusion at 95% CL
LHC Prospects: SM HiggsLHC experiments have the potential to observe a SM Higgs at 5 over a large region of mass
Observation: ggH, VBF H, HWWll, and HZZ4l
Possibility of measurement in multiple channels
Measurement of Higgs properties
Yukawa coupling to top in ttH
Quantum numbers in diffractive productionCMS
All key channels explored
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LHC Prospects: BSM HiggsStrong sensitivity to a wide variety of BSM Higgs variants
Taking standard SUSY Higgs as the benchmark
Sensitive to SUSY Higgs at high and low tan
SUSY Higgs searches extended well beyond bb and modes
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Conclusions
We exclude at 95% C.L. the production of a SM Higgs boson of 170 GeV
Expect large exclusion, or evidence, with full Tevatron data set and improvements
SM Higgs Excluded: mH = 170 GeV
The Higgs boson search is in its most exciting era everThe 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 SM Higgs boson and study it’s properties.
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Projections
SM Higgs Excluded: mH = 170 GeV
Goals for increased sensitivity achievedGoals set after 2007 Lepton Photon conference
First stage target was sensitivity for possible exclusion
Second stage goals still in progress
Expect large exclusion, or evidence, with full Tevatron dataset and further improvements.
Run II Preliminary
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DiscoveryDiscovery projections: chance of 3 or 5 discovery
Two factors of 1.5 improvements examined relative to summer Lepton Photon 2007 analyses.
First 1.5 factor achieved for summer ICHEP 2008 analysis
Resulted in exclusion at mH = 150 GeV.
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SM Higgs Combined LimitsLimits calculating and combination
Using Bayesian and CLs methodologies.
Incorporate systematic uncertainties using pseudo-experiments (shape and rate included) (correlations taken into account between experiments)
Backgrounds can be constrained in the fit
Winter conferences combination
April: hep-ex/0804.3423
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HWW Systematic Uncertainties
Shape systematic evaluated forScale variations, ISR, gluon pdf, Pythia vs. NL0 kinematics, jet energy scale: for signal and backgrounds. Included in limit setting if significant.
Systematic treatment developed in collaboratively between CDF and DØ