# Presentation: 118076

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

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

**...**

## Searches for the Higgs Boson

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

## 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

## Electroweak Constraints

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

- We know where to look

- SUSY Higgs looks interesting

- SM LEP Direct search: mH > 114GeV
- SM indirect constraint:  mH < 160GeV

## Colliders and Experiments

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

- Tevatron: SM Higgs mass exclusion 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 Higgs discovery in dedicated B physics experiments
- Babar, Belle, LHCB

- Tevatron results in this talk

## 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
- Jet+MET triggers: modes with no charged leptons
- CDF: Jet+MET triggers: supplement lepton triggers for gaps in coverage
- Dedicated  triggers:
- 	track+MET+Cal Energy

## 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

## 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

## 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, W+b, W+c, Z+b
- 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

## 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

- 0 = h/H/A

- Observable at Tevatron or LHC

## BSM Higgs: bb

- 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

## 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

## 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

- WHWWW (also SM), charged Higgs, decays to and from top...

## 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 (MET+bb), ZHllbb
Also: VBF Production, VHqqbb, H(with 2jets), H, WH->WWW, ttH

- 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 (MET+bb), ZHllbb
- Also: VBF Production, VHqqbb, H(with 2jets), H, WH->WWW, ttH

- SM Higgs Production and Decay

## Where’s the Beef Higgs

- Macroscopic Higgs Event Counts

## 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

| 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 |

- Results at mH = 115GeV: 95%CL Limits/SM

## SM Higgs: VHMETbb 

- 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

| 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

## SM Higgs: WHlbb 

- WHlbb - signature: high pT lepton, MET and b jets
- Backgrounds: W+bb, W+qq(mistagged), single top, Non W(QCD)
- Key issue: estimating W+bb 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

| 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 | 8.3 | 5.6 | 5.7 |
| DØ NN | 2.X | XX | XX | XX |
| DØ WHbb | 2.X | XX | XX | XX |

- Results at mH = 115GeV

## 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

| Analysis | Lum (fb-1) | Higgs Events | Exp. Limit | Obs. Limit |
| --- | --- | --- | --- | --- |
| CDF ME+NN | 3.0 | 16.6 | 1.8 | 1.7 |
| DØ ME+NN | 2.X | XXX | 2.3 | 2.3 |

- Results at mH = 160GeV

- Spin correlation: Charged leptons
-  go in the same direction

## 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 it’s 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 |

## 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

## SM Higgs Combination

- 2.X@115GeV

- 0.X@160GeV

## LHC Prospects

- Three LHC slides
- Will design them based on the parallel session
- Emphasis not placed on HWWll

## 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 it’s 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!