# Presentation: 118077

## 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 to Higgs mass

- SM: We know where to look

- SUSY Higgs looks interesting

- SM LEP Direct search: mH > 114GeV
- SM indirect constraint:  mH < 154GeV

## Colliders and Experiments

- Tevatron: 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

## Tools: Triggers and Leptons

- Higgs decays to heavy particles
- Extract handful of Higgs events from a background 11 orders of magnitudes larger

- Primary triggers: High pTe and 
- Jet+MET triggers: modes with no charged leptons, supplement lepton triggers for gaps in coverage
- Dedicated  triggers:
- 	track+MET+Cal Energy
- Lepton Id
- Optimize lepton Id on large samples of W, Z bosons

- Maximizing Higgs acceptance

## Tools: b quark jets

- b 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

- Improvements in jet energy(dijet mass) resolution
- Jet energy measurement combining calorimeter and tracking information
- NN based jet energy corrections

- DØ: NN tagger

- CDF SV tagger

## Tools: Backgrounds

- SM processes create a variety backgrounds to Higgs detection
- 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

- B factory searches
- B, Invisible light Higgs: A0
- H+, dark matter implications

## BSM Higgs: bb

- BSM Higgs: bb

- CDF and DØ 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 using multiple operating points
- Simulation/data driven studies of background
- No Evidence for Higgs:
- Limits tan vs mA
- 3b search very sensitive with certain
- 	SUSY parameter choices

## BSM Higgs: 

- BSM Higgs: 

- CDF and DØ  channel
-  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

- DØ: bb

- DØ: 

- CDF: 

## Other BSM Higgs Searches

- DØ: H benchmarked as SM search
- Fermiophobic Higgs
- At lower mass large BR(H) ~10%
- Key issue: understanding QCD background: uses excellent calorimeter

- WHWWW (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

- 2.6
- signal

## High mass: HWWll decay available
Take advantage of large ggH production cross section
Low Mass: Hbb, QCD bb background overwhelming 
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, QCD bb background overwhelming
- 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

##  SM Higgs: ZHllbb 

-  SM Higgs: ZHllbb

- ZHllbb - 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 analysis
- 					DØ : 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

##  SM Higgs: VHMETbb 

-  SM Higgs: VHMETbb

- ZHbb, WHlbb(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 background
- Shape 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 combining
- 	tracking and calorimeter information
- 	3 jet events including W acceptance
- DØ also performs a dedicated W

##  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 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

## Other SM Higgs Searches

- CDF and DØ are performing 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 benchmark for LHC
- DØ: H 
- Also model independent and fermiophobic search
- DØ: WHbb, new mode
- Dedicated search with hadronic  decays
- DØ: ttH, new mode

| Analysis: Limits at 160 and 115GeV | Exp. Limit | obs. Limit |
| --- | --- | --- |
| CDF WHWWW | 33 | 31 |
| DØ WHWWW | 20 | 26 |
| CDF VHqqbb | 37 | 37 |
| CDF H | 25 | 31 |
| DØ WHbb | 42 | 35 |
| DØ H | 23 | 31 |
| DØ ttH | 45 | 64 |

##  SM Higgs: HWW 

- HWWll - 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

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

## SM Higgs: HWW 

- SM Higgs: HWW

- 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 experiments
- Approaching
- SM sensitivity!

## SM Higgs Combined Limits

- Limits 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 channels
- Expected sensitivity of CDF/DØ combined: <3.0xSM @ 115GeV

## SM Higgs Combination

- High mass only

- Exp. 1.2 @ 165, 1.4 @ 170 GeV

- Obs. 1.0 @ 170 GeV

## SM Higgs Combination

- Result 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

## LHC Prospects: SM Higgs

- ATLAS preliminary

- Exclusion at 95% CL

- LHC experiments have the potential to observe a SM Higgs at 5 over a large region of mass
- Observation: ggH, VBF H,  HWWll, and HZZ4l
- Possibility of measurement in multiple channels
- Measurement of Higgs properties
- Yukawa coupling to top in ttH
- Quantum numbers in diffractive production

- CMS

- All key channels
-  explored

## LHC Prospects: BSM Higgs

- Strong 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

## 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 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 SM Higgs boson and study it’s properties.

## Projections

- SM Higgs Excluded: mH = 170 GeV

- Goals for increased sensitivity achieved
- Goals 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

## Backup

## SM Higgs Combined Limits

- Limits 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 channels
- Expected sensitivity: <3.0xSM @ 115GeV

- April: hep-ex/0804.3423

## HWW Systematic Uncertainties

- HWW Systematic Uncertainties

- Shape systematic evaluated for
- Scale 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

## Higgs and top