Searches for the Higgs Boson Matthew Herndon, University of Wisconsin Madison

M. Herndon, ICHEP 2008 1

Searches for the Higgs Boson

Matthew Herndon, University of Wisconsin Madison

34th International Conference on High Energy Physics

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Searches for the Higgs Boson

IntroductionTools of the TradeBSM Higgs SearchesSM Higgs SearchesLHC PotentialConclusions


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


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


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


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


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


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


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


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


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:


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


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


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


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


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


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



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


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


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!


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


SM Higgs CombinationHigh mass only

Exp. 1.2 @ 165, 1.4 @ 170 GeV

Obs. 1.0 @ 170 GeV


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


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


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


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


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.


Backup


Projections


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


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.


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


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


Charged Higgs decays to and from top: SUSY H+

Higgs and top

Documents

Searches for the Higgs Boson Matthew Herndon, University of Wisconsin Madison