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

1. g g s … Searches for the Higgs Boson Matthew Herndon, University of Wisconsin Madison 34th International Conference on High Energy Physics

2. Searches for the Higgs Boson • Introduction • Tools of the Trade • BSM Higgs Searches • SM Higgs Searches • LHC Potential • Conclusions

3. 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

4. Electroweak Constraints • Higgs couples strongly to massive particles • Introduces corrections to W and top masses - sensitivity to Higgs mass SM LEP Direct search: mH > 114GeV SM indirect constraint: mH < 154GeV SM: We know where to look SUSY Higgs looks interesting

5. Colliders and Experiments • 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: 2TeV pp collider - general purpose detectors: CDF, DØ LHC: 14TeV pp collider - general purpose detectors: ATLAS, CMS Tevatron results in this talk Given a SM Higgs Tevatron: Higgs mass exclusions and perhaps evidence LHC: Observation over full mass range. Study Higgs properties

6. Tools: Triggers and Leptons b, H _ l b, W  H l W 1  0.03-0.3 Higgs ggH • 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

7. Tools: b quark jets “B-tag” = Identify 2nd vertex • 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 DØ: NN tagger CDF SV tagger • Improvements in jet energy(dijet mass) resolution • Jet energy measurement combining calorimeter and tracking information • NN based jet energy corrections

8. 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

9. BSM Higgs b 0 b • 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 f0 = h/H/A • B factory searches • B, Invisible light Higgs: A0 • H+, dark matter implications Observable at Tevatron or LHC

10. 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

11. BSM Higgs:  DØ: bb • 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:  CDF: 

12. 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 • Other BSM Higgs Searches • 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 2.6 signal Models: up to x10-4 BR(Y(3S)A0) < 0.7-31x10-6

13. SM Higgs Production and Decay • 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

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

15. 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: 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 Results at mH = 115GeV: 95%CL Limits/SM

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

17. 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

18. SM Higgs: HWW W+ H μ+ W+ W- ν e- W- • 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 ν

19. SM Higgs: HWW • Most sensitive Higgs search channel at the Tevatron Results at mH = 165GeV : 95%CL Limits/SM Both experiments Approaching SM sensitivity!

20. 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

21. SM Higgs Combination High mass only Exp. 1.2 @ 165, 1.4 @ 170 GeV Obs. 1.0 @ 170 GeV

22. SM Higgs Combination SM Higgs Excluded: mH = 170 GeV • We exclude at 95% C.L. the production of a SM Higgs boson of 170 GeV • Result verified using two independent methods(Bayesian/CLs) 95%CL Limits/SM

23. LHC Prospects: SM Higgs • 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 All key channels explored Exclusion at 95% CL CMS ATLAS preliminary

24. 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

25. 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 SM Higgs boson and study it’s properties. • 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

26. Projections • 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 SM Higgs Excluded: mH = 170 GeV

27. Backup

28. 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

29. 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

30. Higgs and top • Charged Higgs decays to and from top: SUSY H+