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Higgs Reach Through VBF with ATLAS

Higgs Reach Through VBF with ATLAS. Recontres de Moriond 2004 QCD and High Energy Hadronic Interactions. Bruce Mellado University of Wisconsin-Madison. Outline. Introduction Higgs Discovery Potential SM Higgs Low Mass SM Higgs Intermediate Mass SM Higgs Overall ATLAS potential

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Higgs Reach Through VBF with ATLAS

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  1. Higgs Reach Through VBF with ATLAS Recontres de Moriond 2004 QCD and High Energy Hadronic Interactions Bruce Mellado University of Wisconsin-Madison

  2. Outline • Introduction • Higgs Discovery Potential • SM Higgs • Low Mass SM Higgs • Intermediate Mass SM Higgs • Overall ATLAS potential • MSSM Higgs • Prospects of Couplings Measurement • Conclusions Bruce Mellado, Moriond 2004, 02/04/04

  3. VBF gg  H Associated SM Higgs at LHC • Production: • Direct • gg  H • Dominant • Large background at masses close to LEP limit • qq qqH (VBF) • Distinct final state • Associated • ttH, WH, ZH • Small cross-section Bruce Mellado, Moriond 2004, 02/04/04

  4. Jet Jet Forward jets f h Higgs Decay Low Mass Higgs via VBF • Wisconsin Phenomenology Institute (D.Rainwater, D.Zeppenfeld et al.): • Two high PT jets with large Dhseparation • Strong discovery potential for low Higgs mass • Helps measuring couplings • Feasibility studies • CMS Note 2003/033 • ATLAS SN-ATLAS-2003-024 • Updates in progress Bruce Mellado, Moriond 2004, 02/04/04

  5. Major Experimental Issues • Major experimental issues addressed with a full detector simulation (Geant3) • Tagging forward jets: • Efficiencies critical • Full simulation used • Double tag efficiency ~50% • Central jet veto: • Pile up effects introduce fake central jets • Effect small at low luminosity • Serious concern at high luminosity • Currently ATLAS is assessing feasibility of entire analysis with a full detector simulation Bruce Mellado, Moriond 2004, 02/04/04

  6. Low Mass Higgs via VBF • H->WW*->ll,lqq. Strongest in 125<MH<190 GeV • Main background: • tt EW WWjj • W + 4 jets • H->->ll,lh (+ptmiss). Strong around LEP limit • Main background • QCD and EW Zjj • H->. Contributes around LEP limit • Main background • Real and fake non-resonant  Bruce Mellado, Moriond 2004, 02/04/04

  7. H->WW*->ll • Two neutrinos in final state. No narrow mass peak, transverse mass is used, instead • May achieve large signal-to-background ratio • Background: tt, EW WWjj • Understanding of tt production is crucial • Background suppression: • Well separated forward jets and central jet veto • b-jet veto • Lepton angular correlations ATLAS Preliminary Used MC@NLO for tt production Bruce Mellado, Moriond 2004, 02/04/04

  8. Perturbative QCD Parton Shower H->WW*->ll(cont) • ATLAS updated study with new simulation of tt • Old study based on Pythia • New study based on MC@NLO/HERWIG • Strong differences between generators • PT of tt and jet multiplicity • However, discovery potential does not suffer significantly • Made mass dependent cut optimization Bruce Mellado, Moriond 2004, 02/04/04

  9. H->WW*->ll(cont) • Evidence of Spin-0 resonance in H->WW->ll modes • Look into difference in  between leptons Signal Region Outside Signal Region MT<175 GeV MT>175 GeV Bruce Mellado, Moriond 2004, 02/04/04

  10. H-> Collinear approximation • H analyses (->ll,lh): • M reconstruction using collinear approximation (mass resolution ~10%) • Missing ET and  reconstruction, critical issues • Background (Zjj) rejection • Well separated forward jets and central jet veto H-> ->ll 30 fb-1 CMS ATLAS Bruce Mellado, Moriond 2004, 02/04/04

  11. Fake Real H-> • Narrow peak with ~1.4% mass resolution • Backgrounds • Real and fake photons • Suppression • Well separated forward jets and central jet veto • Diminished by large fake photon contribution • ~2 for 30 fb-1 • Needs more work ATLAS Bruce Mellado, Moriond 2004, 02/04/04

  12. Intermediate Mass Higgs via VBF • Used for first time HWWll and HZZllqq associated with two hard jets for intermediate masses (2MZ<MH<500 GeV) • By using kinematic fits obtain (M/M2.5%) with HZZllqq • Discovery confirmation and direct measurement of couplings ratio ATLAS Preliminary Bruce Mellado, Moriond 2004, 02/04/04

  13. Sensitivity to low mass SM Higgs dominated by VBF • VBF studies extended to intermediate masses ATLAS Preliminary Bruce Mellado, Moriond 2004, 02/04/04

  14. H->WW->ll Multivariate Analysis • Signal significance improvement with neural network based analysis: • Neural network output used as a discriminating variable with likelihood techniques • NN applied to H->WW->ll and H->->ll • Similar results • Results improve by 45-50% • 5 effect for MH>115 GeV with one exp and 10 fb-1 providednominal detector performance ATLAS Bruce Mellado, Moriond 2004, 02/04/04

  15. MSSM Higgs Discovery Potential One Experiment 10 fb-1 (With VBF) Two Experiments 10 fb-1 (No VBF) Bruce Mellado, Moriond 2004, 02/04/04

  16. Couplings Measurement • ATLAS attempted a global fit to cross-sections of known channels to extract Higgs couplings • Higgs searches associated with two hard jets play a big role Bruce Mellado, Moriond 2004, 02/04/04

  17. Couplings Measurement (cont) Relative Couplings Relative Branching Ratios Bruce Mellado, Moriond 2004, 02/04/04

  18. Summary • Searches associated with two hard jets dominate sensitivity for low mass Higgs • Forward jet tagging efficiency crucial and understanding of central jet veto - crucial issues • With Neural nets and likelihood techniques may reach 5 effect for MH>115 GeV with one experiment and 10 fb-1 assuming expected detector performance • ATLAS has extended these searches to 2MZ<MH<500 GeV • With these searches one experiment may cover all MSSM parameter space with 10 fb-1 • Efforts underway to address entire analysis with a full detector simulation wit systematic error studies with “data-like” control samples • SM Higgs Coupling measurements (low mass): • Accuracy of relative branching ratios and relative couplings vary from 10% to 60% depending on coupling and mass Bruce Mellado, Moriond 2004, 02/04/04

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