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On behalf of the

Higgs Searches a t Tevatron. M axim Titov, CEA Saclay , France. On behalf of the. COLLABORATIONS. 18 August 2011, Moscow, Russia. Reaching the Higgs Horizon. Introduction Challenges and Analysis strategies Standard Model Higgs Searches New Tevatron combined result

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  1. Higgs Searches at Tevatron MaximTitov, CEA Saclay, France On behalf of the COLLABORATIONS 18 August 2011, Moscow, Russia

  2. Reaching the Higgs Horizon • Introduction • Challenges and Analysis strategies • Standard Model HiggsSearches • New Tevatron combined result • Beyond Standard Model Higgs The excellent performance of the Tevatronduring last few years has sparked the realisationthat a HiggsmightbeobservedatTevatron, thusensuring acomplimentarity of Tevatronand LHC Searches

  3. Exciting interplay of Higgs physics and direct supersymmetrysearches Self-consistency of the SM and Higgs Boson A light Standard Model Higgs hypothesis is in agreement with all indirect tests Indirect constraints • Precision electroweak observables are sensitive to the Higgs boson mass via quantum corrections. mH< 161 GeV (95% CL)

  4. The absence of a light Higgs implies New Physics beyond SM First the Higgs Boson has to bediscovered !!! Is it a Standard Model or MSSM Higgs...? Mass: determines SM Higgsprofile Width/partial width/ couplings Spin and CP quantum numbers Higgs self-coupling Tevatron/ LHC LHC/ sLHC/ Linear Collider Higgs is a journey, not a destination

  5. Run I Run IIa Run IIb Bunches in Turn 6  6 36  36 36  36 s (TeV) 1.8 1.96 1.96 Typical L (cm-2s-1) 1.6 1030 1x1032 4.0 1032  Ldt (pb-1/week) 3 15-20 50-60 Bunch crossing (ns) 3500 396 396 # int./ crossing 2.5 2.5 7.0 Tevatron Accelerator World’s highest energy proton-antiproton collider

  6. Tevatron: Run II IntegratedLuminosity Results today using up to 8.5 fb-1 Expect > 10 fb-1analyzabledata by end of September 2011

  7. Tevatron Experiments: CDF & D0 • Two general purpose detectors: • Central tracking system embedded • in a solenoidal magnetic field: • Silicon vertex detector • Tracking chamber (CDF) • Fiber tracker (DØ) • Preshowers • Electromagnetic and hadronic calorimeters • Muon system Rapidity coverage: CDF Dzero Tracking2.0 2.5 Calorimeter 3.6 4.0 Muon 1.0 2.0 B-field 1.4 T 2.0 T

  8. SM Higgs Boson Production at Tevatron • Main production mechanisms (115<mH<180 GeV): • Gluon fusion (gg  H): ~0.8-0.2 pb • Associated production (VH, V=W,Z): ~0.2-0.02 pb • Vector boson fusion (VBF): ~0.1-0.02 pbs

  9. SM Higgs Decays and Search Strategy at Tevatron mH < 135 GeV: VH (V=W,Z) production with H→bb decay mH > 135 GeV: gg→H production with H→WW→lnln decay • Analyze all decay channels to • achieve the best sensitivity (e.g.): • Direct: gg H  tt, gg • VBF: qqH  qqbb, qqH qqWW • ttH  l+jets, ttH  all jets •  Combine all CDF/DO channels ~ 400 -700 Higgs events produced with 10 fb-1

  10. Backgrounds to SM Higgs Production • QCD Multijets(data driven methods) •  Jets faking leptons, ETmiss from mismeasured jets • Z/g + jets (ALPGEN/PYTHIA, NNLO theory cross-section, data-based corrections to model pT(Z)) •  mismeasuredjets or leptons yielding MET • W+jets, W+g (ALPGEN/PYTHIA, NNLO theory cross-section, data-based corrections to model pT(W) and/or data drivenmethods) • jets or g faking lepton • Diboson - WW, WZ, ZZ (PYTHIA, normalized to NLO cross-section; NLO correction for pT and di-lepton opening angle) • ttbar, single top (ALPGEN/PYTHIA, COMPHEP; normalized to NNLO)

  11. Main Low Mass Higgs Channels • gg H  bb • final state overhelmed by QCD • Main channel: associated • production WH / ZH with H→bb • Extremely challenging (requires • Excellent b-tagging, dijet mass • resolution, bkgds understanding) ZHl l bb WH  lnbb ZHnnbb WH→lnbb: lepton+MET+2 b-jets  Largest signal rate  Larger V+jets background • ZH→lnbb: MET+2 b-jets •  Comparable signal rate to WH • (+WH→lnbb with missing lepton) • Challenging instrumental • background ZH→llbb: dilepton+2 b-jets Smallest Higgs signal rate  Low background  Kinematicallyconstrained

  12. Searching for VH (H  bb) Step 1: Identify events consistent with leptonic W/Z decays and >= 2 jets • Trigger on high pT electrons, muonsor ETmiss • Wln: e or m and high ETmiss • Zll: ee or mm consistent with Z resonance • Znn: no charged leptons; high Etmissand 2 acoplanar jets

  13. b-Jet Identification and Tagging Step 2: b-tagging (reduces backgrounds by two orders of magnitude) • B-tagging exploits information on: • Lifetime: displaced tracks and/or vetices • Mass: secondary vertex mass • Soft leptons • Use MVA for improved performance: •  NN for b-to-c discrimination after secondary vertex tagging; •  NN for b-to-light: continuous tagger(multiple operating points) b-jet eff. ~ 50% mis-tag rate ~ 0.5% e.g. DO: NIMA620 490-517 (2010) Before b-tagging =1 tightb-tag ≥2 looseb-tags S:B ~ 1:4000 S:B ~ 1:400 S:B ~ 1:75 13 13 13

  14. VH (H  bb): Control Regions Step 3: Validate background modelling in control regions Multijetenhanced: looseningmissingETmiss (and related variables) Top enhanced: require isolated lepton and two 2b-tag jets W+jets enhanced: require isolated lepton Similar control regions for other final states and heavy flavourenhanced samples

  15. Dijet Mass Resolution • The invariant mass of the bb pair is the most sensitive variable to the Higgs • An improvement in resolution has a direct impact on the search sensitivity Exploit information from tracker, preshower, jet shape variables, semileptonic b-decays with the NN  15% resolution improvement How to choose 2jets from 3jets or more?Instead of using two largest pT jets, use two most b-like jets from bID information. S/B remainssmall, needadvanced (multivariate) analysis techniques

  16. Multivariate Analysis Techniques Step 4: Optimize separation via multivariate technique • Exploit information from severaldiscriminantvariablesand their correlations • Improves sensitivity compared to cut-based analysis by ~15-20% • However, must be very careful with the choice of training sample • Many checks performed in different kinematic regions to validate • the modeling of the inputs to the MVA method and its output; • Same optimization/techniques in similar • final states as for Higgs searches: • Single top • Dibosonhadronicdecays

  17. DibosonHadronicdecays: Validation of Search Techniques WZ+ZZnnbb,nncc: VS D0 NOTE-6223 (2011) • For mH=115 GeV • WH→lbb: σ = 26 fb • ZH→bb: σ = 15 fb • ZH→llbb: σ = 5 fb • Total VH: σ = 46 fb • Replace Z with H • WZ→lbb: σ = 105 fb • ZZ→bb: σ = 81 fb • ZZ→llbb: σ = 27 fb • Total VZ: σ = 213 fb 17 17 17

  18. Interpreting the Data: Limit Plots • Use the final discriminant distribution (e.g. NN output) to perform • hypothesis testing (S+B vs B-only) • In the absence of excess, set limits using: •  A Bayesian method (flat prior signal, credibility intervals) •  The CLS method (log-likelihood test statistic CLS = CLS +B /CLB) Upper cross section limit for Higgs production relative to SM prediction Observedlimit (solid line) from data Expectedlimit(dot dashed line) and predicted1σ/2σ (green/yellow bands) variations from background onlypseudo-experiments

  19. VH (H  bb): Low Mass HiggsSearches ZHllbb WHlvbb VHvvbb (7.9fb-1) (7.5fb-1 ) (7.8fb-1) CDF NOTE-10593 (2011) CDF NOTE-10583 (2009) CDF NOTE-10596 (2011) CDF NOTE-10572 (2011) Exp(obs) - 3.9(4.8) x SM @ MH=115 GeV Exp(obs) – 2.7 (2.6) x SM @ MH=115 GeV Exp(obs) – 2.9 (2.3) x SM @ MH=115 GeV

  20. VH (H  bb): Low Mass HiggsSearches ZHllbb WHlvbb VHvvbb (8.6fb-1) (8.5fb-1 ) (8.4fb-1) D0 NOTE-6223 (2011) D0 NOTE-6166 (2011) D0 NOTE-6220 (2011) Exp(obs) – 4.8(4.9) x SM @ MH=115 GeV Exp(obs) – 3.5(4.6) x SM @ MH=115 GeV Exp(obs) – 4.0 (3.2) x SM @ MH=115 GeV

  21. Low Mass Higgs Searches: Summary 95% CL Limits at mH = 115 GeV: Tevatron Combination H  gg: D0: arXiv: 1107.4960

  22. Searches for High Mass Higgs Dominant decay mode for mH> 135 GeV: H WW Clean environmentcantake advantage of gg → H production: • 2 opposite charge highpT leptons • Missing ET (E Tmiss) Signal contribution alsofromassociated production (W/Z+H) and VBF (qqH): ~ 35 % more signal  Consider all final states with 2 high-pT leptons and ETmiss

  23. H  WW  lnln: Analysis Strategy Step 1: Preselect events with two isolated high-pTleptons • Split analysisaccording to: • D0: Lepton flavor: ee, em, mm • CDF: Signal purity based on lepton quality • CDF: Low (<16 GeV) di-lepton mass •  Different instrumental/fake backgrounds • Different background compositions Suppress the dominant Z/g background:  Use kinematics, in particular ETmiss based variables that ensure ETmiss is significant and not due to mis-measured object.  DO (ee, mm) employs Decision Trees trained against Z/g

  24. H  WW  lnln: Control Regions Step 2: Validation of background modelling and search techniques that share characteristics of the signal Diboson cross section measurements: W+jets : same-sign dileptons CDF NOTE-9753 (2009) Define control regions to test modelling for different backgrounds: t-tbar : opposite- sign dileptons, >= 2 jets, b-tag CDF NOTE-10358 (2010)

  25. H  WW  lnln: Final Discrimination Step 3: Multivariate analysis • Split analysis according to jet multiplicity: • better sensitivity to H+jets final states: qqH, WH, ZH (important for low mass) • Each multiplicity bin correspond to • a different dominant background: • 0 jet: WW • 1 jet: WW; Z/g • ≥2 jets: ttbar 2-jet 1-jet MVA optimized for each channel & mass hypothesis. Input MVA variables (e.g. D0): mH = 165 GeV 0-jet D0 NOTE-6219 (2011) CDF NOTE-10599 (2011)

  26. VH  V W+W-  l+l+ + X Additional sensitivity ( ~ 10%) from same charge dileptonselection • Main backgrounds are instrumental: • Lepton charge mis-ID (Z/g*l+l-) • Jets faking leptons (multijet, W+jet/g) Final multivariate (BDT, NN) discriminants to analyzedata Exploit: Event topology, lepton kinematics, jet content, relation between lepton and ETmiss … W/Z W/Z D0: arXiv 1107.1268(2011) CDF NOTE-10599 (2011)

  27. SystematicUncertainties: H  WW • Data consistent with the background-only hypothesis within the systematic uncertainties. • Significant sensitivity at high mass!

  28. TevatronCombination: July 2011 CDF Combination: D0 Combination: D0 NOTE-6229 (2011) Tevatron(CDF + D0) Combination: S+B versus B-onlyHypotheses (LLR = -2lnQ, where Q = Ls+b/Lb) Most “signal-like’ excess consistent with Higgs of 130 GeVbut also consistent with background-only hypothesis

  29. TevatronCombination: July 2011 Tevatron Combination: mHLimit/ SM (GeV)OBS. EXP. 115 1.22 1.17 130 2.02 1.37 165 0.48 0.58 180 1.17 1.98 Observed limit (data) July 2011 Tevatron Combination: arXiv:1107.5518 SM Higgs excluded @ 95 % CL: Observed Exclusion: 100 < mH < 108 and 156 < mH <177 GeV Expected Exclusion: 100 < mH < 109 and 148 < mH < 180 GeV

  30. TevatronProjections and Prospects • Including ongoing analysis • improvements and more • channels: • Exclusion potential for • mH < 190 GeV • 2-3 s sensitivity for • mH ~ 115-130 GeV • Best current limit for mH<130 GeV • Unique window into H bb • H WW analysis sensitive to • different signals and backgrounds than LHC around 130-140 GeV 1-3 * SM

  31. Beyond the Standard Model Higgs

  32. Higgs Sector in MSSM • MSSM requires exactly 2 Higgs doublets: • one couples to up-type quarks (vev vu) • another couples to down-type quarks (vev vd) • Important parameter: tan b = vu/vd • tan b ~ 35 = mt/mb is appealing (large tan b) • After EW breaking: 5 physical states • ‣ 3 neutral Higgs bosons: h/H (CP-even) • and A (CP-odd) • (convention: mh < mH, h/H/A generically denoted j) • ‣ 2 charged Higgs bosons: H± • At tree level: EW breaking controlled by MA • and tanβ. Radiative corrections make it • more model dependent. • • There must be a light Higgs (h): mh ≤ 135 GeV H/A/H+ nearly equal mass when mAlarge Higgscouplingto b-quarks enhanced by tan β  sPROD ~ tan2b

  33. Neutral MSSM Search Strategy: h/H/A Decay Modes Overwhelming QCD background • Relatively clean signature • low BR ~10% Three complimentary channels: • High BR ~90% • Large multijet background • Reduced background • Additional sensitivity at low mA

  34. BSM Higgs: b(b) + F0 bbb(b) • Both CDF and DØ see ~2s excesses around mA~120-150 GeV CDF: arXiv: 1106.4782 (2011) D0: PLB698, 97 (2011)

  35. BSM Higgs: b(b) + F0 tt and bF  b tt • Tevatron searches does not observe any significant excess ftt arXiv: 1106.4555 (2011) D0 Note 6227 (2011) bfbtt

  36. Summary & Outlook • CDF and D0 have paved the way and brought sophistication and maturity into Higgs boson searchesat hadron colliders. • Tevatron is on track to deliver Higgs search results in spring 2012 based on the full 10 fb-1 datasets with promised sensitivity goals NATURE WILL, IN ALL LIKELIHOOD, SURPRISE US !

  37. Back-Up Slides

  38. What Would a Higgs Signal Look Like Signal Injection Test (6 fb-1): Tevatron Observed Limit: • Consider main low mass analyses (WHlnbb, ZHnnbb, ZHllbb) at 6 fb-1 and evaluate expected LLR after injecting a SM-like signal at mH=115 GeV •  observed limit consistent with a what would be expected from signal+background (but also consistent with background-only) A. Juste, 2011 DPF Meeting, August 2011

  39. ATLAS and CMS Combinations

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