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Searches for the Standard Model Higgs at the Tevatron

Searches for the Standard Model Higgs at the Tevatron. Moriond QCD 2006 La Thuile, Aosta Valley, Italy, March 18-25, 2006. presented by Per Jonsson Imperial College London On behalf of the CDF and DØ Collaborations. Outline. Chicago .  p. p. 1.96 TeV. Booster. p. CDF. DØ.

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Searches for the Standard Model Higgs at the Tevatron

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  1. Searches for the Standard Model Higgs at the Tevatron Moriond QCD 2006 La Thuile, Aosta Valley, Italy, March 18-25, 2006 presented by Per Jonsson Imperial College London On behalf of the CDF and DØCollaborations

  2. Outline Chicago  p p 1.96 TeV Booster p CDF DØ Tevatron p p source Main Injector & Recycler Thanks to all colleagues at the Tevatron for their contributions to this talk • Introduction • Higgs  bb (low mass) • ZH bb • WH  lbb • Higgs  WW (high mass) • WH  WWW • H  WW • Limits: • combination New results! New result! New result! 36×36 bunches 396 ns bunch crossing Only new results since last year’s Moriond are shown Per Jonsson - Imperial College London

  3. Tevatron Performance 80-85% Average Efficiency • Currently in shutdown: • Silicon and Trigger upgrades 4-8 fb-1 expected by end of 2009 This talk: 261-950pb-1 Run I Per Jonsson - Imperial College London

  4. The DØ and CDF detectors • The Standard Model Higgs Boson is: • Key part of Electro-Weak symmetry breaking • A scalar with the Higgs mass as the only free parameter • DØ and CDF constrain the SM Higgs boson mass: • Indirectly: Top and W mass measurements • Directly: Search for Higgs boson production Per Jonsson - Imperial College London

  5. EW constraints on Higgs mH constrained in the Standard Model Direct searches at LEP2: mH>114.4 GeV @95%CL LEPEWWG 18/03/06 68% CL mH =89 +45 -30 GeV [GeV] [GeV] mH<175 GeV@95%CL (< 207 GeV if LEP2 limit incl.) A light Higgs is favored Per Jonsson - Imperial College London

  6. SM Higgs Production H bb H  WW(*) Dominant decay modes • Production cross sections are small: 0.1-1 pb depending on mH: ~1 in 1012 pp events is a Higgs • MH< 135 GeV: decay to bb • gg H bb overwhelmed by QCD background • searches can be performed in W/Z associated production with lower background • Best channels: • WHlbb, ZHbb • MH > 135 GeV: decay to WW • gg H WW(*)l+l- • WH WWW(*) final states can be explored We probably have a Higgs in our data already! Per Jonsson - Imperial College London

  7. Backgrounds and Tools Measurements also rely on: Jet reconstruction B-tagging: Use track impact parameter (IP) measurements or secondary vertex reconstruction Understanding and modeling of background is critical: Especially so for advanced analysis techniques Electroweak backgrounds (W, Z, WZ, WW, Top): Monte Carlo distributions normalized to (N)NLO cross sections QCD and instrumental background taken from real data control samples IP • Lepton identification • Missing transverse energy Both detectors are delivering the excellent performance needed Per Jonsson - Imperial College London

  8. Z/g*ee + jets Comparison of jet multiplicities and distributions in data and MC: Pythia 6.319 vs. Sherpa 1.0.6 Sherpa : Matrix Element + Parton showers, using CKKWalgorithm Event selection includes: Electron pT > 25 GeV, h<2.5/1.1 70 GeV < Mee < 120 GeV New result! For details see Gavin’s talk yesterday. Sherpa agrees well with data upto njet=4 L=~950 pb-1 L=~950 pb-1

  9. ZH bb Event selection includes: ≥ 1 tagged b-jets Two jets with ET > 60/25 GeV ET miss> 70 GeV Backgrounds: W/Z + heavy flavour jets QCD Di-bosons Mis-tagged b-jets Top pairs MH = 120 GeV, 80 < mjj < 120 GeV 6 events observed 4.36 +/- 1.02 predicted s95 = 4.5 pb ET1= 100.3 GeV ET2 = 54.7 GeV ETmiss = 144.8 GeV Mjj = 82.1 GeV

  10. ZH bb Improved event selection includes: Two acoplanar jets with: ET > 20 GeV ETmiss > 50 GeV Sum of scalar jet ET < 240 GeV Separate analysis for single and double b-tagged events: Increased statistics mH = 115 GeV, 75 < mjj < 125 GeV: 11 events observed 9.4 +/- 1.8 predicted s95 = 4.3 pb Same analysis for WH lnbb with missed lepton improves the WH limit New result! L=261 pb-1 L=261 pb-1 1 b-tag 2 b-tags

  11. WHlbb , (l=e,m) b jet b jet n e/m • Muon and electron channel combined: • 1 or 2 tagged b-jets • electron or muon withpT > 20 GeV • ETmiss > 20 GeV • Main backgrounds: • W + jets • Top pairs • di-bosons (WW, WZ etc.) Per Jonsson - Imperial College London

  12. WHlbb, (l=e,m) New result! • New muon analysis • Re-optimized electron analysis • Separate single and double b-tag analysis • Event selection includes: • Central isolated e/m: • pT > 20 GeV • Missing ET> 25 GeV • ≥ two jets: • ET > 20 GeV, |η| < 2.5 • One or two tagged b-jets • Limit from combined channels: • mH = 115 GeV, 85 < mjj < 140 GeV: • 6 (32 ST) events observed • 9.3 (45.1 ST) predicted • s95 = 2.4 pb Per Jonsson - Imperial College London

  13. WHWWW(*)ll qq, (l=e, Event selection includes: Two isolated like signed leptons (ee,em,mm) pT > 15 GeV ETmiss > 20 GeV s95 (mH=115 GeV) = 3.88 pb L=363 pb-1 Mainly di-bosons (WZ) CDF 194 pb-1 Per Jonsson - Imperial College London

  14. HWW(*)l+l-, (l=e, e+  W+  W- e- mH= 130 GeV • Higgs mass reconstruction not possible due to two neutrinos • Employ spin correlations to suppress the background • (ll) variable is particularly useful • Charged leptons from Higgs are collinear • Event selection includes: • Two leptons (e/) • pT > 20/10 GeV • Missing ET greater than • MH/4 • Di-lepton invariant mass • > 16 GeV • < MH/2-5 GeV • ll distribution fitted to extract 95% CL limit • SM cross section still far away, but 4th generation models getting closer mH= 160 GeV Per Jonsson - Imperial College London

  15. HWW(*)l+l- (l=e, New result! After cuts ee em • L= 950 pb-1 • ee and em channels • Event selection includes: • Isolated e/ • pT(e1, e2) > 15, 10 GeV • pT(e/1) > 15 GeV, • pT(e/2) > 10 GeV • Missing ET greater than • 20 GeV (ee, e) • Veto on • Z resonance • Energetic jets • MH = 120 GeV: • 31 events observed • 32.7 +/- 2.3 (stat) predicted • Bkg systematic uncertainty: 15% • s95 = 6.3 pb 160 GeV Higgs (x 10) Per Jonsson - Imperial College London

  16. Combined limit Currently a factor 15 away from mH =115 GeV With L= 2 fb-1, both experiments, NN b-tagging, NN analyses, track-cal jets, increased acceptance, new channels, full cross efficiency, and reduced systematics: Cross section factor = 1.2 New combined limit from all SM Higgs search channels! 14 orthogonal search channels (incl. single and double-tag analyses and WH lnbb w. missed lepton) Full account taken of systematic uncertainties High mass region benefits from HWW analyses New result!

  17. Limits

  18. Summary • The Tevatron and the experiments are performing well • A wide range of Standard Model Higgs searches have been performed by both CDF and D0 with up to 1 fb-1 RunII data: • No deviation from the SM background expectation observed • Work underway to improve sensitivity: • First combination of all channels from D0 • Very exciting prospects for the future: • Sensitivity to m H > 114 GeV starts at ~2 fb-1 • Exclusion up to 180 GeV possible with 8 fb-1 Many results already and more with increased stats are coming soon! Per Jonsson - Imperial College London

  19. Back-up slides

  20. SM Higgs Sensitivity No systematics Statistical power onlySystematics not included Improved sensitivity from refined analysis and detailed simulation The SM Higgs is a challenge, understanding of bkgs critical! • New Higgs sensitivity study from CDF + DØ in 2003: Per Jonsson - Imperial College London

  21. Major Improvements • 6x more lumi (2 fb-1 ): 2.4 • We need both CDF and D0: 1.4 • Multivariate analysis: 1.7 • NN b-tagging: 1.35 • Di-jet mass resolution: 1.2 • Additional search channels: 1.15

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