1 / 21

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.

damien
Download Presentation

Searches for the Standard Model Higgs at the Tevatron

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related