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Higgs. tracks. top. WZ. Top Physics At DØ. Top Physics At DØ. Leptons. Jets. b. DØ. Freya Blekman NIKHEF / Universiteit van Amsterdam. Outline. Introduction Triggers Analyses: tt  all hadrons tt  electron + jets Conclusion, Prospects. D Ø Run 2 M top.

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  1. Higgs tracks top WZ Top Physics At DØ Top Physics At DØ Leptons Jets b DØ Freya Blekman NIKHEF / Universiteit van Amsterdam

  2. Outline • Introduction • Triggers • Analyses: tt  all hadrons tt  electron + jets • Conclusion, Prospects Freya Blekman NIKHEF/ Universiteit van Amsterdam

  3. DØ Run 2 Mtop Physics motivation • X-sec: QCD HQ production • Mass: Mtop provides restriction on Mhiggs • Top physics • spin correlations • Vtb DØ Run 1 Mtop Freya Blekman NIKHEF/ Universiteit van Amsterdam

  4. Tevatron Top Physics • (s)=1.96 TeV • Top pair production (this talk) • Single top • t  W + b BR > 99% • tt analyses classified by W decay channels • σ(pptt)≈ 7 pb Freya Blekman NIKHEF/ Universiteit van Amsterdam

  5. Background reduction most important factor Lepton + jets: Background mainly QCD and W + jets Hadronic channel: Background mainly QCD All tt channels: 2 b-jets!  B-tagging of vital importance Event topology jet e+jets:4 jets + e + νe b-jet jet b-jet e jet  jet b-jet Hadronic: 6 jets jet b-jet jet Freya Blekman NIKHEF/ Universiteit van Amsterdam

  6. Triggers • Hadronic channel: focus on jet multiplicity, high total transverse energy (= HT) • Electron + jets channel: focus on electron identification + jet multiplicity Freya Blekman NIKHEF/ Universiteit van Amsterdam

  7. tt  e + jets (L. Phaf, I. Iashvili et al.) • Finding electrons: EM ID efficiency • High pT electrons: Count Z  e+e- with and without ID cuts ID cuts: isolation, EM fraction, pT > 20 GeV, shower shape. Freya Blekman NIKHEF/ Universiteit van Amsterdam

  8. φ η tt  e + jets candidate • passes Run I cuts • Isolated electron • 4 reconstructed jets above • 15 GeV • HT = 191 GeV • Aplanarity = 0.11 Freya Blekman NIKHEF/ Universiteit van Amsterdam

  9. Offline event selection • event-shape variables Freya Blekman NIKHEF/ Universiteit van Amsterdam

  10. φ η tt  e + jets candidate • passes Run I cuts • Isolated electron • 4 reconstructed jets above • 15 GeV • HT = 191 GeV • Aplanarity = 0.11 • Mtop (χ2 fit) = 165 GeV Freya Blekman NIKHEF/ Universiteit van Amsterdam

  11. tt  e + jets candidate Freya Blekman NIKHEF/ Universiteit van Amsterdam

  12. N jets > 5 Centrality > 0.6 HT > 225 GeV Aplanarity > 0.05 Jet multiplicity HT= total hadronic sum Centrality = HT/H Aplanarity tt  hadrons (F.Blekman,M.Vreeswijk,G.Massaro) After selection signal/bg ~1/30 (MC signal eff ~ 44 %) Data Lum: 2 pb-1 QCD MC Pythia, pT > 80 tt MC Pythia,hadronic tt Mtop = 174 GeV Freya Blekman NIKHEF/ Universiteit van Amsterdam

  13. ET scale: 59 GeV y E scale: 51 GeV x 40 +z ET G eV 2PI -3.7 -2 2 -1.2 phi 0.0 180 0 eta 1.2 0.0 3.7 tt  hadrons candidate event • 6 jets • Passes selection cuts • Secondary vertices tagged • Mtop (χ2 fit) = 168 GeV φ η Freya Blekman NIKHEF/ Universiteit van Amsterdam

  14. Secondary vertex probability DØ Run 2 Preliminary DØ Run 2 Data tt hadronic MC QCD MC Results Hadronic Channel • Efficiencies and Purities Results for preliminary study on 2 pb-1 Further study still to be done, but promising for larger dataset…. ANN output Freya Blekman NIKHEF/ Universiteit van Amsterdam

  15. Lepton + jet , di-lepton: For now: Use Analysis similar to Run 1 (based on event topology) Prospects Expect to have 50 pb-1 reconstructed data by February 2003 • All hadronic: • Make use of improved b-tagging Freya Blekman NIKHEF/ Universiteit van Amsterdam

  16. Conclusion • We see top events being produced at Tevatron • Improved b-tagging starting to make a difference • Potential measurement for the winter conferences • More interesting high pT physics to come: Stay Tuned… ! Freya Blekman NIKHEF/ Universiteit van Amsterdam

  17. Event Selection • event-shape variables ( hadronic channel) Sphericity Sphericity Aplanarity ttbar QCD data Thrust Oblateness Freya Blekman NIKHEF/ Universiteit van Amsterdam

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