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

Outline Introduction Triggers Analyses: Conclusion, Prospects tt  all hadrons tt  electron + jets Conclusion, Prospects NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

Physics motivation X-sec: Mass: Top physics QCD HQ production Mtop provides restriction on Mhiggs Top physics spin correlations Vtb DØ Run 1 Mtop DØ Run 2 Mtop NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

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 NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

Event topology  e 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 jet e+jets:4 jets + e + νe b-jet jet b-jet e jet  jet b-jet Hadronic: 6 jets jet b-jet jet NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

Triggers Hadronic channel: Electron + jets channel: focus on jet multiplicity, high total transverse energy (= HT) Electron + jets channel: focus on electron identification + jet multiplicity tt  e+jets tt hadronic Signal Efficiency Background Trigger Rate Background Trigger Rate Simulated BG Trigger Rate L1 99 % 88 Hz 100 % 36 Hz 47.8 Hz (only pT > 20 QCD MC) L2 95 % 52 Hz 99.0 % 8 Hz 4.1 Hz L3 75 % 6 Hz 97.8 % 1.4 Hz NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

(L. Phaf, I. Iashvili et al.) 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. NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

tt  e + jets candidate passes Run I cuts 4 reconstructed jets above Isolated electron 4 reconstructed jets above 15 GeV HT = 191 GeV Aplanarity = 0.11 η φ NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

Offline event selection event-shape variables NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

tt  e + jets candidate passes Run I cuts 4 reconstructed jets above Isolated electron 4 reconstructed jets above 15 GeV HT = 191 GeV Aplanarity = 0.11 Mtop (χ2 fit) = 165 GeV η φ NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

tt  e + jets candidate NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

tt  hadrons After selection signal/bg ~1/30 (MC signal eff ~ 44 %) (F.Blekman,M.Vreeswijk,G.Massaro) HT > 225 GeV Aplanarity > 0.05 N jets > 5 Centrality > 0.6 After selection signal/bg ~1/30 (MC signal eff ~ 44 %) Centrality = HT/H Aplanarity Jet multiplicity HT = total hadronic sum Data Lum: 2 pb-1 QCD MC Pythia, pT > 80 tt MC Pythia,hadronic tt Mtop = 174 GeV NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

tt  hadrons candidate event y x ET scale: 59 GeV -2 2 +z E scale: 51 GeV 180 eta 3.7 0.0 -3.7 -1.2 1.2 phi 2PI ET G eV 40 6 jets Passes selection cuts Secondary vertices tagged Mtop (χ2 fit) = 168 GeV φ η NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

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…. Secondary vertex probability DØ Run 2 Preliminary DØ Run 2 Data tt hadronic MC QCD MC Cuts tt  hadrons efficiency S/B ratio Selection (this study) 44 % 1/30 2 vertex tags + non-leading jet cut 25 % 1/2 ANN output NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

Prospects Expect to have 50 pb-1 reconstructed data by February 2003 Lepton + jet , di-lepton: For now: Use Analysis similar to Run 1 (based on event topology) All hadronic: Make use of improved b-tagging tt decay channel Signal events DØ Run 1 ‘Expected’ signal by spring 2003 Lepton+lepton 6 1 - 5 Lepton+jet 20 5 - 27 Hadronic 13 7 - 40 110 pb-1 @ 1.8 TeV 50 pb-1 @ 1.96 TeV, σ = 6 pb (expected eff 5 - 30 %) NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

! 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… ! NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

Event Selection event-shape variables ( hadronic channel) ttbar QCD Sphericity Sphericity Aplanarity ttbar QCD data Thrust Oblateness NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam