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NIKHEF / Universiteit van Amsterdam

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Presentation on theme: "NIKHEF / Universiteit van Amsterdam"— Presentation transcript:

1 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

2 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

3 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

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

5 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

6 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

7 (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

8 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

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

10 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

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

12 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

13 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

14 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

15 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 TeV TeV, σ = 6 pb (expected eff %) NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 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… ! NIKHEF Annual Scientific Meeting Amsterdam, December 19th, 2002 Freya Blekman NIKHEF/ Universiteit van Amsterdam

17 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

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