Updated results from the top group for DPF/APS

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Updated results from the top group for DPF/APS

• April 2003
• DØ Top Group

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Summary of Updates

• Optimized Soft Muon Tag
• New leptonjets x-sec combined result
• Di-electron channel joins em and mm
• New dilepton x-sec combined result
• New combined tt x-sec

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Updated leptonjets result with Soft Lepton Tag
Analysis Nobs Bkg. Tot. Sig.
ejets 2 0.16?0.10 0.54
mjets 0 0.74?0.38 0.82
For s 7pb
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Updated ljet Cross-Section Results
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Dielectron channel

• Luminosity 48.2pb-1
• Selection
• 2 isolated electrons with track match,
  pT gt 20GeV, and h lt 1.1 (central)
• At least 2 jets, pT gt 20GeV, and h lt 2.5
• MET gt 25 GeV (40 GeV in the Z mass window)
• HT (Sum of pT of electrons and jets) gt 120 GeV

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Backgrounds

• Instrumental, fake electron or fake MET
• Z ? eejj with fake MET
• W ? enjj with a jet faking an electron
• QCD ? jjjj, with 2 jets faking electrons and
  mismeasured fake MET
• Estimated completely from data
• Physics backgrounds
• Z ? tt, and WW
• Estimated from MC.

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Comparison of data with expectations
Cut fake bkgd phys bkgd Expected signal Total expected signalbackground Observed events
ee MET 8.29 0.42 0.400.04 9.111.09 9
2 jets 1.16 0.02 0.260.02 1.440.47 4
HT 0.98 0.02 0.250.02 1.250.48 4

• Summary for the eejj channel
• expect 1 background event, 0.25 top events
• observe 4 events

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Summary of dilepton cross sections
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Summary preliminarytt cross sections