APS

1
Inclusive J/? Production at DØ
Chunhui Luo
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Outline

• D0 detector elements crucial for the J/? cross
  section measurement
• Summary of Run I Results
• J/ ? signal in Run II
• Cross Section Determination
• Future Polarization Measurement
• Aims
• Test of Quantum Chromodynamics (QCD)
• Test of the Detector performance

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The Run II DØ Detector
antiprotons
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DØ Tracker
125 cm
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Muon System

• Central and Forward regions, coverage up to ?
  2
• Three layers one inside (A), two outside (B, C)
  the toroid magnets
• Consists of scintillators and drift tubes
• Central Proportional Drift Tubes (PDTs)
• 6624 drift cells (10.1 ? 5.5 cm) in 94 three-
  and four-deck chambers
• Central Scintillation Counters
• 360 cosmic ray counters outside the toroid (??
  22.5?)
• 630 A?? counters inside (?? 4.5?), ?? 0.1
• Forward Mini Drift Tubes (MDTs)
• 6080 8-cell tubes in 8 octants per layer on
  North and South side, cell cross-section 9.4 ?
  9.4 mm
• Forward Scintillation Counters (Pixels)
• 4214 counters on the North and South side
• ?? 4.5? matches the MDT sector size

Fully commissioned
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Muon System Performance
Matching of central tracks to ?s improves
momentum resolution
J/? invariant mass
Muon stand alone system
Muon plus central tracking
CHEP02 31st International Conference on High
Energy Physics, Amsterdam, 24 31 July, 2002
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DØs First J/? Candidates

• 5 pb-1
• J/???? vertex
• pT(track)gt2 GeV/c, matched to a muon
• Positive decay length

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Run I J/? production cross section
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Run II J/? production cross section
N(J/?)
s(J/?)
L ekine eaccept etrigger ereco etrack-match
L Luminosity 4.8 pb-1
eaccept inactive material, etc.
ekine only simulate muons which reach muon
chamber
etrigger di-muon trigger.
ereco muon system only
etrack-match muons matched to central track
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Run II J/? production cross section
4.8 pb-1 of data

30 systematic uncertainty
region not measured in Run I
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Jpsi Signal

• By January 2003, 129K J/? s are collected
• Integrated Luminosity
• 50 Pb-1

J/? 129K Upsilon17K
s(J/?) 78 3 MeV
N(J/?) 129,024
Invariant Mass (GeV)
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Future measurements J/? polarization
? angle(J/?lab,µJ/?) I(?) 3/2/(a3)
(1 a cos2 ?)
MC
a (sT -2sL)/(sT 2sL)
This distribution is Monte template to use to
find J/ ? polarization.
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Conclusion

• First measurement in the new kinematic range.
• Rapidity Range 0.0-1.8
• Energy of Central Mass 1.98 TeV
• Consistent with Run I measurement
• Near Future
• Cross Section measurement using full statistics
  and improved reconstruction software for Jpsi
  and upsilon states
• Reconstruct ?c -gt J/? ? decay
• J/?, upsilon Polarization measurement will be
  measured