Reconstruction of B-hadron final states at D

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Reconstruction of B-hadron final states at DØ

• Paul Balm
• April 21, 2002
• APS April Meeting

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B-physics at DØ in Run II

• Run II of the Tevatron has started March 2001
• Detector improvements in Run II, e.g
• Superconducting 2T solenoid installed, new
  Silicon detector and Fiber Tracker
• Tracking out to h 3, muon coverage to h
  2
• Tevatron upgrade
• Beam energy increase from 1.8 to 2.0 TeV, yields
  20 increased bb production cross-section
• Expected integrated luminosity Run IIa 2 fb-1
• (factor 20 increase from Run I)
• Much increased B-physics potential!

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pT resolution of tracker
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Measurement of sin(2?)

• Measure lifetime of Bd-mesons decaying to J/?Ks
  and tag flavour (Bd or Bd)
• For ease of triggering Require J/? decay to two
  leptons, Ks to charged pions

?
?
?
J/????
?-
Ks
Bd
p
p
B meson
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J/? reconstruction

• J/? in muon system
• Currently track-quality cuts only, 70 eff.
• Can use opening angle, scintillator timing, to
  improve S/B

• muon system only tracks
• pT gt 3 GeV, tight quality
• Fit result
• M(J/?) 3.08 0.04 GeV
• width 0.78 GeV

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J/? reconstruction

• J/? in the trackers
• (awaiting approval)

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Ks reconstruction

• Ks from Bd decays low pT
• but Ks average decay
• length is 5.8 cm
• cut on
• transverse decay length
• vertex ?2
• collinearity

B?J/?Ks MC
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Ks selection criteria
?
?
?
collinearity angle
Ks
?
Bd
p
p
B meson
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Ks mass peak

• decay lengthT gt 0.35 cm
• ??- vertex ?2 lt 15
• coll.angle lt 0.8 deg

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Expected sin(2?) resolution

• Uncertainty on sin(2 ?)
• with signal-dilution factors
• Dmix due to Bd mixing
• Dbgd due to background events
• (?D2)tag is the tagging efficiency
• Nrec (20k exp. in 2 fb-1) the number of
  reconstructed events
• DÆ expects (?D2)tag of 9.8 and S/B of 0.75 Þ
• expect sin(2?) resolution of 0.04 (sys)

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Flavour tagging
Tag (?D2) measured CDF Run I (?D2) expected CDF Run II (?D2) expected DÆ Run II relevant DÆ difference
same side 1.8 0.4 0.3 2 2 same
soft lepton 0.9 0.1 0.1 1.7 3.1 lepton coverage
jet charge 0.8 0.1 0.1 3 4.7 forward tracking
opp. side 2.4 0 no Kaon ID
combined 9.1 9.8
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Recent sin(2?) measurements

• Preliminary measurements presented at Moriond
  conference (March 2002)
• combination of many channels
• (J/yKL, KSp0p0,)
• Babar 0.79 0.09 (stat) ? 0.04 (sys)
• Belle 0.82 0.12 (stat) ? 0.05 (sys)
• DØ expects 0.04 (stat) in the channel
  J/yKSmmpp- in 2 fb-1 of data (Run IIa)

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Conclusions

• Reconstruction of J/y and Ks successful and
  improving
• On track for a competitive measurement of sin(2b)
• Plus many more B-physics measurements unique to
  the Tevatron
• see talk by Raymond Gelhaus