Recent b physics results from OPAL

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Recent b physics results from OPAL

• David Waller, Carleton University
• for the OPAL Collaboration
• EPS Conference HEP2003
• Heavy Flavour Physics Session
• Aachen, Germany
• 17 July 2003

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Outline

• Object, motivation
• Method
• Results
• Charm counting in beauty decays
• Object, motivation
• Method
• Results
• Conclusions

Analyses of Z0 data!
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Semileptonic decay of b hadrons to orbitally
excited D mesons
Object
Motivation

• Measure
• D0 are L1 orbitally excited charm mesons.
• Measure narrow Jq 3/2 states (D10, D20).
• Wide Jq 1/2 states not visible with statistics.

• Reconcile difference between measured inclusive
  and exclusive semileptonic branching ratios.
• Reduce uncertainty in Vcb.
• Test HQET predictions.

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Semi-leptonic decay of b hadrons to orbitally
excited D mesons Method

• Identify high p lepton (?,e)
• high efficiency and purity for p?gt 3 GeV/c,
  pegt 2 GeV/c
• Exclusively reconstruct D0
• D0 D ?-
• D0 ?slow
• K-?(? ?-)
• Background cuts to remove fake ?- (? from
  fragmentation)
• main background from
• decays
• plus fake ?-
• ANN (p, pT, d0/sd0) to select ?-

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D0 D mass difference
Combine D0? K? and K3? channels to reduce
uncertainty due to background.
Unbinned ML fit to determine number of D1 and D2
events (B.-W. ? Gaussian).
Number of wrong sign and right sign background
events fit simultaneously.
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Results for
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Charm counting in b decays Object and Motivation

• Object(1) measure with
  inclusive method.
• (2) use to
  calculate average number of c plus anti-c
  quarks per b quark decay, nc.
• Motivation compare experimental value of nc to
  theoretical prediction
• nc 1.20 0.06 (Neubert Sachrajda)

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Charm counting in b decays Inclusive method

• Differentiate b?1 charm from b?2 charm using
  topology.
• Impact parameter significance, S (d0/sd0), of
  tracks from D decay greater than S of
  tracks from b decay.
• In b?2 charm most tracks from D decay.
• Combine S of tracks in jet into single joint
  probability variable PJ

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Charm counting in b decaysProbability Density
Functions and Fits
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Charm Counting in b decays Results

• measured for each year
  separately.
• Results for each year combined ? consistent.
• Two dominant systematics from physics modelling
• charged particle multiplicity in fragmentation
  (6.2)
• neutral K and ? multiplicities in D decays (
  )
• combined with
  and
• to yield nc.

7.2 - 4.6
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Conclusion

• Results of these recent OPAL charm counting and
  analyses consistent
  with previous measurements and theoretical
  predictions.

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Key variables
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Cross check of results

• angle between ?- and ?slow
• in rest frame of D.

sidebands
peak
Signal peaks at higher cos(?) while background
is flat.
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Extra slide charm counting