First Observation of the Baryon Properties of , , , and Baryons

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First Observation of the BaryonProperties
of , , , and Baryons

• Andreas Warburton
• Cornell University
• CLEO Collaboration
• XXXth International Conference on High Energy
  Physics
• ICHEP 2000, Osaka, Japan
• July 27 ? August 2, 2000
• PA01c50

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Talk Overview
All new results are preliminary!

• Charmed-Baryon Spectroscopy
• CLEO Charmed-Baryon Reconstruction Techniques
• Mass and Width Measurements of the and
  Baryons
• Discovery of and Mass Measurement of the
  Baryon
• First CLEO Observation of the Baryon

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The Charmed Baryons
Charmed baryons consist of a heavy c
quark and a light diquark ? Many JP states To
date, all L0 states seen except
and None of the JP quantum numbers has
been measured!
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and Spectroscopy
Not yet observed
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Data Set and CLEO II/II.V Detector
ee? Collisions near Resonance (10.5 GeV)
Charm-quark Production B-meson decays
ee? ? cc jets
Two Configurations CLEO II (1989 ?
1995) CLEO II.V (1996 ? 1999)
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Reconstructed Candidate Modes
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Event Selection and Background Suppression
Principles

• candidates are reconstructed in the CsI
  calorimeter barrel region
• candidates are identified using
  time-of-flight and dE/dx info
• Displaced vertices are used to identify
  candidates
• Scaled Momentum criterion xp 0.5 or 0.6,
  where xp ? p/pmax
  and
• reduces combinatorial background
• Note charmed baryons with B-meson parents have
  xp

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15 Modes

• xp 0.5
• Signal region ?1.6?
• Yield 58 000 candidates
• SN 1 1.2

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Inclusive Hyperon Samples
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and Massand Width Fits
Resolution Function

• Double-Gaussian resolution function (? 0.6
  MeV/c2)
• Yields 2000 events
• Fit to p-wave Breit-Wigner convolved with
  resolution function
• xp 0.5

Resolution Function
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and Yields

• Mass Fits to p-wave Breit-Wigner convolved
  with resolution function
• xp 0.6
• First observation of resonance

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CLEO Mass and Width Measurements

• PRELIMINARY CLEO results
• G. Brandenburg et al. (CLEO), Phys. Rev. Lett.
  78, 2304 (1997)

All quantities are in . First
uncertainties are statistical second are
systematic.
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Search Modes
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Sum of 5 Search Modes
Wrong-Sign Daughter Combinations Hyperon-Sideband
Distributions
Total Fitted Yield 40.4 ? 9.0 (stat.)
candidates
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Summary of Preliminary Results
Unbinned maximum likelihood fit mass
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Conclusions

• We present the most statistically accurate
  measurements of the , , and
  masses.
• We have made preliminary measurements of the
  and widths.
• We report the first observation of the
  baryon and measure its mass to be

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Conclusions, contd

• CLEO has now, for the first time, observed a
  significant number of candidates. We
  present a preliminary mass measurement of
• Supporting documentation can be found in
• hep-ex/0007041
• hep-ex/00070
• CLEO continues to contribute to knowledge of the
  charmed baryon sector.