Measurement of bBaryons with the CDF II Detector

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Measurement of b-Baryons with the CDF II Detector
Joachim Heuser (University of Karlsruhe) for the
CDF Collaboration

• HEP 2007, Manchester

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Short Reminder b-Baryons

• b-baryon is system of one heavy b-quark and two
  light quarks
• Naming scheme as for light baryons, b replaces
  s-quark
• Status as of 2006 only ?b0 directly observed
• This talk ?b, ?b

?b lifetime result from CDF covered by M.Milnik
on Friday B meson results from CDF covered by
A.Gessler on Thursday
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Why Look for b-Baryons ?

• b-baryon interesting laboratory for understanding
  non-perturbative QCD and potential models
• heavy b-quark ? sizeable simplification in
  theoretical description
• basic model light diquark system qq surrounding
  the heavy b-quark nucleus Q
• coupling similar as in hydrogen/helium atom
• never bad to observe new states ?

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Expectations on ?b()

• light diquark system has isospin I1, spin j1
• isospin-triplet ?b , ?0b , ?-b (?0b singlet)
• diquark spin j1 can couple with b spin to J1/2
  (?b) or J3/2 (?b)
• Theory Predictions

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?b Search
Channel ?/-b ? ?b ?/- with ?b ? ?c ?-
and ?c ? p K- ? Search for resonances in
Qm(?b ?) m(?b) m(?)
?0b2800
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?b Event Selection

• exclude 0.03 lt Q lt 0.10 GeV region from signal
  selection procedure (blinding)
• optimize selection based on
• MC simulation for ? signal sample
• sidebands from data, containing only background
  events
• fix background contributions

• unblind

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?b Results
Observation of four signal peaks, associated with
?/-b() Significance of the signals gt5.2? (4
peaks vs. only BG) each peak gt3? (except
?b) Submitted to PRL arXiv0706.3868
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?b Masses
Good agreement with predictions !
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What Do We Know About the ?b ?

• quark content (usb / dsb)
• mass from extrapolation of charm baryons
• m(?b) - m(?b) m(?c) - m(?c)
• ? m(?b) m(?b) 180 MeV 5.8 GeV
• decay properties dominated by b-quark (with
  light quarks as spectators)
• ? expect similarities to other weakly decaying
  b-hadrons

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Decay of the ?-b

• Search in channel
• ?-b ? J/? ?-,
• with ?- ??0 ?-, ?0 ? p ?-

?- is charged, long-lived, particle ? can be
measured in silicon detector ? significantly
improves resolution ? improves background
suppression
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Selection Strategy

• Lifetime and energy released in decay similar
  between
• ?-b ? J/? ?- and B ? J/? K
• unbiased selection optimization on B ? J/? K
  sample

Keep 50 signal, reject factor 500 of background
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Observation of the ?-b

• Apply obtained selection on sample .

m 5792.9 2.5 1.7 MeV 7.7 ? significance
Submitted to PRL arXiv0707.0589
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Comparison

• In agreement with simultaneous observation by D0
  and theory predictions

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Summary Outlook

• CDF observed the ?-b baryon
• m(?-b) 5792.9 2.5 1.7 MeV
• arXiv0707.0589
• CDF observed the charged ?b() baryons
• arXiv0706.3868
• results in good agreement with theory
  predictions
• CDF working great, lets see what we can still
  do in the future (e.g. ?b lifetime) !

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Backup
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CDF II Detector

• Excellent tracking due to silicon layers near
  interaction point and large tracking volume
• Very important dedicated triggers for data
  selection

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?b Significance Determination

• Form likelihood ratios between different
  hypotheses (e.g. compare see 4 peaks to see
  only two)
• Ratios relative to 4-peak-hypothesis

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?b Cuts
Selection cuts for ?b
Selection cuts for ?b
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?b Backgrounds

• 3 main sources of background
• Hadronization and underlying events
• Tracks from hadronization of the b-quark,
  modelled by ?b PYTHIA MC
• Physics background
• Misidentified B, studied by B PYTHIA MC sample
• Combinatorial background
• Studied from upper data sideband

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?b Significance Determination

• Assume uniform distribution of background in mass
• Search window of 800 MeV
• Width of observed signal 75 MeV
• Binomial Probability of
• observing gt 18 events within 75 MeV bin
• from total of 23 events within 800 MeV