Lake Louis Winter Institute

1
Recent b-physics Results from CDF

• Giorgio Apollinari
• Fermilab
• for the CDF Collaboration
• Introduction
• CP Violation and b Mixing
• Rare B Decays
• Polarization in B V V
• Future Prospects

Lake Louis Winter Institute 20-26 February 2000
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Introduction

• B-physics is
• Study of the Weak Decays
• Test the CKM Mechanism
• Study b-mesons and b-barions spectroscopy Bs,
  Lb, Bc
• Look for New Physics in Rare Decays
• e.g. B0, Bs mm or em
• Quantitative study of QCD
• mb gtgt LQCD implies that inclusive production can
  be computed through Perturbation Theory
• Probe gluon structure function
• Also perform non-perturbative measurements like
  lifetimes, BF and production fractions.

3
Introduction

• Tevatron Advantage
• Large production
• All b-hadron states produced
• Bu,Bd,Bs,Bc,Lb
• Tevatron disadvantage
• Large Background (sin 1000 x sbb)
• b-production peaked at low pt
• Unknown initial state
• Experimental Strategies
• Specialized triggers
• dilepton single lepton
• J/y, y from (ee,mm) B mixing from (em, ee,
  mm),
• b-hadron semileptonic decays
• Precise Secondary Vertex reconstruction

4
b-physics at the Tevatron

• Examples of Run I b-physics results from CDF

5
b-Mixing and CP Violation

• SM with 3 generations and mixing among the quark
  families (mass eigenstates ? weak eigenstates)
  can accomodate CP violation if the complex phase
  in the unitary mixing matrix ? is ? 0?CP.
• In the B0d,s case, like in the Ks system,higher
  order weak interactions mix meson and anti-mesons
  states.

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b-Mixing and CP Violation

• Unitary Triangle representation
• from unitarity of CKM
• S. Mele CERN-EP-98-133, 1998 sin2?0.75? 0.09
• Parodi et al. hep-ph/9802289 sin2?0.725? 0.06
• Ali et al. 0.52ltsin2?lt0.94

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b-Mixing and CP Violation

• CP violation can be manifested as
• CP violation in the decay if A(f)/A(f) 1
• CP violation in the mixing if the neutral mass
  eigenstates are not CP eigenstates (q/p 1)
• CP violation in the interference between decays
  with and without mixing
• Vtd introduces a complex phase in the box diagram
  and the interference between the two terms leads
  to a time dependent asymmetry
• Golden mode

B0
J/y K0s
B0
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b-Mixing and CP Violation

• Time integrated ACP does not vanish at hadron
  colliders (since the B0B0 system is not produced
  in a coherent state)
• PDG 98
• A measurement of the proper time dependence of
  ACP(t) is preferable
• more statistical power
• reduces effect of combinatorial background at
  small t

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b-Mixing and CP Violation

• Measurement of ACP(t) requires 3 pieces of
  information for each decaying meson
• Signal Reconstruction
• Flavor of original meson
• Use flavor tagging
• Proper time of decay
• Reconstruct the B vertex
• Tagging algorithms characterized by efficiency e
  and dilution D
• AobsCP D ACP
• D dilution
• NtotTotal number of events
• NWNumber of wrong tags
• NRnumber of right tags
• D2P-1 (Pprob. of a ccorrect tag)
• Best tagging has highest e D2

• Opposite Side Lepton and/or Kaon tagging (OST)
• Use decay of the away side B-hadron
• Opposite Side Jet-Charge tagging
• Reconstruct the away-side B-hadron and use
  statistical methods to determine the flavor
• Same Side tagging (SST)
• Uses correlation with p produced along with the
  B-hadron being tagged
• Correlation from the B and fragmentation

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b-Mixing and CP Violation

• Same Side Tagging
• uses correlation between the charge of the nearby
  p and the b quark charge due to fragmentation or
  B production
• Gronau, Nippe, Rosner
• p (K) tags a B0 and a p- (K-) tags a B0
• better acceptance (efficiency) than OST

• Track Selection
• DRlt0.7 from B meson
• pT gt 400 MeV
• gt2 SVX hits
• consistent with primary vtx in r-f and z
• minimum prelT

B direction
PB Ptr
PB
Ptrrel
Cone ?R0.7
Ptr
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b-Mixing and CP Violation

• SST and mixing measurement

Mostly Charge Bs
Amplitude gives D
Mostly Neutral Bs

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b-Mixing and CP Violation

• First measurement of sin2b
• F.Abe et al., Phys. Rev. Lett. 81, 5513
• 198/- 17 B0,B0bar events
• Asymmetry measured with SST
• D sin2b0.31 ? 0.18 ? 0.03 (syst.)
• D0.166 ? 0.018 ? 0.013
• sin2b1.8 ? 1.1 ? 0.3
• Improvements
• candidates not fully reconstructed in SVX
• 400 events, larger s(t)
• Add OST
• calibrate using B- J/y K-
• Multiple taggers
• use maximum L to include terms for possible
  detector biases, prompt bkg. And long-lived
  bkg.

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b-Mixing and CP Violation

• Signal sample in Run I

Both ? in SVX
202 ? 18 events
395 ? 31 events
S/B0.9
One or Both? not in SVX
193? 26
S/B0.7
S/B0.5
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b-Mixing and CP Violation

• Taggers Calibration on un-mixing B/B- samples

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b-Mixing and CP Violation

• Combination of flavor taggers
• Correlations
• Multiple tags
• Fixing Dmd0.464?0.018 ps-1
• Dmd floating

• Time integrated

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b-Mixing and CP Violation

• Systematics
• Dilution 0.16
• dominated by statistic in the calibration samples
  
• Others 0.02

• Confidence Limit
• 0ltsin 2b lt1 at 93 CL
• if sin2b 0, the probability of observing
  sin2bgt0.79 is 3.6

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b-Mixing and CP Violation

• Conclusive Evidence for CP violation in B sector
• Summary of sin 2b determinations
• OPAL Euro. Phys. C5, 379 (98)
• CDF(Partial) PRL 81, 5513 (98)
• CDF(Final) hep-ex/9909003
• ALEPH (Prelim.) BCP3 Taipei, Dec. 99
• AVERAGE

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Rare b Decays

• Flavor Changing Neutral Current
• Limits on Bo/Bs mm-
• F.Abe et al, PRD 57, R3811 (1998)
• Allowed by SM, 3 orders of magnitude below
  current sensistivity
• Some SUSY models predict substantial enhancement

• Lepton Number Conservation
• Limits on Bo/Bs mm-
• F.Abe et al, PRL 81, 5742 (1998)
• Forbidden in SM
• Sensitive to new particles (e.g. Pati-Salam
  Leptoquarks)

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Rare b Decays

• Non Resonant B mm K and charmless decays
• Allowed by SM, sensitive to presence of new
  particles

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B VV Polarization

• Decay distributions in
• described by 3 complex amplitudes

• Yields CP Composition
• - is parity-odd (L1)
• Is a pure CP state?

21
B VV Polarization
22
Tevatron Run II B-Physics

• CDF Upgrades
• New Silicon Tracker, 96 cm long, r-z and r-f
  measurements
• 2 times more acceptance
• New dead-time-less trigger
• Tracking information used at L1
• Use Silicon information at L2
• Purely hadronic B trigger possible
• Time-of-flight
• 2s K/p separation at plt1.6 GeV/c
• D0 Upgrades
• Superconducting Solenoid
• Central Fiber Tracker
• Silicon Microstrip Tracker

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Tevatron Run II B-Physics

• Precise Measurement of Vtd/Vts
• flavor oscillation and
  , sensitive to xslt63
• Radiative Decays
• Precise Measurement of CP violation and sin 2b
  in
• Observe CP violation and measure asymmetry in
• Measure CP asymmetry in
• Observe decay modes related to the angle g
• Rare Decays
• Study Bc meson and b-barions
• Unique to Hadron Machines

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Tevatron Run II B-Physics

• Expectations for CP modes
• sin 2b from B0 J/y Ks0
• 10K reconstructed J/y Ks0
• Taggers calibrated on
• 40K B J/y K
• 20K B0 J/y K0
• eD26.7 (add 2.4 with TOF)
• d(sin2b)0.084
• Asymmetry in B0/B0 pp- (sin2a)
• 8K-15K signals (if BR 10-5)
• If signal 10K and eD2 9.1
• dA(pp- ) 0.09
• sin(g) modes
• 700 events of Bs0/ Bs0 DsK

Next phase in b-physics investigation is around
the corner