Sinad Farrington

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B Lifetimes and Flavour Tagging at CDF Run II

• Sinéad Farrington
• University of Glasgow
• for the CDF Collaboration
• European Physical Society
• Aachen, 17th-23rd July 2003

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Outline

• Overview of B Physics at CDF
• B lifetimes
• Exclusively reconstructed Bs decaying via J/?
• Semileptonically decaying Bs
• Flavour Tagging

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B Physics at CDF Run II
-
pp collisions produce a wide spectrum of B
hadrons in a challenging environment Tevatron
upgrade to 1.96 TeV CoM energy ? larger b
production cross section
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B Triggers at CDF Run II
-
-
?(bb) ltlt ?(pp) ? B events are selected with
specialised triggers
Di-Muon (J/?) pT(?)gt1.5 GeV/c
J/? modes at low (conventional)
pT( J/?) ? 0 GeV/c Measure
x-section (See talk by Tara Shears)
J/? Yield2x Run I
l displaced track pT(e/?)gt4 GeV/c
Semileptonic modes pT(trk)gt2 GeV/c
Lifetimes,flavour tagging 120
?mltd0(trk)lt1mm B Yields 3x Run I
NEW!
Two displaced tracks pT(trk)gt2 GeV/c
Hadronic modes 120 ?mltd0(trk)lt1mm Charm
Physics, B0s mixing
Indivdual data samples of about 140pb-1
accumulated
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B Hadron Lifetimes
According to the spectator model all B mesons
would have the same lifetime but that is not
the whole story! The HQE predicts by how much
the lifetimes differ. Objective 1 Measure
lifetimes accurately to form input to
theories Objective 2 Prove the detector and
triggers are working Objective 3 Measure
??s/?s B0s?l?Ds is an admixture of CP even and
CP odd states Pair it with fully CP even or
CP odd state (or use polarisation analysis) and
measure ??s/?s
PDG Values
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B Hadron Lifetimes

• SEMILEPTONIC
• leptondisplaced track trigger
• clean
• partially reconstructed
• - need MC to unfold ct
• lifetime biased
• good statistics

• EXCLUSIVE
• J/? trigger
• clean
• fully reconstructed
• lifetime unbiased
• low statistics

B0 ? l?D()- ?b ? l??c B0s? l? D?s
B0 ? J/? K0 B ?J/? K ?b? J/? ? B0s ? J/? ?

• Reconstruct decay length by vertexing
• Measure pT of decay products

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Exclusive B?J/?X Lifetimes
Fit Methodology Simultaneous fit of M(B) ?
signal fraction, define sidebands c?(B) ?
lifetime
Signal Contribution
Background Parameterisation
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?b?J/? ? Lifetime and Crosscheck
CONTROL SAMPLE
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Exclusive B?J/?X Lifetimes B0s Meson
Worlds largest sample of fully reconstructed Bs
mesons
B0s ? J/? ? is mostly CP even ?measures mostly ?L
component Access ??s/?s via angular analysis
coming soon
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Extraction of Semileptonic Lifetimes

• Lepton displaced track trigger implemented
  successfully for the first time!
• ? samples rich in B hadron semileptonic decays
• Follow the standard methodology
• reconstruct the D decay near to lepton
• B decay not fully reconstructed
• ?extract the ?? factor from Monte Carlo
• extract lifetime from decay length
• but with one crucial complication
• lifetime bias from the displaced vertex trigger
• 4 GeV lepton 2 GeV track with 120 ?mltd0 lt1mm
• Emulate trigger with Monte Carlo and model the
  lifetime bias
• which is factored into the fit function.

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K Factor and Bias from MC
K Factor Distribution P(K) Reconstruction
efficiency including trigger bias, as a
function of proper lifetime
Normalised to unit area
Arbitrary vertical scale
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B Semileptonic Channels
CDF Run II Preliminary 70pb-1
?b ? l??c
l
D?s
D?
M(pK?) (GeV/c2)
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Semileptonic Decay Fit Model

• Unbinned maximum likelihood fit to c?(B)
• Background is parameterised by delta function and
  positive exp convoluted with Gaussian resolution
• Free parameters ?D ?E ? f ?G
• Signal exp convoluted with Gaussian resolution,
  K factor distribution, P(K), and bias function, ?
• Maximum likelihood function

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Semileptonic Lifetime Fits
Highest statistical accuracy lifetime fits in B0s
and Lb
?b ? ???c
Control Samples

• Fit results show discrepancy with world average
• Many crosschecks
• Currently working to understand all effects of
  trigger bias etc.

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Flavour Tagging Development
SAME
OPPOSITE

• Determine B flavour at production
• and decay to measure
• B0 mixing, B0s mixing, CP violation
• Figure of merit ?D2
• ? tag efficiency
• D Right-Wrong/RightWrong
• CDF has a battery of tags which are
• being developed further

OPPOSITE SIDE Soft Lepton Tag
Opposite side K Tag Jet charge tag

SAME SIDE Same side K/? Tag
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Same Side Tag Asymmetry

• Identify fragmentation pion
• Measure raw asymmetry
• Test tagger on B ? should see NO oscillations!

B ? l?D0
B ? J/?K
For B0s mixing apply same side K tag very
powerful
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Tagger Studies in Semileptonic Sample

• lepton displaced track trigger provides high
• statistics sample of 150000 B (and D)
• semileptonic decays
• Strategy
• trigger lepton ? estimate of B flavour at
  production
• count numbers of opposite side tags
• can subdivide sample by muon system and pTrel
• parameterise relative dilution for use in
  likelihood fit
• cross check consistency with partially
  reconstructed leptonD,0
• consistent results ? believe dilution in
  leptonDs
• This number is UNBIASED since were using an
  independent (and high statistics) control sample

• Detailed sample composition studies
• Mass cut removes D decays 2ltM(ltrack)lt4GeV/c2
• Background subtraction variable separates Bs
  from
• background signed IP of displaced track

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Soft Muon Tag ?D2
Identify ? charge on opposite side Sufficient
statistics to examine parameterisation of
dilution as function of pTrel
Background subtraction has been used to obtain
measurement of ?D2
Soft Muon Tagger ?D20.660?0.093 CDF
Run I ?D20.584 ? 0.082

• Method will be used to evaluate, optimise and
  compare all taggers
• Unbiased way of optimising taggers
• Next step measure ?D2 for a reconstructed channel

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Summary

• Lifetime measurements made in clean B?J/?
  channels
• Lepton displaced vertex trigger has been
  implemented at CDF for the first time
• lifetime measurements ongoing will give best
  statistical accuracy in B0s and Lb
• Flavour Tagging procedure has been established
  and two taggers have been optimised and evaluated
  in a non-biased way
• Measurements of ??s/?s coming soon and first
  steps towards B0s mixing are happening!

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K Factor and Bias from MC
ELECTRONS
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• Major upgrades at CDF provide
• Increased geometric coverage
• Extended muon system
• new 3D silicon tracker
• faster response drift chamber
• Triggers large bandwidth, background
• reduction, displaced vertex triggering

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• Determine B flavour at production
• and decay to measure
• B0 mixing, B0s mixing, CP violation
• Figure of merit ?D2
• ? tag efficiency
• D Right-Wrong/RightWrong
• CDF has a battery of tags which are
• being developed further
• Run IIs leptondisplaced vertex trigger ? large
  sample of semileptonic decays
• allows us to measure ?, D and ?D2 in data and
  optimise the taggers
• can then apply them in any sample without bias

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