Measurement of LB Lifetime in the Decay Channel LBJY L

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Measurement of LB Lifetime in the Decay
ChannelLB-gtJ/Y L
Chunlei Liu University of Pittsburgh For the CDF
Collaboration APS Meeting April 22-25

• Theoretical expectations from HQET
• Current experimental situation.
• Analysis techniques and results.
• Systematic errors and reality checks
• Future prospects

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Exclusive B Hadron (B/B0/B0s/Lb) Decays
In the spectator model, b hadron lifetime is
attributed to the decay of the b quark in the b
quark in the hadron
d
In this model all b hadron lifetimes are
equal However this situation is modified by
nonspectator effects
W
u
b
c
d
d
Weak Scattering 7 t(Lb)
Pauli Interference 3 t(Lb)
c
b
b
c
d
d
W
W
u
d
d
d
d
u
Nonspectator effects have a large effect in the
charm sector, but are much smaller in the bottom
sector (corrections 1/mb2)
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HQET Predictions t(B)/t(B0) 1 -
1.1 t(Bs)/t(B0) 0.99 -
1.1 t(Lb)/t(B0) 0.9 -
1.0 Theoretically most likely value for
t(Lb)/t(B0) 0.94 (I. Bigi, N. Uraltsev, private
communication) Lb is not produced at the B
factories, but produced copiously at CDF where B
hadrons are produced democratically. It can be
observed in semileptonic decays, hadronic
decays, and the fully reconstructed
Lb?J/y L (this analysis)
Current knowledge of t(Lb) comes from the
Tevatron and the LEP experiments.
HFAG 2005 World Average t(Lb)/t(B0) 0.803
0.047 The theory is uncomfortable with this
experimental situation.
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CDF Has 1fb-1 of data and a large number of fully
reconstructed exclusive final states of B
hadrons similar trigger and analysis techniques
will allow Precision determination of lifetime
ratios.
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• All of these modes are fully reconstructed, very
  clean and largely
• free of physics background.
• This talk summarizes the measurement of the Lb
  Lifetime in Lb ? J/? Lb, based upon 370 pb-1 of
  data collected from Feb 2002 August 2004
  (subset of luminosity in above plot).
• We include results in our control sample B0? J/?
  K0s.

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Topologies
Use our control mode to validate the analysis
procedure, as well as to study any systematic
error resulting from the V0 topology of the
decay.
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CDF Detector Silicon system for impact
parameter Drift chamber for trigger, pT
Muon chambers for trigger, Muon ID.
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K0 or L0 opens in or after silicon detectors.
Neutral track has large transverse errors.
Anatomy of the Lb?J/y L decay mode.
Decay distance is the distance between the
primary interaction vertex and the B decay
vertex. B decay vertex is estimated using only
the muons from the J/y -can calibrate
resolution function -same systematics on all
B decays to J/y X
Two muons from J/y decay required at the trigger
level (no bias on decay length).
At least 3 silicon hits are required on
both muon for precision tracking information.
Beam spot
the L0 ( or Ks0) is required to point to the
J/y vertex.
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Propagation of tracking information from hits to
lifetime Hits ? Tracks Tracks? Beam spot
vertices Vertices? Transverse decay
length Transverse Decay Length-gt Proper Decay
Length
Proper decay time for full dataset? t (Lb)
using Unbinned Maximum Likelihood fit.
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Three variable fit 1. Proper decay length
(PDL), 2. Mass 3. PDL
Estimated Error
To a two component model 1. Signal. 2.
Background (prompt, longlived, negative tail)
Bkg (dE1E2E3) ? G
Signal E ? G
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Fit Result I Projection onto mass variable.
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Fit Result II Projection onto lifetime
variable.
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Fit Result III Projection onto proper decay
time error variable. (Note, this piece of the
likelihood function is required for an
unbiased fit since event-per-event errors are
used)
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Variations of the fit model in Mass Space, PDL
Space, PDL Error Space including possible
departures from the standard single Gaussian
resolution function, different background
models SVX Internal and SVX/COT
Alignment Special Systematic Errors arising
from the V0 through possible (though
undetected) selection bias
3.7 mm for B0 5.2 mm for Lb
3.0 mm for B0 3.8 mm for Lb
1.0 mm
Impact Parameter Distortions In COT??
4.9 mm for B0 6.6 mm for Lb
for a total systematic error of
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Sanity check lifetimes measured in many
different decay modes of B0 and B, all
consistent with each other and with world ave.
Statistical uncertainties only.
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Summary

• We measure the decay mode Lb-gtJ/Y L0
• We measure in our control decay mode B0-gtJ/y Ks
• Consistent with PDG 2004 value of 1.5360.014
  ps
• Using our t(Lb) measurement and PDG 2004 t(B0)
• Result 1.4 s larger than the world average and
  in good agreement with theoretical expectations.
• New results with the full data set and complete
  set of exclusive lifetimes will be

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Backup Slides
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Systematic Uncertainties

• Fitter bias
• toyMC studies
• Fit Model
• Variations in choice of resolution function,
  signal background models consistent with data
• Probe mass/PDL correlation
• PV determination
• Different beamline-z choice
• Alignment
• SVX internal
• SVX-COT global (tanslation,rotation)
• V0 Pointing
• PDL-dependent bias from V0 to J/y pointing
  constraint