Limits on the Lifetime Difference DG of Neutral B Mesons and CP, T, and CPT Violation in B0B0 mixing

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Limits on the Lifetime Difference DG of Neutral
B Mesons andCP, T, and CPT Violation in B0B0
mixing

• Wouter Verkerke (UC Santa Barbara) for the BaBar
  collaboration

EPS2003 July 17-23 Aachen, Germany
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Introduction Flavor mixing in the Bd system

• Mass states BL, BH superposition of B0 and B0
  flavor states
• Properties of the system

IfCPT holds
Oscillation frequency
Well measured
Average life time
Well measured
NOT well measured
Life time difference
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Introduction CP,T,CPT violation in B0B0 mixing

• Increasing statistics of B factories ? precision
  measurements look at correction to naïve
  mixing picture CP/T/CPT violation in B0B0 mixing

1)
CPT violation
CP and CPT violation
? 0
Violated in mixing if
Locality ? CPT invariance (e.g SM 0)
2)
CP/T violation
CP and T violation
SMsmall
Violated in mixing if
3)
SM small ?
Life time difference DG
Usually assumed to be 0..
Best limit sofar DG/G lt 18 (90 CL)
Eur. Phys. J. C 28 (2003) 155-173

• Effect and magnitude on B decay rate measurement
  similar
• Need combined analysis to disentangle effects

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Coherent Time Evolution at the Y(4S)
PEP-II (SLAC)
B-Flavor Tagging
Exclusive B Meson Reconstruction
Vertexing Time DifferenceDetermination
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Time dependent B decay rates naïve mixing picture
Differential event rate, as a function of the
difference between the proper decay times of
the two B mesons in the final state
Assume DG 0, no CP/T/CPT violation
Oscillations with frequency Dm
Exp. Decay
Decay time distributions
Mixed Unmixed Mixed Unmixed
ftag ? frec (unmixed)
ftag frec (mixed)
Asymmetry
Decay rate
Decay rate
-15 0 15
Dt (ps)
-15 0 15
Dt (ps)
-15 0 15
Dt (ps)
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Time dependent B decay rates allowing DG?0,
CP/T/CPT violation
Full expression much more complicated
Allow DG ? 0
?
1 if DG0
Allow CP/CPTviolation
1 w/o CP/CPT violation
Absent w/o CP/CPT violation
If z ? 0 Prob(B0 ? B0,t) ? Prob(B0 ? B0,t)
New parameterization allows to test conventional
assumptions on CP/T/CPT violation in mixing
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Variation B decay into CP eigenstates
Allow DG ? 0
?
Different expression for coefficients C and S
complex CP-parameter characterizes
interferencebetween mixing decay
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Effect of DG?0, CP/T/CPT violation on B decay rate
Flavor eigenstate sample
Sensitive top/q Im(z)Dm DG (2nd order)
t-parityevenoddeven
unmixed
mixed
Effect of q/p opposite for B0/B0
Naïve model DG/G 20 q/p 0.9 Im(z)
0.1
CP eigenstate sample
t-parityevenoddodd
Sensitive toRe(z)lCP DG (1st order)
Naïve model Re(z) 0.2 DG/G 20 q/p
0.9
(Untagged eventsalso sensitive to DG/G)
Clearly a precision measurement, effects of
detector performance not even yet included
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The measurement Data Samples
Nov 1999- June 2002 data ? 82 fb-1 on-peak 88
million BB pairs
Samples of B decays to flavor-specific final
states
(31000 events)
charge conjugate decays are implied, unless
specified
Samples of B decays to CP-eigenstates with
charmonium .
(2600 events)
CP -1
CP 1
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The measurement Fit Procedure

• Effects of (DG?0, CPT violation) small ? be
  precise
• Take -level physics effects that can fake
  CP/CPT/DG into account
• Accurate detector response modelling
• Simultaneous fit for q/p, DG/G, Dm, Im(z),
  Re(z) and lCP to time-dependence of CP and
  flavor eigenstates, including tagged and untagged
  events

FitModel
? Detector response(Dt, ftag, frec)

• Account for
• Possible direct CP violation in the CP
  eigenstate sample (lCP)
• Correlation between reco B and tag B via
  interference between CKM-allowed and
  doubly-CKM suppressed decays

• Account for
• Incorrect assignments of the flavour tagging
  algorithm (separate mistag fractions for B0
  and B0bar)
• Dt resolution that is comparable to the B
  life time and asymmetric for positive and
  negative dt (triple Gaussian Dt resolution
  model)
• Account for possible asymmetries in detector
  response for positive and negative particles

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Results Limits on DG, search for CP,T,CPT
violation in mixing
Preliminary result
SM ?-0.003
Mixing
Best limit so far DG/Glt20, big improvement
Eur. Phys. J. C 28 (2003) 155-173
SM q/p-1 ? 5?10-4
CP T violation
S i m u l t a n e o u s f i t
SM 0
CPT CP violation
SM 0
90 CL intervals
Physics parameter correlations O(5), largest
correlation 17
(Assuming CPT invariance Consistent with above
results)
Mixing
CP T violation
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Results Limits on DG, search for CP,T,CPT
violation in mixing
(CP/CPT violation)
(CP/T violation)
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Summary

• First simultaneous measurement of DG/G, CP, T
  and CPT violation in the B0 system
• Hadronic data sample Nov 1999 June 2002 (82
  fb-1)
• Much improved limit on DG/G
• DG/G lt 20 (90 C.L., PDG 2003 (DELPHI)) ?
  DG/G lt 8 (90 C.L. this analysis)
• Measurement of CP and T violation (q/p)
  consistent with Standard Model expectation
• Also consistent with previous BaBar measurement
  using di-lepton events
• Strongest test of CPT invariance outside K0
  system to date
• BaBar (2003) Im(z) 0.038 ? 0.029 ? 0.025
  Re(z) 0.014 ? 0.035 ? 0.034
• Belle di-Lepton (2002) Im(z) -0.03 ? 0.01 ?
  0.03 Re(z) 0.00 ? 0.12 ? 0.02
• OPAL Z ? bb (1997) Im(z) 0.040 ? 0.032 ?
  0.012

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(Backup slides)
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Correlations between physics parameters
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Summary of systematic uncertainties