Wouter Verkerke, UCSB

Limits on the Lifetime Difference 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

Wouter Verkerke, UCSB

-1 0 1 E (ps-1)

Introduction: Flavor mixing in the Bd system

• Mass states BL, BH superposition of B0 and B0 flavor states

• Properties of the system:

Oscillation frequency Well measured

Average life time Well measured

Life time difference NOT well measured

IfCPTholds

Wouter Verkerke, UCSB

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

SM:small1p

q 41051 p

q

CPT violation

CP/T violation

Life time difference SM: small

Usually assumed to be 0..

Locality CPT invariance (e.g SM: 0)

Violated in mixing if

Effect and magnitude on B decay rate measurement similarNeed combined analysis to disentangle effects

Best limit sofar: / < 18% (90% CL)

CP and T violation

CP and CPT violation

Violated in mixing if 0

1)

2)

3)

Eur. Phys. J. C 28 (2003) 155-173

Wouter Verkerke, UCSB

Coherent Time Evolution at the Y(4S)

B-Flavor Tagging

Exclusive B Meson

Reconstruction

Vertexing &Time DifferenceDetermination

PEP-II (SLAC)

Wouter Verkerke, UCSB

Time dependent B decay rates: naïve mixing picture

Exp. Decay Oscillations with frequency m

Differential event rate, as a function of the difference between the proper decay times of the two B mesons in the final state Assume = 0, no CP/T/CPT violation

)cos(11

))4(( || tmeffBBSYNtd

d trectag

ftag frec (unmixed) ftag = frec (mixed) Mixed – UnmixedMixed + Unmixed

Decay time distributions

Deca

y r

ate

Deca

y r

ate

Asy

mm

etr

y

-15 0 15 t (ps)

-15 0 15 t (ps)

-15 0 15 t (ps)

Wouter Verkerke, UCSB

Time dependent B decay rates allowing 0, CP/T/CPT violation

Full expression much more complicated…

New parameterization allows to test conventional assumptions on CP/T/CPT violation in mixing

=1 if =0

with

and

Allow 0

=1 w/o CP/CPT violation Absent w/o CP/CPT violation

Allow CP/CPT

violation

If z 0 Prob(B0 B0,t) Prob(B0 B0,t)

Wouter Verkerke, UCSB

Variation: B decay into CP eigenstates

Allow 0

complex CP-parameter characterizes interferencebetween mixing & decay

Different expression for coefficients C and S

Wouter Verkerke, UCSB

Effect of 0, CP/T/CPT violation on B decay rate

unmixed mixed

B0 B0

Flavor eigenstate sample

CP eigenstate sample

Sensitive to:|p/q|Im(z)m

(2nd order)

Sensitive to:Re(z)

CP

(1st order)

Naïve model& / = 20%& |q/p| = 0.9& Im(z) = 0.1

Naïve model& Re(z) = 0.2& / = 20%& |q/p| = 0.9

Effect of |q/p| opposite for B0/B0

Clearly a precision measurement, effects of detector performance not even yet included…

t-parityevenoddeven

t-parityevenoddodd

(Untagged eventsalso sensitive to /)

Wouter Verkerke, UCSB

The measurement – Data Samples

before tagging and vertexing cutsSamples of B decays to flavor-specific

final states

Samples of B decays to CP-eigenstates

with charmonium .

charge conjugate

decays are implied, unless specified

Nov 1999- June 2002 data 82 fb-1 on-peak – 88 million BB pairs

CP = +1

CP = -1

(31000 events)

(2600 events)

Wouter Verkerke, UCSB

The measurement – Fit Procedure

• Effects of (0, CPT violation) small be precise– Take %-level physics effects that can fake CP/CPT/ into account

– Accurate detector response modelling

– Simultaneous fit for |q/p|, /, m, Im(z), Re(z) and CP to time-dependence of CP and flavor eigenstates, including tagged and untagged events

Account for

– Possible direct CP violation in the CP eigenstate sample (CP)

– 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)

– t resolution that is comparable to the B life time and asymmetric for positive and negative dt (triple Gaussian t resolution model)

– Account for possible asymmetries in detector response for positive and negative particles

FitModel Detector response(t, ftag, frec)

Wouter Verkerke, UCSB

Results – Limits on , search for CP,T,CPT violation in mixing

90% CL intervals

Mixing

CP & T violation

CPT & CP violation

Mixing

CP & T violation

S i m

u l t

a n

e o

u s

f

i t

Preliminary result

SM: 0

SM: 0

SM: -0.003

SM: |q/p|-1 510-4

Best limit so far <20%, big improvementEur. Phys. J. C 28 (2003) 155-173

Physics parameter correlations O(5%), largest correlation 17%

(Assuming CPT invariance – Consistent with above results)

Wouter Verkerke, UCSB

Results – Limits on , search for CP,T,CPT violation in mixing

Preliminary result

Also represented: constraint on indirect CPV using dilepton sample

Phys. Rev. Lett. 89 (2002) 201802

(CP/T violation)

(CP/C

PT v

iola

tion)

Wouter Verkerke, UCSB

Summary

• First simultaneous measurement of /, CP, T and CPT violation in the B0 system

– Hadronic data sample Nov 1999 – June 2002 (82 fb-1)

• Much improved limit on /– / < 20 % (90% C.L., PDG 2003 (DELPHI))

/ < 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 0.03Re(z) = 0.00 0.12 0.02

– OPAL Z bb (1997) Im(z) = 0.040 0.032 0.012

Wouter Verkerke, UCSB

(Backup slides)

Wouter Verkerke, UCSB

Correlations between physics parameters

Wouter Verkerke, UCSB

Summary of systematic uncertainties