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Search for CP Violation in B0??h decays and
B0??h decays with BABAR
Christophe Yèche (CEA-Saclay, DAPNIA/SPP)

• Outline
• CP asymmetries in ??- and ?K- (PRL, 89, 281802
  (2002))
• Decay rates for ??0 and ?0?0 (submitted to
  PRL, hep-ex/0303028)
• CP asymmetries in ??- and ?K- (submitted to
  PRL, hep-ex/0306030)
• Decay rates for ??0, ?0? and
  ?0?0(BABAR-CONF-03/014)

International Europhysics Conference on High
Energy Physics , July 17th-23rd, 2003, Aachen,
Germany
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CP Violation in Standard Model

• CP symmetry can be violated in any field theory
  with at least one non-trivial phase in the
  Lagrangian
• This condition is satisfied in the SM through
  the three-generation CKM quark-mixing matrix
• Unitary constraint

• Representation with Unitary Triangle
• The angles (?,?,?) are related to CP
• violating asymmetries in specific B decays
• ? is already measured with good
• precision Sin2? 0.734 0.055
• Next step measurement of sin2?

a
B0?pp, rp
?
b
g
?
B0?J/yKS
B0?DK
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CP Violation in B0??? -
Penguin diagram
Tree diagram
Vtd

Vub
A(penguin)/A(tree) 30
For single weak phase
With an additional weak phase
? ? 1 ? must fit for direct CP Im (?) ? sin2?
? need to relate asymmetry to ?
Cpp 0, Spp Im (?) sin2a
Cpp ? 0, Spp sin2aeff
Cpp ? 0, Spp sin2aeff
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Experimental technique
Exclusive B Meson Reconstruction CP
eigenstates Flavor eigenstates
Inclusive Reconstruction B-Flavor Tagging
(flavor eigenstates) Resolution
function and mistags
(CP eigenstates) CP analysis
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Background suppression- Discriminating variables
?E some separation power for final states with
different K/? composition
mES powerful variable to separate signal from
light-quark continuum
mES and ?E are used in the likelihood
?(DE) ? 26 MeV
s(mES) ? 2.6 MeV/c2
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Continuum suppression- Discriminating variables
? candidate
? candidate
Jets
Rest-Of -Event
? candidate
? candidate

• Spherical B events vs jet-like continuum
• Techniques exploiting event topology and angular
  distributions
• Fisher variable
• Combine two monomials,
• where the sum is over the tracks i of the
  Rest-Of-Event
• Use as a discriminating variable in the
  Likelihood

and
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PID K/? Separation

• DIRC
• Cherenkov light emitted by the track around a
  cone with
• Photons are captured by internal reflection in
  the bar and transmitted to a PMT matrix.
• Resolution ?(?c) 2.5 mrad (ee-???-)

Cherenkov angle ?c is used in the likelihood to
separate ??, ?K, KK
8 ? at 2GeV/c 2.5 ? at 4GeV/c
K hypothesis
p hypothesis
K/? momentum 2 ?4 GeV/c
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B0??? -/ K? - / KK- Branching Fractions
Projection plots
B0???-
B0???-
The yields are extracted from a maximum
likelihood fit based on the variables mES, ?E, F
and ?c
Continuum ee- ? q q
Kp
N(B0? ??-) 157 19 7
B0?K?-
B0?K?-
Continuum
pp
N(B0? K?-) 589 30 17
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CP Asymmetry Results for ?-? /? -K
No Observation of CP Violation
The CP parameters are extracted from a maximum
likelihood fit based on the variables mES, ?E, F
, ?c and ?t (for C and S)
ACP (?K) -0.102 ? 0.050 ? 0.016 C?? -0.30 ?
0.25 ? 0.04 S?? 0.02 ? 0.34 ? 0.05
A(B0/B0)
Cross-checks Float t and Dmd
B0?K?-
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Constraint on ? Isospin Analysis

• The decays B ? pp-, pp0, p0p0 are related by
  isospin
• Two relations (one for B0, one for B0)
• Neglecting EW penguins, B ? pp0 is pure
• tree diagram
• Representation with a triangle with a common
  side.
• Need to measure separate BF for B0/B0 and B/B-
• Triangle relations allow determination of
  penguin-induced
• shift in ?
• Bound on penguin pollution
• Back up solution if the BF(p0p0)
• is too small for isospin analysis!!!

M. Gronau and D. London, Phys. Rev. Lett., 65,
3381 (1990)
Y. Grossman and H.R. Quinn, Phys. Rev., D58,
017504 (1998)
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B? ?0?0 /??0 BF
Fit region
rp-

• B???0 decays
• Likelihood fit with mES, ?E, F and ?c
• Potential ??- background suppressed
• with a tight cut on ?E
• B0??0?0 decays
• Likelihood fit with mES, ?E, F T
• Potential ??0 background suppressed
• with a cut on M(??0) and on ?E(??0 ?0)
• Bound on penguin pollution

Continuum
p0p0
?p0
Continuum ee- ? q q
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Interpretation

• Isospin Analysis
• Large upper limit for BF(B0??0?0)
• Confidence levels obtained with the
• BABAR measurements of C??, S??,,
• BF(B0??0?0) and BF(B???0)
• Independent of models but no constraint
• in (?,?) plane
• QCD factorization
• The phase and the magnitude of the tree
• and penguin amplitudes are predicted by
• the QCD factorization.
• Confidence levels obtained with the
• BABAR measurements of C?? and S??.
• Very strong constraint in (?,?) plane.

BBNS, Nucl. Phys., B606, 245 (2001)
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How to measure ? with B0??? ?

• Two final states
• Same diagrams as B0??- ?, related to ? angle
• Final states are not CP eigenstates
• Two parameters (C??, S??)
• ? Four parameters (C??, S??, ?C??, ?S??) charge
  asymmetry ?-/?
• Comparison with B0??- ?
• Larger Branching Fractions (?4)
• Smaller ratio A(penguin)/ A(tree)

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Parameters measured in the the ??/?K analysis

• Time probability of the B0? ??/?K

• 4 CP Violation Parameters
• Direct CP Violation with the charge asymmetries
  (?/?-) ACP?0 for K and ?.
• Summing over the ? charge, we have the usual
  (B0/B0) asymmetry
• Direct CP Violation C?? ? 0
• CP in interference between decay and mixing S??
  ? 0
• 2 Dilution Parameters
• ??C?? can be different from zero (naïve
  factorization??C0.3).
• ??S?? can be different from zero, no prediction
  for this term.
• if ??C??0 (P(B0/B0???-)P(B0 /B0??-?)) and
  ??S??0
• ? no dilution of sin(2?eff) when S?? is
  measured!

Parameterization similar to B0???-
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Overview of ??/?K analysis

• Analysis very similar to ??/?K analysis
• Same data set (1999?2002) 81 fb-1.
• Tagging and resolution function studied with
  fully reconstructed events.
• Simultaneous fit of ?? and ?K events.
• Extraction of a the CP parameters with a maximum
  Likelihood fit using the same kind of variables
  mES, ?E, F /NN, ?c and ?t.
• Features specific to ??/?K analysis
• Continuum Suppression NN with L0, L2 and two
  additional variables
• ? Mass (mass of the pair (??0)).
• ? Helicity (angle between ?0 and B in ? rest
  frame).
• Modeling of true-signal and misreconstructed-sign
  al.
• Modeling of charm and charmless B backgrounds.

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B0???/?K Branching Fractions
??
??
Continuum B background
Continuum
Continuum
Continuum B background
Projection plots
?K
?K
Continuum B background
Continuum
Continuum
Continuum B background
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CP AsymmetryResults for ??/?K
??
ACP (??) -0.18 ? 0.08 ? 0.03 ACP (?K) 0.28 ?
0.17 ? 0.08 C?? 0.36 ? 0.18 ? 0.04 ?C?? 0.28
? 0.18 ? 0.04 S?? 0.19 ? 0.24 ? 0.03 ?S??
0.15 ? 0.25 ? 0.03
?
Continuum B background
B background
?

• See P-F Girauds Talk, about direct CP
  Violation.
• By combining C??, ?C?? and ACP (??) ? a little
  more than a 2? effect for direct CP Violation.

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B? ?0?0 /??0/ ?0? BF

• Principle of the analyses
• Approach very similar to B0???-
• Likelihood fit with mES, ?E,
• NN and (?t)
• Next steps
• Isospin analysis (more complicated)
• Two triangles ? Two pentagons
• Interpretation with QCD factorization
• For a first attempt, see next slide.
• (?0?-?) Dalitz plot analysis.

B0? ?0?0
Continuum B background
Continuum
First observation !!!
B? ??0
Continuum
Continuum B background
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Interpretation with QCD factorization

• Direct CP with QCD factorization
• In recent papers, computation of QCD
• factorization for PV decays (??,)
• QCD Factorization predicts very
• small direct CP violation for ??-, better
  agreement with charming penguin.
• Mixing-induced CP Violation
• C.L. in (?,?) plane the BaBar
• results for the S?? and ?S?? with
• the computation of QCD
• factorization for PV decays

R. Aleksan et al., Phys. Rev. D67, 094019
(2003) See S. Safir Talk
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Conclusions

• BABAR results
• No observation of CP Violation in B0???-.
• A hint of direct CP Violation in B0???-.
• No observation of B0??0?0 and B0??0?0 decays.
  
• First observation of B???0 decay.
• Prospects
• The isospin analysis does not constrain ? yet.
• QCD factorization may give very strong
  constraint on ?
• but still needs to be validated.
• The redundancy in experimental measurements
  (B0???-, B0???-,
• and B0???-) may provide a solid framework to
  test theoretical models and to extract ?.

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