Measurements of CP violation at Belle

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Measurements of CP violation at Belle

• Outline of Presentation.
• The Belle Experiment
• Generic Indirect CP violation measurements.
• Results for sin(2?1)
• Results for ?2
• Results for ?3
• Results for Direct CP violation
• Acknowledgement a very large fraction of these
  slides were Borrowed from our Belle colleagues.

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The Belle Experiment

• KEK the High Energy Accelerator Research
  Organisation, Tsukuba, Japan.

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The Belle detector
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Belle Collaboration
300 Physicists from 50 Institutions
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Australian Hardware Contributions

• The Silicon Vertex Detector (SVD)

Essential for 200 micron vertex resolution.
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Australian Hardware Contributions

• Constructed about 60 ladders for SVD since 2000

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Australian hardware contributions
Assembled SVD
SVD 1.1
SVD 1.2
SVD 1.4
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P violation in weak interactions

• All fermions can be expressed as a linear
  combination of left and right handed states.

The weak interaction only affects the left-handed
components. Beautifully demonstrated in pion
decay.
Weak interaction couples to left and right states
We measure exactly this!
Weak interaction couples to left only
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C violation in weak interactions

• If just re-examine the pion decay and replace all
  particles with their anti-particles.

We get a left handed anti-neutrino emerging from
the decay of of a negative pion. We dont observe
this! We only see right-handed anti-neutrinos. So
the weak interaction is not invariant under the C
operator.
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CP operation

• Notice that the combined operation works!

CP
CP is very nearly always conserved in weak
interactions
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CP violation

• CP violation is manifest in partial decay rates
  involving particles and anti-particles.
• So far only observed in Neutral K and B meson
  decays.
• Nicely demonstrated in semi-leptonic decays of
  the long-lived neutral kaon

Clear difference between matter and anti-matter.
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The Standard Model of Particle Physics.
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Flavour changing in the Standard Model

• The Standard Model accommodates CP violation via
  flavour changing weak interactions.

Mass eigenstates are not weak eigenstates.
Down type quarks are an admixture of all three
generations
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The CKM matrix.

• Letting d, s, b denote these weak eigenstate
  partners of the u, c, and t quarks, the
  coefficients can be written as the Vckm matrix

To conserve probability this matrix must be
unitary The most general 3x3 unitary matrix
allows a single complex term The Wolfenstein
parameterization shows this
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CP violation in the Standard Model

• The unitarity condition implies the relationships

One of these equations is
Mixing gives this
b?u transitions
Shown on a complex plane, this leads to the
Unitarity Triangle. Non-zero internal angles give
rise to CP-violation.
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CP violation in the Standard Model.

• Transitions between generations of quarks have
  amplitudes proportional to Vckm
• Transitions between generations of anti-quarks
  have amplitudes proportional to Vckm
• CP violation arises when these amplitudes
  interfere.
• These are generally second-order weak
  transitions.
• Still largely unexplored and a treasure-trove of
  interesting Physics.

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B meson mixing

• The and are not eigenstates of the
  weak interaction.

(CP Even)
(CP Odd)
Where p and q are approximately unity but have
different phases. These two states have slightly
different masses so their time dependence is
given by
And q and p are related to the standard model by
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B meson mixing in the Standard Model

• The transitions B0 ?anti- B0 are second order
  weak interactions.

B0 ?B0 transitions
B0 ?B0 transitions
So in the transition an extra phase factor is
acquired from
This gives a factor of
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B meson oscillations.

• The intensity is then given by

The B0 component is an initially pure B0 sample
is given by
So the intensity of and oscillate
as they decay.
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B meson mixing.

• B mesons have a mass of about 5.2 GeV.
• Yet if we plot an asymmetry ratio

Wonderful example of QM coherence! 1012
oscillations to see a single inference beat!
Recent result from Belle for B mixing.
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CP violation in the Standard Model.

• Now suppose that both and decay to
  the same CP eigenstate.

Then the mixing induces an extra phase in the
transition.
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Generic Indirect CP Measurements
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Universal Matter Anti-Matter asymmetry

• The Big Bang has matter and anti-matter created
  in equal abundance.
• But the Universe as at least 4 orders of
  magnitude more matter than anti-matter.
• There must be some interactions that favour
  matter over anti-matter
• This is CP violation.
• The Standard Model predicts CP violation in
  second-order weak interactions.
• BUT this is too weak to explain the Universal
  matter-antimatter asymmetry.
• So there must be some New Physics beyond the
  Standard Model that also provides CP violation.

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Generic Indirect CP measurements.
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Flow of analysis

• Select events which contain CP eigenstates
• Use other B to identify flavour at t 0
• Measure ??Z Z1 Z2
• Extract asymmetry
• Do cross checks
• Determine Systematic errors.

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Data Sample Worlds Best!
320 million B B events to November, 2004
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Measurement of sin(2?1)

• CP even analysis.

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ccd Sin(2?1) data 2004
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Flavour Tagging
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Multi-Dimensional Analysis

• Two Stage assignment of B-flavour.

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Wrong flavour tag fraction, w
Effective flavour tag efficiency of 28.6
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Vertexing and resolution function.

• Need to measure the distance between the two
  decays.

Check by comparing with extracted lifetimes
Use studies of J/? decays to determine the
resultion function
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Unbinned likelihood to determine sin(2?1)
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Measured Sin(2?1) (2003 data set)
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Sin(2?1) Results 2004
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The Unitarity Triangle.
Combined Belle and BaBar sin(2?1) 0.7280.037
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Looking for New Physics
b??c c s decays measure sin(2?1). Simple tree
level diagrams do not alter phase from B B mixing.
b?s s s also measure sin(2?1).
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Looking for new Physics

• b?s s s also measure sin(2?1).

Neither Vtb or Vts alter the phase obtained from
B B mixing
However now the S.M. contribution is much
reduced.
New Physics (eg new particle mass 100 GeV) could
contribute to the process altering the phase.
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B ???Ks
This is particularly true for B ???Ks where the
SM prediction is very clean. Measurements here
should give the same result as B ??J/? Ks
fKs f g KK- Ks g pp-, p0p0
Nsig 139?14 purity 0.63
purity 0.17
Nsig36?15(stat)?10(syst)
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B ???Ks
sin2f1 0.06 ?0.33 ?0.09 A 0.08
?0.22 ?0.09
Belle results to 2004
Poor tags
Good tags
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History of B ???Ks
_ sin2f1 from ccs
BABAR
Belle
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CPV for b?sss
B0 ?KK-Ks gives sin(2?1) 0.49 0.18
B0 ??Ks gives sin(2?1) 0.65 0.18
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CPV for b?sss
B0 g f0(980)Ks
sin2f1 -0.47 ?0.41 ?0.08 A -0.39
?0.27 ?0.08
Raw Asymmetry
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CPV for b?sss
B0 g wKs
Nsig 31?7 (7.3s) purity 0.56
sin2f1 0.75 ?0.64 A 0.26 ?0.48
?0.15
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Results for B0 g Ksp0
Nsig 168?16 purity 0.55
sin2f1 0.30 ?0.59 ?0.11 A -0.12
?0.20 ?0.07
Raw Asymmetry
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B0 g KsKsKs (CP-even state)
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sin2f1 from bgs penguins at FPCP04
World Average (WA)
CL 1.2 ?10-4 (3.8s)
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CPV from B??J/??0
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Note sign expected - sin(2?1)
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Sin(2?1) via B?DD modes
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sin(2?2) via B0???-
However our measurement of B0??0?0 shows there is
a significant penguin contribution
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Event Selection for B0???-
Effect of continuum suppression
(Yield for 2002 data)
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?t distributions for B???-
Direct CPV ?3.2s
App 0.58 ?0.15(stat) ?0.07(syst) Spp ?1.00
?0.21(stat) ?0.07(syst)
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Comparison with previous results.
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?3 via B?D0K
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?3 via B?D0K
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?3 via B?D0K
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?3 via B?D0K
Results for 250 fb-1
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Direct CP via B0 ?K ?-
CP in decay (DB1) weak (fk) and strong (dk)
phases, different
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Direct CP via B ?K ?0
Expect same result as B0 ?K ?-. Combined with
BaBar deviation is gt 3 ?
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Summary.

• b?ccs sin(2?1) 0.726 0.037
• B0 ?penguin s 0.41 0.07 (3.8 ?, NP?)
• B0 ? ccd early days
• B0???- sin(2?2) (140 fb-1 ) S-1.00 0.21,
  A0.58 0.15 (not confirmed by BaBar)
• B?D0K ?3 68 19
• B ?K ?- Acp -0.114 - 0.020
• Other modes and other constraints too! (B ? ??
  Arthurs work just begging to be exploited!)
• On track for another gt100 fb-1 this year
• What will we find?
• Interesting Times ?

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The Belle Experiment.

• Belle is an outstanding success
• Accumulated 320 million B anti-B decays since
  1999.
• Published over 100 journal papers and over 400
  conference contributions
• CPV paper (2001) already has more than 180
  citations.
• Lots more interesting stuff to come.