CP VIOLATION (B-factories)

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CP VIOLATION (B-factories)

• P. Pakhlov (ITEP)

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Previous lecture

• 10 years of running of two B-factories provided
  high statistics (109 B0 one year of operation
  of LHCb). We have measured CP violation in B0 ?
  J/? K0 quite precisely.

Summary of CP violation measurements (discussed
yesterday)
sin 2ß
cos 2ß
eK
Do allowed areas have intersection? Does this
mean that KM ansatz is checked?
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The UT constrain
- One way to test the Standard Model is to
measure 3 angles and check if the triangles
closes. - This is not yet all possibilities. We
can measure 3 sides and check the consistency
with angle measurements.
experimentally easy
sin2ß
sin2a
sin2?
hard
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Combine all measurements together

• It is done now at professional level few
  competing averaging groups make fits of all
  available data.
• They publish report and even papers. In the
  nearest future averaging groups, rather
  experimentalists will make new discoveries,
  manipulating with experimental measurements.
• However, they do useful job
• Somebody needs to read 300 papers by Belle and
  BaBar and summarizes the results.
• They calculate WA, taking into account common and
  individual errors of experiments.
• They check the consistency.
• They produce good pictures, representing the
  results.

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Angle a
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B0 ? p p

• In this case the penguin diagram is not small and
  has different weak phase
• The indirect CP violation
• S sin(?m t), where S? sin 2a, but sin(2a
  some not-negligible phase).
• There will be direct CP asymmetry A cos(?m t),

How to take into account this?
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B0 ? p p

• The decay amplitudes B ? pp (??) are
  characterized by two different CKM terms
• a tree term (T) Vub Vud (dominant)
• a penguin term (P) Vtb Vtd, (suppressed, but
  not small)
• Parameter S of indirect CPV
• d the relative strong phase between T and P
  amplitudes.
• r lt 1 ratio of P to T amplitude
• We can measure effective a (aeff) shifted by
  extra angle
• But we want a!
• Additional inputs required.

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Isospin triangles
Gronau-London idea

• The cleanest method now available is the isospin
  analysis, proposed by M. Gronau and D. London. We
  need to measure all 6 BRs of B0 and B to pp
  decays pp, p0p0, pp0.
• To extract ? build two triangles

2aeff
2a
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B0 ? p p experimental results
Phys.Rev.Lett., 98, 211801(2007)
S 0.61 0.10 0.04 A 0.55 0.08 0.05
S 0.68 0.10 0.03 A 0.25 0.08 0.02
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B0 ? ?? experimental results
Angular analysis purely CP1 final state
Small Br(B0 ? ?0?0 ) small penguin contribution
S 0.17 0.20 0.06 A 0.01 0.15 0.06
S 0.19 0.30 0.07 A 0.16 0.21 0.07
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Fit results
Add also B0 ? ?p (not CP eigenstate, but B0
can decay to both ?p and ? p)
r(pp )gt r(?p )r(? p)gtr(? ? )
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Angle ?
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Direct CPV and ?
B?DK
A?3
Vub
A?3(?i?)
Vcb
Color suppressed
Color allowed
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The angle between two amplitudes is really ?, but
the final states are different D0?D0 , however
D0 decays into CP eigenstate (rarely Cabibbo
suppressed modes, e.g. KK, KSp0) GLW method.
Phys. Lett. B253, 483 (1991)
D0 decays into final state typical for D0 (very
rarely Doubly Cabibbo suppressed modes, e.g. K
p). Enhance CP asymmetry by suppression (in
D-decay) of allowed (in B-decays) ADS method.
Phys. Rev. Lett. 78, 3357 (1997)
D0 decays into three body state (e.g. KSp p)
mixture of opposite CP eigenvalues 1/1, also
contain DCSD. Resolve by Dalitz analysis. GGSZ
method. Phys. Rev. D68. 054018 (2003) (Used by
experimentalists (A.Bondar) before suggested by
theoreticians)
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? from GLS and ADS methods
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? from GGSZ method
Mirror symmetry between D0 and D0 Dalitz plots
Measure B/B asymmetry across Dalitz plot
Determine f in flavor-tagged D?D0p decays
x rB cos( d ? ) , y rB sin( d ? )
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Fit to all measurements
The accuracy of present measurements are limited
by statistics (we really study VERY rare decay).
The systematics and model uncertainties are much
smaller.
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Sides of UT
(?,?)
?2
(a)
phase of Vtd
?1
?3
(g)
(b)
phase of Vub
0
1
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(No Transcript)
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Testing loops!
CP asymmetry should be sin2ß
No tree contribution!
Theoretical uncertainty 0.01-0.03 much
smaller than the current exp error!
All our previous measurements test new physics
contribution to the box diagram and check the
consistency with pure tree (where no big
contribution from NP expected) This one really
give access to the loop. If any (heavy) particles
(with extra to KM phases) are involved in the
loop we can see the effect!
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Sin 2ß from penguin decays
2005 intrigue penguin CP violation parameter was
3s smaller than sin2ß
1.9 s difference

Precision of measurement (10) is dominated by
statistics
To obtain sensitivity 1-2, need few years of
LHCb or SuperB-factory data taking.
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Test of V-A in the loop
Indirect CP violation No indirect CP asymmetry
expected in SM different ? polarizations for B0
and B0
B?K(KS?0) ? use KS secondary tracks to
reconstruct B vertex
The present measurements (accuracy 0.2) are far
from the real test of V-A in the penguin loop.
Good task for SuperB factory with L 100 times
higher than at B-factories
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Electroweak penguin FB asymmetry
B
K()
?Bl-


l l
?Bl-
Wilson coefficients
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Br(B ? Xs ?)
To reduce model uncertainty need to measure at as
smaller E as posible
S/B1
S/B200
S/B20
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Purely leptonic decay
mb tanß
mt
Reconstruct B fully, see one track from decay,
check that there is no extra energy deposition in
the event
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Compare with SM constrain on charged Higgs
Theoretical uncertainty due to fB and Vub are
reduced by using prices measurement of ?md
WA experiment expectation 2.4 s difference!
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Loops in B vs direct searches
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Two super B-factory projects
KEKB/Belle
PEP-II/BaBar
are prolongation of the successful B-factories
SuperB
SuperKEKB/Belle2
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Physics reach with 50 ab1 ( 5 years with
81035/cm2/s)
50ab-1

• Which physics will we do at Super B-factories?
• Basically the same we did at B-factories
• Measure UT (angles sides) with much better
  precision. If new phases contribute to any
  measurable ? inconsistency of UT.
• CPV in b ? sqq vs b ? ccs Extra new phases in
  the penguin loop makes CPV parameters different.
  Typical accuracy in ?S s 0.020.03 for B ? K0 ?
  (K0 ?').
• search for CPV in radiative decays B ? K0(KS0
  p0) ? is a test of right-handed current in the
  penguin loop (CPV ? 0).
• Rare decays b ? sg(?), B ? t?. Even Brs
  constrain mass of NP (provided CKM matrix
  elements and FF are known precisely).
• Electro-weak penguins b ? sµµ, see, s?? Brs, Q2
  -distribution, FB asymmetry are sensitive to NP
• many new decay channels hardly / not seen with
  the present statistics.
• New ideas.

B0? ?K0
?S0.23
B0?J/?K0
Not technical updates of the previous analyses
need to reduce model dependence and systematic
uncertainties