Transcript CP VIOLATION (B-factories)

CP VIOLATION (B-factories)
P. Pakhlov (ITEP)
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 2β
cos 2β
εK
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.
*
VudVub

    Arg 
* 
 VtdVtb 
α
VtdV*tb
VudV*ub
VcdVcb* 
  Arg 
* 
V
V
 ud ub 
sin2β:
γ
β
VcdVcb* 
  Arg 
* 
 VtdVtb 
experimentally
easy
VcdV*cb
b  cc s : Bd  J /Ks0 , Bd  J /KL0 , Bd  J /K *0
b  cc d : Bd  DD , Bd  DD * , Bd  D*D , Bd  D*D *
b  sss, dds : Bd   0 Ks0 , Bd  Ks0
sin2α:
b  udd : Bd   0 0 , Bd     , Bd      , Bd   0 0
sin2γ:
b  cs u : B  DK
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 α
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B0  π π
Vub
b
d
d π–
u
u +
π
d
A VubVud*
 *
A VubVud
In this case the penguin diagram
is not small and has different
weak phase:
• The indirect CP violation
~ S sin(Δm t), where S≠ sin 2α,
but sin(2α + some not-negligible
phase).
• There will be direct CP
asymmetry ~ A cos(Δm t),
b
d
V*td
t
d
π–
u
u +
π
d
How to take into account this?
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B0  π π

The decay amplitudes B → π+π– (ρ+ρ–) are characterized by
two different CKM terms:


a tree term (T) ~ Vub* Vud (dominant)
a penguin term (P) ~ Vtb* Vtd, (suppressed, but not small)
0
ACP ( t ) 

N ( B 0     )  N ( B     )
0
N (B    )  N (B    )
0




 S  sin(mt )  A  cos(mt )
Parameter S of indirect CPV:
S  sin 2  2r cos sin(   ) cos2  O(r 2 )
δ – the relative strong phase between T and P amplitudes.
r < 1 – ratio of P to T amplitude

We can measure effective α (αeff) shifted by extra angle
S  1  C 2 sin(2eff )
But we want α!
Additional inputs required.
eff    
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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 BR’s of B0 and B+ to ππ decays: π+π–, π0π0, π+π0.
 To extract θ build two triangles:

1
A 
2
2αeff
A00
1
A 
2
A00
A0
2α
A0
Isospin triangles
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B0  π+ π–: experimental results
Phys.Rev.Lett., 98, 211801(2007)
B0 tag
_
B0 tag
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  ρ+ρ–: experimental results
Angular analysis: purely CP=+1 final state
Small
Br(B0

ρ0ρ0 ):
 
A+
+
small penguin contribution
+
S = 0.19 ± 0.30 ± 0.07
A = 0.16 ± 0.21 ± 0.07
A0
A-
S = –0.17 ± 0.20 ± 0.06
A = –0.01 ± 0.15 ± 0.06
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Fit results
Add also B0  ρ±π±: (not
CP eigenstate, but B0 can
decay to both ρ+π– and ρ– π+)
r(π+π– )> r(ρ+π– )~r(ρ– π+)>r(ρ– ρ+ )
  (8944..42 )
68% C.L. interval
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Angle γ
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Direct CPV and γ
B→DK
Vud
V*

ub
Aλ3

V*ub
b
c
s
u

VcdV*cb
u
u
Color suppressed
D0
K–
VtdV*tb
Aλ3(ρ+iη)
u
V*cb
s
b
c
u
u
K–
D0
Color allowed
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The angle between two amplitudes is really γ, but the
final states are different D0≠D0 , however …
D0 decays into CP eigenstate (rarely – Cabibbo suppressed
modes, e.g. K+K–, KSπ0)
GLW method. Phys. Lett. B253, 483 (1991)
D0 decays into final state typical for D0 (very rarely – Doubly
Cabibbo suppressed modes, e.g. K+ π–). 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. KSπ+ π–): 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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γ from GLS and ADS methods
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γ from GGSZ method
Measure B+/B– asymmetry across Dalitz plot
A  f m2 , m2   rB ei ei f m2 , m2 
Mirror symmetry between
D0 and D0 Dalitz plots
Determine f in flavor-tagged D*+→D0π+ decays
x± = rB cos( δ ± γ ) , y± = rB sin( δ ± γ )
2γ
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Fit to all
measurements
  (7319
24 )
68% C.L. interval
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
(ρ,η)
*
Vud* Vub
phase of
Vub
2 
phase of
Vtd
1 
3 
0
Vtd Vtb
Vcd* Vcb
1
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Testing loops!
V*
b
d
ts
t
A VtbVts* VcbVcs*
 *  *
A VtbVts VcbVcs
s
φ
CP asymmetry should be ~ sin2β
s
No tree contribution!
s
K0 Theoretical uncertainty ~ 0.01-0.03
much smaller than the current exp error!
d
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)
b
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!
d
?
?*
?
?*
s
φ
s
s
K0
d
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Sin 2β from penguin decays
2005 intrigue: penguin CP violation
parameter was ~3σ smaller than sin2β
1.9 σ
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 γ
polarizations for B0 and B0
γ
b
d
t
s
d
K*0
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
Bl- K(*)
B
Bl-
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Br(B → Xs γ)
W–, H–
To reduce model uncertainty need to
measure at as smaller E as posible
b
d
t
γ
s
d
Xs
S/B~1
S/B~200
S/B~20
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Purely leptonic decay
b
u
W–
τ
υ
b
u
H–
~mb tanβ
τ
υ
~mτ
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 Δmd
WA experiment – expectation ~ 2.4 σ difference!
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Loops in B vs direct searches
Atlas 30 fb–1
Atlas
1fb–1
95% excluded
by CDF
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KEKB/Belle
Two super B-factory projects
are prolongation of the successful B-factories
PEP-II/BaBar
8 × 1035
2.1 × 1034
10 ×
1035
1.2 × 1034
SuperB
SuperKEKB/Belle2
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Physics reach with 50 ab–1 (~ 5 years with 8×1035/cm2/s)
Which physics will we do at Super B-factories?
Basically the same we did at B-factories:


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




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 ΔS σ ≈ 0.02–0.03 for B → K0 
(K0 η').
search for CPV in radiative decays B → K*0(KS0 π0) γ
is a test of right-handed current in the penguin loop
(CPV ≠ 0).
Rare decays b → sg(γ), B → τν. Even Br’s constrain
mass of NP (provided CKM matrix elements and FF
are known precisely).
Electro-weak penguins b → sμμ, see, sνν: Br’s, Q2 distribution, FB asymmetry are sensitive to NP
+ many new decay channels hardly / not seen with
the present statistics.
+ New ideas.
50ab-1
B0→ K0
ΔS=0.23
B0→J/ψK0
Not technical updates of the previous analyses:
need to reduce model dependence and systematic uncertainties
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