Rare B decays

BELLE

Fourth Workshop on
Mass Origin and Supersymmetry Physics

7 March 2006

Hidekazu Kakuno(Univ. of Tokyo)

Introduction: rare B-meson decays
Major B meson decays:
supressed by the CKM matrix element Vcb
For some rare B-meson decays:
Tree diagram is highly suprresed by the CKM matrix element Vub
Non-negligible contribution of the one loop (penguin) diagram
1. Decays from tree and penguin diagram-> search for the direct CP violation
2. Decays from penguin diagram-> search for the new physics that may appear in the loopb Vtb

Vts*, Vtd*

Wbc,ug,γ,ZVcb,Vub

Tree diagram

penguin diagrams,dIntroduction: Belle experimentIntegrated luminosity
Belle /KEKB accumulate
more than 500/fb data
Many exciting analysis resultsof the rare B meson decays>500/fb
357/fb386MBB
This talk includes:
1. measurement of thedirect CP Violation in B→ Kπ
2. search for b→d processes
b→dγ
B→KK
3. Forward-backward
asymmetry in B →K*llanalyses using 357/fb data

1. measurement of thedirect CP Violation in B→ Kπ

Introduction: Direct CP violation
Direct CP violation: Γ(B→f ) ≠ Γ( B→ f)
two diagrams are required to contribute to the decay
Direct CP Asymmetry:Acp=

Γ(B→f ) − Γ( B→ f)
Γ(B→f ) + Γ( B→ f)

2|A
1/A2| sin (∆φ)sin(∆δ)=
1+|A1/A2|²+2|A1/A2| cos (∆φ) cos(∆δ)
Large direct CP violation if:- the ratio of the two amplitudes |A1/A2| ~ 1- the difference of the weak phase ∆φ is large- the difference of the strong phase ∆δ is large

Introduction: B → Κ π / π πpenguin diagram and tree diagram
contribute to the decaybs,dB0,B+u, us,dK+, π+K+, π+u, ubPenguin diagram

u,u

u,u

B0,B+π+, π0d,ud,ud,uπ+, π0d,u

VubTree diagram
tree diagram is supressed by Vub

Amplitudes of Penguin and Tree diagram are comparable→ possiblity to observe a large CP violation

Analysis tools: Continuum background suppression
Major background: continuum qq events- continuum qq events- BB events(q = u, d, s, c)~1nb~ 3nbeBeq<e+B

Event topology-> Fisher discriminant
BBcontinuumqe+
B flight direction

B-Flavor tagging info.
- particle species inthe rest of the events

Analysis tools: B reconstruction
Use two variables to reconstruct B mesons from ϒ(4S) decay:∆E= Σ Ei - ECM /2
Mbc= √(ECM/2)² -|Σ pi|²

ACP(B0→K+π-)
Unbinned maximum likelihood fit to (Mbc, ∆E) distribution0B

systprelimstat

5.0σ

600

2700

Entries/2MeV/cin-0.113±0.022±0.008

Entries/2MeV/car

ACP(B0→K+π-) =y2

Signal yields: 3026 ± 53− +K π

500400300700
6004003002001001005.255.3+ −K π

50020005.2B05.25.252

ACP=-0.113±0.022±0.008(4.2σ; PRL 93, 131801(2004))

600− +K π500

Mbc (GeV/c )Entries/20MeV

Entries/20MeV

consistent with the value
reported by BaBar:

700400300700
600

400
300
200

100

10000.5∆E (GeV)+ −K π50020005.32

Mbc (GeV/c )(including syst. uncertainty)

0000.5∆E (GeV)hepex/0507045

ACP(B+→K+π0)

3.1σ difference from
A (B0→K+π-)
CPpuzzling

Entries/2MeV/c2prNo DCPV observed

B200Kπ- 0

175150150125125100

1007575505025250
5.2

5.250
5.2

5.32100

CP20

5.3

Mbc (GeV/c )
100

K-π0

80

0

5.25

2

Mbc (GeV/c )Naive expectation from SM:
60
A (B0→K+π-) ~ A (B+→K+π0) 40
CP+K+π0175

Entries/15MeV

elim+0.04±0.04±0.02

Entries/2MeV/c2inar

ACP

200

Entries/15MeV(B+→K+π0) =yB-K+π0806040
20-0.25

00.25∆E (GeV)0-0.2500.25∆E (GeV)2. search for b→d process
b→dγ
B→KKIntroduction: search for b→db→d transition- loop diagram -> sensitive to the new physics- highly suppressed compared to the b→s transition(|Vtd/Vts|² ~ 1/100)
the decay modes with pure b→d processes:
posibility to observe the CP violation through theinterference between SM and NP processes in the loop
increase of
the integrated luminosity

decays with pure b→d processes
become accesible!

b Vtb

Vtd*

g,γ,Zdb->d γpure b→d (radiative penguin) process
Strong supression from Vtd-> sensitive to the new physics

γb- also important for theconstraint on a CKM matrix element |Vtd| B0,B+  ρ,ω d,u !"$#Wd   whereVtd  % (Isospin relation)

&%'"(#%,)+*  *', - .("-d,u

B->d γ : result
14B →ργ-2-

Entries/(4 MeV/c )Entries/(50 MeV)

121086420-0.4-0.2

00.2

128642
5.22 5.24 5.26 5.28

0

B → ρ0γ

12108642-0.4-0.20142

1400.20121∆ E (GeV)

8 9:<; =&>&?6363@@GA.F0B0C ?*6363@@6D6HC
EE

2.6σ

combined

6I

42

2

Entries/(4 MeV/c )Entries/(50 MeV)

20.2

5 6 7

85305.1σ

5.22

5.24

5.26

5.28

5.3

J

KMLONQP RSTVUXW Y[Z\\]]^`bd__DZ\3\3]e]a^bf\bcc

Mbc (GeV/c )0-0.2$&%'$ ( )*++,.,3-2 )*++0/04
112

B → ωγ-0.4"#100
5.2

0.4

401.5σ!

5.3

B → ρ 0γ

∆ E (GeV)
5 Mbc (GeV/c )Entries/(4 MeV/c )Entries/(50 MeV)

16 BR(x10-6 )

2∆ E (GeV)
18

386MBB  

1005.20.4

B- → ρ-γ

0.40

B → ωγObservation ofthe b→dγ process

432
10
5.2

5.22

5.24

5.26

5.28
2

Mbc (GeV/c )

5.3

5.5σ

Constraint on the CKM matrix element |Vtd/Vts|form factor ratioeffect of SU3 breaking exp.



theory0.143 < |Vtd/Vts| < 0.260 @95%CL

constraint on theunitarity triangle (incl. BaBarB-> KK









decayspure b→d processstrong suppression by Vtd -> sensitive to the new physics


decays

W exchange, final state interaction, ...
vary small branching fraction is expectedWbVtdd
K0u

bss

B0,B+

W

B0s

s

K0,K+d,uK+d,uduK-Entries/20MeV

Entries/2MeV/c2B-> KK: result
1816
141210386MBB

25

20

K+K-        !  !  " #%$ & " # ' & " #)(158106
4BR(x10-6 )

  

0.5σ

52
0
5.2

5.22

5.24

5.26

5.28

0-0.3

5.3

2

12

Entries/20MeV

Entries/2MeV/c2

Mbc(GeV/c )

10
8

-0.2

-0.1

00.1

0.2

0.3

∆E(GeV)      

12

K0K+

10
8

66442

205.2

5.22

5.24

5.26

5.28

5.3

0-0.3

2

Entries/2MeV/c2Entries/20MeV

Mbc(GeV/c )141210812-0.2

-0.1

00.1

0.2

0.3

∆E(GeV)3σ evidence for
K0K+ and K0K0K0K0108664
4220
5.2

5.22

5.24

5.26

5.28

5.3
2

Mbc(GeV/c )

3.0σ

0-0.3

-0.2

-0.1

00.1

0.2

0.3

∆E(GeV)

red: signal
green: B->Kπ BG

3.5σ

3. Forward-Backward asymmetry in
B →K*llAFB in B->K*ll: Introduction
B→K*ll: Sensitive to the Wilson coefficients C7, C9 and C10A7(q² independent term of C7): |A7| is constrained by B→Xsγ
sign of A7? A9,A10 values?
new measurement AFB(Forward-Backward Asymmetry)

AFB

forwardbackward
Γ(forward)−Γ(backward)
AFB=
Γ(forward)+Γ(backward)
determine the relative sign between A7 and A10, and between A9 and A10
1
A10/A7SM (A =-0.330, A =4.069, A =-4.213)
0.8
SM
A9/A7
(Ai: q² independent term of Ci)

0.6
0.4
0.2
0-0.2
-0.4
-0.6
-0.8
-1

7

910A7A10 sign flipped caseboth A7A10 and A9A10 signs flipped case
A9A10 sign flipped case02468101214162q18202 2GeV /cB->K*ll events
Events / 2.0 MeV/c2386M BB30

N(B→K*ll) = 114±14 (purity 44%)(a) K e e++ -(b) K* e e+ -(c) K+ µ+µ-(d) K* µ+µ-(e) K+ l+l-(f) K* l+l-

20

N(B→Kll) = 96±12 (purity 57%)
10(B→Kll: used for the null asymmetry test)
030
20Maximum Likelihood fit tonormalized double differential
decay width (1/Γ)d²Γ/dsdcosθ
(s=q², θ: angle between l- and B)

1006040
20

constrain A9/A7 and A10/A705.2 5.225 5.25 5.275 5.2 5.225 5.25 5.275 5.32Mbc (GeV/c )A10/A7AFB (bkg-sub)

AFB in B->K*ll
1(a) negative A740

0.5
2000+ + --0.5(a) K l l-20-1
0

2.5

5

7.5

10

12.5

15

17.5

20 22.5 25
22 2q GeV /c

AFB (bkg-sub)null asymmetry test-40-40-2002040
A9/A7

Best fit for negative A7(SM like)A9/A7=-15.3 +3.4-4.8 ±1.1
A10/A7=10.3+5.2-3.5 ±1.8

10.50* + --0.5

K l l
negative A7-102468101214162q18202 2
GeV /cc.f. SM: A9/A7 = -12.3,A10/A7 = +12.8
sign-flipped A9A10 is excluded
at 95%CL
sign of A7A10 is not determined(need more data)SummaryImproved measurements- Acp in B→ Kπ decays
Obvervation of the Direct CP violation in B0→K+π-New measurements- search for b→d process
Observation of the b→d γ decay+0Evidence of B →K0K+ and B →K0K0- meaurement of the forward-backward asymmetry in B→K*ll
important tools for probing the new physics beyond the SM
Many other analyses that are not covered in this talk:Acp measurements for many other rare B decays,
polalization measurements in B→ VV decays, ...