CP Violation from B-factories

Hiro AiharaUniversity of Tokyo

2006 Aspen Winter Conference ‘‘Particle Physics at the Verge of Discovery’’

- Results from BaBar and Belle -

Why (still) flavor physics ?

• If New Physics at TeV, it might manifestitself in flavor physics at B-factories via CPVin B /D, rare B/D and rare tau decays.• If it does not show up, we still want to know why.

• What is the role of measurements of Bmeson system in this context ?

• In particular, CKM angle measurements.

2

*

ud ubV V

*

td tbV V

2 ( )! "

1 ( )! "3 ( )! "*

cd cbV V!

2! = measured as phase difference between

B0 " B0

" f and B0 " f

decay paths.

Measured in tree and loop processes.

Loop probes New Physics.

! = measured as phase difference between

b" u and b" c transitions

Mesaured in tree-level processes,

and therefore insensitive to

New Physics.

! " # $ % $ &

= & measured with mixing (%)

d s b

u

c

t

1 1 e! i"

1 1 1

e! i#

1 1

$

%

&&&

'

(

)))

3

I.II.

III.

�

VudV

ub

*+V

cdVcb

*+V

tdVtb

*= 0

phases in CKM

sin2! : tree vs loop

B0

B0 B

+ +

!

!

K0

K0

V

td

*

V

td

*

V

td

*

V

td

*

!"

!"

Unless threre is a new phase(s) in a loop,

measurements of mixing-induced CP violation

should give the same sin2!.

B0

B0

B0

4

Belle 2005 update : BBelle 2005 update : B00 J/J/ψψ KK00 w/386 M BB pairs w/386 M BB pairs

2*

/

2*

KsJbeambcPEM !"=

B0 J/ψ KS B0 J/ψ KL

Nsig = 5264Purity 98 %

CP odd Nsig = 4792Purity 60 %

CP even

0 0

__

5

! B0 ("t) # f( ) $ ! B0 ("t) # f( )

! B0 ("t) # f( ) + ! B0 ("t) # f( )= Dsin2% sin("m

d"t)

sin2! = 0.652 ± 0.039 ± 0.020

6

hep-ex/0507037

7HFAG=Heavy Flavor Averaging Group

! = 68! solution is disfavored >2"( )by

• Time dependent angular analysis of B0 # J /$ K*0 (BaBar)

• Time dependent Dalitz analysis of B0 # D0% 0 (Belle) 8

Loops: How New Physics contributes to bs

0B

!"

b ss

s

d

d

+W

g

, ,u c t

“Internal Penguin”

!

K

0

!"0 0 B K

!"#0 0 B K

!

0

SK

0B

b

s

s

s

d d

!"

0

SK

0B

b

s

s

s

d d

Many new phases arepossible in SUSY

New physics in loops?

Gluino-squark loop dominates.

! sin2" can be significant (~0.2 or more).

“Compelling Evidence” for CP Violation in a bs mode

830±35

! B0 ("t) # f( ) $ ! B0 ("t) # f( )

! B0 ("t) # f( ) + ! B0 ("t) # f( )= Dsin2% sin("m

d"t)

Belle 386M BB pairs

10

Almost all are systematically

below the sin(2β) value

from BJ/ψ K0 modes

(Belle data: hep-ex/0507037)

11

New Physics ??

Very large effects of order unity, ΔS~1,are now ruled out.

Theory corrections aresmall and opposite in signto the exp deviations.

(Deviation from Bψ K0 result)

A minimum of 1000 fb-1 / each experiment

is required.

12

*

ud ubV V *

td tbV V

! ("

3)

*

cd cbV V!

Tree-level processes are immune toNew Physics.

A(B+ ! D

0K

+) = A

BrBei " +#3( )

A(B+! D

0K

+) = A

B

γ=φ3

rB= suppression due to Cabibbo and color matching = 0.1~0.2δ = strong phase

D0 &D0 can decay to the same final state K

S

0! +! " .

The interference of the above amplitudes gives # 3.

The sensitivity to φ3 is proportional to rB.

A(B!" D

0K

!) = A

BA(B

! " D0K

!) = A

BrBei # !$3( )

14

This final state arises from Vus

suppressed and Vub

suppressed diagrams.

Dalitz analysis

B+:

B-:

m+=m(Ksπ+), m−=m(Ksπ−)

r

r |A2||A1|

r =

2m

!

2m

+

0 D 2

m!

2m

+

0 D obtain

fromtagged D0

(D*+→ D0π+)sample

Decay amplitudes

To extract !3," and r, we need to know f (m+

2,m#

2), Dalitz distribution of D$ KS%

+% #.

Density of Dalitz plot distribution isproportional to |Amplitude|2.

B+/−→D0K+/−: KS π+π- Dalitz plot distributions

B+→D0K+ B−→D0K−

B+→D0K+ B−→D0K−

Differences between B+ and B− signifies direct CP violation.Above, D0 is super-position of D0 and D0

227M

275M

139evts 137evts

282evts

PRL 95 (2005) 121802

[hep-ex/0411049,0504013]

φ3 = 63 ± deg.1512

(Non-trivial constraint)

! "

3 results

17

*

ud ubV V

*

td tbV V

2 ( )! "

*

cd cbV V!

! " # $ % $ &

= & measured with mixing (%)

Asym = S sin !md!t( ) + A(= "C)cos !md!t( )

CP Violation in B0 ! "+"# and $ +$ # (Charmless two-body decays)

!("2 )eff is shifted from !("2 ) due to loops (aka penguin pollution).

VV final state is a mixture of CP eigenstates, while # +# $ is CP even.

%% could be less sensitive to (or more diffcult to extract) !.19

!t = decay time interval of two B mesons

Miracles in B0 ! "+"#

1. Penguin contribution turns out to be small.

Br B0 ! "0"0( ) < 1.1#10

$6(90%C.L.) ! Br B

0 ! "+"$( ),Br B+ ! "+"0( )

" 30 #10$6BaBar PRL94, 131801(2005)

! eff "! < 14

!

90%C.L.( )

20

Gronau-London, PRL 65 3381 (1990)

small Penguin pollution (θ ) 2θA00

A+0

A+-/ 2

! eff "! < 35

!

90%C.L.( ) for B0#$

+$

"

2. turns out to be fully polarized longitudinally.!! final state

Angular analysis shows a longitudinal fraction of the final state to be

The longitudinally polarized state is a CP even eigenstate.21

BaBar fL= 0.978 ± 0.014

!0.029

+0.021

Belle fL= 0.941

!0.040

+0.034± 0.030

PRL95,041805 (2005)

hep-ex/0601024

0B

! +

! " 0!0

!

!"

!+

0, 1!" = ±

232 M B0 tags

Δt (ps)

B0 tags

BABAR, PRL 95, 041805 (2005)

Measurement of CP asymmetry for Bρ+ρ−

BaBar Belle

S!!

"0.33± 0.24"0.14

+0.080.08 ± 0.41± 0.09

C!!

"0.03± 0.18 ± 0.09 0.00 ± 0.30 ± 0.09

S!!= 1" C

!!

2sin 2#

eff( )

22

Belle Constraints on Belle Constraints on φφ2 2 ((αα))

Bππ PRL 95, 10801 (2005) & ρρ combinedBρρ onlyhep-ex/0601024

!2(" ) = (88 ±17)!

59! < !2< 115! (90%C.L.)

!2(" ) = (93

#11

+12 )!

75! < !2< 113! (90%C.L.)

24 No !" yet # mirror solution is still allowed.

!("2)!

W.A. 98.6-8.1

+12.6

Indirect 97-19

+13

All W.A. 98.1-7.0

+6.3

BaBar 232M pairsBelle 275M pairs

!! yields the best ".

!# helps to remove mirror solution.

## has limited sensitivity.

Good agreement with indirect constraints. 25

In conclusion

The CKM Triangle Using Angles Only

! = 21.7"1.2

+1.3

# = 63"12

+15

$ % " ! " # = 95.3"12

+15

&(' % " ! " # ) = 98.6"8.1

+12.6

good agreement

27

28

!"= sin2# "K

0 $ sin2# J /% K0= $0.22 ± 0.19

!&= sin2# '& K

0 $ sin2# J /% K0= $0.21± 0.09

Belle 350 fb-1 + BaBar 240 fb-1

(Summer 2005)

1000fb-1 for each collaboration brings the error of !

" down to 0.04.

2005 results

550fb-1

320fb-1

29

Integrated luminosity of Belle and BaBar

Belle

BaBar

date

End