1

CP violation in B → ,

Hiro Sagawa (KEK)

FLAVOR PHYSICS & CP VIOLATION,

Ecole Polytechnique, Paris, France

on June 3-6, 2003

2

Outline

• CPCP asymmetries in asymmetries in B B00 →→ decaydecay – CP violating parameters : S and A(= C)

• Belle : hep-ex/0301032 ( to be appeared in PRD )

• BaBar : Phys. Rev. Lett. 281802

– Bound on Penguin Pollution from isospin

relation ( B→ anddecays )

• CPCP asymmetries inasymmetries in B B00 →→ decay ( decay ())– Quasi-two-body analysis

• BaBar : update at Recontres de Moriond 2003

Belle BaBar

3

Introduction

4

Introduction

B Unitarity triangle b uud

Quark mixing is described by the 3x3 Cabibbo-Kobayashi-Maskawa(CKM) matrix. (Wolfenstein parametrization)

4

1 2 31 ( )2

1 2 212

3 2(1 ) 1

( )ud us

cd cs cb

ts tb

ub

td

A i

A

A i A

V V

V V V V O

V

V

V V

1()3()

2()* * * 0ud ub cd cb td tbV V V V V V

One irreducible complex phasederives CP violation .

5

CP violation in mixing and decay

0

0

0

0

CP CPf

B

BB f

B

CPfA

CPfA

CPfA

CPfAmixing mixing

decay decay

CP

CP

CPf

ff

Aq

p A

CP violation in neutral B meson results fromthe interference between decays with and without mixing.

6

Time evolution in B0 π+π–

0

0

| |/

( ) [1 { sin( )

cos( )}]

Bt

qd

d

eP q St m t

m tA

q= +1 for B0 tag 1 for B0 tag

t=z/(c)2

2 2

2Im | | 1,

1 | | | | 1AS C

(Belle)

7

CP violation in B0 π+π–

* *

**tb td

tb td

ud ub

ud ub

V VV V

V V VV

B0

b

dB0 t t

d

b

B0

mixing

b

b

dud

B0

udW+

Tree(T)

b

dB0

duud

gt

Penguin(P)decay

22

2

0

sin(2 )

i

A

T

S

ree only

e

22

22

2

2

1 | / |, ( )

1 | / |

sin( ) , ( )

1 sin(2 ) .

i i

f

i

e

ii

f

Tree Penguin

e ee

e e

direct CP violation

C related to thru isospin ana

P

P

A

lys

T

C

S

T

A

is

8

Analysis Procedure

9

Data sampleEventSelection

Flavortagging

Vertexand t

Continuumsuppression

: charmless B decays BR ~ 10-5-10-6 : rare decays world average (10-6)

Need a lot of data

0 0

4.8 0.5

25.4 4.2

(

5.3

)

( )

( )

BR

BR

BR

Data sample Belle 85 million BB pairs BaBar 88 million BB pairs BaBar 89 million BB pairs

(HFAG table)

10

Kinematics: Reconstruction of CP side

EventSelection

Flavortagging

Vertexand t

Continuumsuppression

Kinematics

*

*

*2

*

2b beam

beamB

Bc p

Beam constrained mass

Energy d

E

ifference

EM

EE

*

*

*

:

:

:B

be m

B

a cms beam energy

cms energy of B candidate

cms momentum of B cand

E

E

p idate

Mbc(GeV/c2) E(GeV)

Signal MC

backgqq roundbackgqq round

Signal MC

K

11

Good K/ separationEventSelection

Flavortagging

Vertexand t

Continuumsuppression

Belle ACC(Aerogel Cherenkov Counter) + CDC dE/dx

For the tracks in the momentum range that covers the B0 signal, effciency = 91% 10.3% of kaons are misidentified as pions. 10.0 0.2% from K

10.6 0.2% from K+

The effect of asymmetry of this misidentification is negligible for the measurement of A and S.

Threshold type

12

Good K/ separationEventSelection

Flavortagging

Vertexand t

Continuumsuppression

BaBar DIRC (Detector of Internally Reflected Cherenkov light)

/K separation8 2

2.5

/

4 /C

C

at GeV c

at GeV c

Cherenkov angle ( , )is used separately as PDF for maximum likelihood fit.

, :C C

, :C C

Cherenkov angle for positivelyand negatively charged tracks

13

Flavor taggingEventSelection

Flavortagging

Vertexand t

Continuumsuppression

Use flavor specific

properties and correlations

14

Continuum backgroundEventSelection

Flavortagging

Vertexand t

Continuumsuppression

use kinematics and topology to separate spherical B decays from jetty qq events

15

Continuum suppression

B0 for the case of BelleCut on a likelihood ratio (LR) that combines an event topology variable (SFW) and B flight direction (cosB )

SFW: Super Fox Wolfram Fisher discriminant using modified Fox-Wolfram moments

qq

qq

qqSignal Signal

SFW cosB LR

Signal

16

Vertex reconstruction

Flavortagging

Vertexand t

Continuumsuppression

• The same algorithm as that used for sin21 meas.

• Resolution mostly determined by the tag-side vtx.

Example vertices

B0 lifetime of control sample1.5510.018(stat) ps

Time resolution (rms)1.43ps

(PDG02: 1.542±0.016 ps)

EventSelection

17

CP asymmetries in B0

18

Event reconstruction (Belle)Beam-constrained mass (Mbc) energy difference (E)

(in E signal region) (in Mbc signal region) B-candidate energy – beam energy (CMS)

K

K

other rare B decays

qq continuum

19

Fit results (Belle)

5-5 0

5-5 0 5-5 0

Large CP Violation is seen !

B0 tag B0 tag

sin term

sin term

cos term hep-ex/0301032accepted forPhys. Rev. D

0.080.07

0.77 0.27( ) 0.08( )

1.23 0.41( ) ( )

A stat syst

S stat

C

syst

LR>0.825

20

Confidence Regions (Belle)

Feldman-Cousins frequentist approach

1) Evidence for CP violationin B0 π+π–

2) “Indication” of direct CP Violation (A>0)

CL for CP conservation 3.4

21

21 12

21

2

12

2

| / | | / |

|

[sin 2 2 sin( )cos sin 2 ]/ ,

[2 sin( )sin ]/ ,

1 2 cos( )c

/ |

| / | | / |os

P T PS R

A R

T

P T

P T P TR

P T

Constraints on the CKM angle 2()

|P/T| 0.15-0.45 (representative) Theory ~0.3

1 23.5deg (=)

(Belle & BaBar combined)

2 (=) strong phase difference

78o<2<152o

(95.5%C.L.)

<0 favored

2

|P/T|=0.45

22

Constraint on -

2=78o

2=118o

2=152o1

23

Belle’s resultsof 1 and 2

are consistentwith othermeasurements.

PDG2002 + ( Belle 1 & 2 )

23

mES and E (BaBar)

-enhanced eventsPhys Rev Lett 89, 281802 (2002)

K-enhanced events

backgr dq nKq ou

backgr dq unq o

mES

mES

E

E

24

CP asymmetry result (BaBar)

Projection in signal -enhanced events

0.02 0.34 0.05

0.30 0.25 0.04

S

C

Phys Rev Lett 89, 281802 (2002)

Asy

mm

etry

E

ven

ts/1

ps

( )t ps

0B tags

0B tagqq K

0

0

0

0

( ) ( )( )

( ) ( )

sin( ) cos( )

tag

t

ta

tg

g

aga

d d

N N

N N

BAs t

t

B

Bym

S Cm m

B

t

( )C A

(A=+0.30)

25

The difference is at 2.2 level.

It’s early to say conclusively for the difference.

Fit results (Belle&BaBar)

&

26

Comparison with predictions

PQCD

A Belle BaBar PQCD QCDFhep-ex/0301032 PRL,281802

(2002)PRD67,054009 (2003)

NPB606,245 (2001)

(%) 77 27 8 30 25 4 16 ~ 30 6 12

0.30(

,

0

0.4

.23

0.18(

( )

)

),

.5(

,

)

c

purp

p

le

R lines

g

i

r

blue

k

een

n

Purple regions : PQCD favoredRegion for each 2 (60o, 100o,150o)

27

A bound on =|eff-|with an upper limit on

can constrain on using isospin relation.

2

0 0 0

2

2

: , , (limit)

: , ( 1 sin 2( ))

( , )

BRs

CP asymmetries A S A

A C

1

2A

1

2A

00A00A

0 0A A

20

00 0 0 0

0

0

00 0

0 00

( ) ( )

( ) ( )

( ) ( ) ( )

A B

A B

Amplitude for

A B

B

B

A BA

A

32ij ij

A e A

28

A bound on =|eff-|• Gronau/London/Sinha/Sinha bound (PL B514, 315 (2001))

2000

0

12

2

0

cos21 A

B BB

B B

B B

0 0 0

6

60

0 60

, ,

( 0.5) 10 ,

( 0.9) 1

4.8

0 ,

10 ,

0.48 0.1

5.6

9.

3.6

Average branching rat

B

ios

for

A

B

B

| | 48 @90% . .o C L

00 /B B

00 6(limit) 3.6 10B

(de

g)

HFAV table

29

CP asymmetries in B0

30

CP-Violating Asymmetries in B

→ ,• Principle: measure directly, even with penguins using

full Dalitz-plot analysis– difficulty

• Combinatorics and lower efficiency in three-body topology with 0

• Large backgrounds from misreconstructed signal events and other B decays

Need large statistics to extract cleanly

• “quasi-two-body” analysis:– Select the -dominated region of the K Dalitz pla

ne (Rejected when .)

– Suppression of qq backgrounds– Simultaneous fit for and

0 0 20.4 ( ), ( ) 1.3 /m m GeV c

31

0000 and BBBB

Final state : not a CP eigenstate

Basically there are four tree amplitudes:

CP Violation Study in B0 →π decay

0B

0B

0B

0B

32

B0 →π Time-dependence

Decay rate distribution ( for charge )

33

)()(

)()(

hNhN

hNhNA h

CP

)cos()(

)sin()(

tmCQC

tmSQS

dhh

dhh

direct CP violation → ACP and C = 0

indirect CP violation → S = 0

C and S are insensitive to CP violation

Time evolution includes:

Time-integrated asymmetry:

Q is the charge

K is self-tagging: 0 ,0 ,1 ,0 KKKK SSCC

Fit for:

SSCCAA KCPCP , , , , ,

34

Preliminary

The results with 89 million BB pairs @2003 Moriond EW

0.28 0.17 0.08

0.18 0.08 0.03

KA

A

qq

BR of and K

Charge asymmetry of and K

6

1.3 61.2

( ) (22.6 1.8 2.2) 10

( ) (7.3 1.3) 10

B B

B B K

B0 →π/K (BaBar) Yields and Charge Asymmetries

B0 →π B0 →K

B rel eqq at d

35

B0 →π/K (BaBar) : t distributions

B+continuumbackground

B-related background

2 (or more)from zero

36

Direct CP violation in B0 →

0 0

0 0

0 0

0 0

( ) ( )

1( ) ( )

( ) ( )

1( ) ( )

CP CP

CP

CP CP

CP

N B N B A C A CA

C A CN B N B

N B N B A C A CA

C A CN B N B

0.240.28

0.160.17

0.62 0.06

0.11 0.04

A

A

A

A (0,0)

37

Comparison with predictions

BaBar:

A = -0.18 0.08 0.03C = +0.36 0.15 0.04C = +0.28 0.19 0.04

QCDF: A = -0.015 C = 0.019 C = 0.250

w/ Charming Penguin(CP): S = -0.015 C = 0.092 C = 0.228

Phys. Rev. D67,094019, 2003

38

Prospect (B0 →π-)

L(fb) L(fb)

A

S

0.77 0.28 (

0.30 0.25 ( )

)

A

A B

BaBar

elle

1.23 0.42 (

0.02 0.34 ( )

)

S

S B

BaBar

elle

39

Prospect (B0 →π)

L(fb-1)

L(fb-1)

L(fb-1)

A

C

S

0.18 0.08A 0.36 0.18C

0.19 0.24S

40

Summary• Measurement of CP asymmetries in B0 →

• Still early to say conclusively for the difference.

• Measurement of CP asymmetries in B0 → – Quasi-two-body analysis was performed by BaBar.– Hint of Direct CPV ?

0.080.07

( )

0.77 0.27 0.08 1.23 0.41

0.30 0.25 0.04 0.02 0.34 0.05

C A S

Belle

BaBar

0.24

0.160.1

0 28

7

. 0.06

0.11 0.

0

04

.62A

A

(0,0)

2 lines

41

end