Measurements of the angle : , (BaBar & Belle results) Georges Vasseur WIN`05, Delphi June 8, 2005.

Measurements of the angle : , (BaBar & Belle results)

Georges Vasseur

WIN`05, Delphi

June 8, 2005

June 8, 2005 Georges Vasseur 2

Outline

• Physics motivation

• Measurement of in B→

• Measurement of in B→ Dalitz.

• Summary on .


CP violation

• CP violation is explained in the Standard Model by a phase in the CKM unitary matrix.

• In the Wolfenstein parameterization:

with0.22 , A 0.83• CP violation if ≠ 0.

1)1(

1

)(1

23

22

32

2

2

AiA

A

iA

VVV

VVV

VVV

V

tbtstd

cbcscd

ubusud

CKM


The unitarity triangle

= process involving both B0 mixing and b→u transition

0*** tbtdcbcdubud VVVVVV 0*** tbtdcbcdubud VVVVVV

(0,0) (0,1)

Vub Vud* Vtd Vtb*

VcdV*cbVcd Vcb*

= phase of Vtd (B0 mixing)

= phase of Vub (b→u transition)


CP violation in the interference between mixing and decay

• For a CP final state fCP, time-dependent asymmetry is:

• With

)cos()sin(

)()(

)()()(

00

00

tmCtmS

fBfB

fBfBtA

dfdf

CPCP

CPCPf

CPCP

CP

C 0 : Direct CP violation

CP

CP

CP

f

ff A

A

p

q21

)(2

CP

CP

CP

f

ffS

2

2

1

1

CP

CP

CP

f

ffC

S 0 : Indirect CP violation

FinalStateAmplitudes

00

00

BqBpB

BqBpB

H

L

from mixing

B0

B0

fCP

Mixing (q/p) CPfA

CPfA


CP violation in B0→ρ+ρ-

• I

• Access to from the interference of a b→u decay () with B0B0 mixing ().

d

d

0B

*tbV

tdV

b

b

0Bt

t

*tdV

tbV** // tdtbtdtb VVVVpq

B0B0 mixing

du

dd0B

ubV

*udV

b u

Tree decay

ubudVVA *

sin

)2sin(1 2

C

CS eff

ii

iii

eePT

eePTe

2

du

dd

0B

g

b

utcu ,,

Penguin decay

tbtdVVA *

Inc. penguin contribution

0

)2sin(

C

S

222 iii eeeA

A

p

q

How can we obtain α from αeff ?

T = tree amplitude P = penguin amplitude = strong phase difference between penguin and tree

Tree only Tree + Penguin


Isospin analysis• Use SU(2) to relate amplitudes of all modes.

Gronau, London : PRL65, 3381 (1990)Gronau, London : PRL65, 3381 (1990)

)( 0 BAΑ

)( 00000 BAΑ

)( 00 BAΑ

Small amplitudes

2| eff

| )(~ 0 BAΑ

)(~ 00000 BAΑ

000000 ~

2

~~

2

ΑΑ

ΑΑΑΑ


Asymmetry measurement

• Exclusive B meson reconstruction.• Time measurement: z ≈ 250 m, z ≈ 170 m.• B-flavor tagging: Q = (1-2)2 ≈ 30%.

– with efficiency and mistag rate.

t =0

(4S)

tagB 0l (e-, -)

z = t c

fully reconstructed B

B 0Coherent B0B0

production


Common features of the analyses

• Kinematical signal identification with– Beam energy substituted mass– Energy difference

• Hadron ID (separation /K).• Event-shape variables combined in a neural

network (NN) or Fisher discriminant to suppress jet-like continuum event.

2*2*BbeamES pEm

**beamB EEE


B0→ρ+ρ- analysisB→B→ρρ++ρρ-- not historically favored for measuring α:

2 π0s in the final state.

3 amplitudes (VV decay): A0 (CP-even longitudinal), A|| (CP-even transverse), A┴ (CP-odd transverse).

But turned out to be the best mode:

Large branching fraction.

Penguin pollution much smaller than in B→ππ.

~100% longitudinally polarized! Pure CP-even state.

2

21

22

21

2

21

2

coscossinsin14

1

4

9

coscos

1 LL ff

dd

d

021.0029.0014.0978.0)(

Lf

BaBarBaBar

PreliminaryPreliminary

signal

bkgd

BaBar, hep-ex/050349, submitted to PRL

)89( 10)5430()( 60BBMBB

BaBar, Phys.Rev.Lett 93, 231801 (2004)

232 MBB


Details of the B0→ρ+ρ- analysis

• Unbinned extended maximum likelihood fit on a data sample of 68703 events.

• Efficiency on signal: 7.7%.• 8 observables: mES, E, t, NN, m (x2), cos

hel (x2).

• Modelisation of signal (1% of fit sample), continuum (92% of fit sample), and 38 different modes of B-background (7% of fit sample).

• Extract signal yield, longitudinal polarization fraction, cosine and sine coefficients.

232 MBB


ACP(t) in B0 decays

tags0B

tags0BPreliminaryPreliminary

09.018.003.0

24.033.0

52617)(08.014.0

long

long

C

S

BN


signal

bkgd

232 MBB


B+→ρ+ρ0 analysis

• For isospin analysis, need other B→ rates.

• B+→ρ+ρ0 was measured two years ago by both BaBar and Belle.

04.097.0)(

10)8.55.22()(

:BaBar

003.0007.0

0

67.54.5

0

Lf

BB

02.011.095.0)(

10)1.77.31()(

:Belle

0

68.37.6

0

Lf

BB

Phys.Rev.Lett 91, 171802 (2003) Phys.Rev.Lett 91, 221801 (2003)

89 MBB 85 MBB

005.0007.0

060 96.0)( 10)4.64.26()( :average World

LfBB


B0→ρ0ρ0 analysis

• Limiting factor in the isospin analysis.

• Tree is color suppressed.• No significant signal:

– Penguin are smalls.

• Dominant systematic comes from the potential interference from B→a1

±± (~22%).1233)( 22

20000

BN

C.L.%90101.1

10)19.054.0()(6

636.032.0

000

BB

)M227( BB

%27Eff.Rec.

BaBar, Phys.Rev.Lett 94, 131801 (2005)


Isospin analysis with B→ρρ

)%90(101.1)(

10)4.64.26()(

10)5430()(

6000

60

60

CLBBF

BBF

BBF

Phys.Rev.Lett 94, 131801 (2005)

Phys.Rev.Lett 91, 171802 (2003) Phys.Rev.Lett 91, 221801 (2003)

Phys.Rev.Lett 93, 231801 (2004)

|eff |< 11°

]123,79[:range %90

13100

CL


Error dominated by measurement


B0→(ρ)0 analysis• Unlike , is not a CP eigenstate

– Must consider 4 configurations– Equivalent "isospin analysis" not viable.

• However, a full time-dependent Dalitz plot analysis can constrain

0B 0B

0B 0B

–+

+–00

Snyder, Quinn : PRD 48, 2139 (1993)Snyder, Quinn : PRD 48, 2139 (1993)

Interference at equal masses-squared gives information on

strong phases between resonances

02m

02m


Time-dependent Dalitz analysis• Extract and strong phases using interferences between

amplitudes of decay.

003

003

AfAfAfA

AfAfAfA

0 B

0

0

for

for

B

B

3

3

A

A

• Assuming amplitude is dominated by ,and resonances

– The "f"s are functions of the Dalitz-plot and describe the kinematics of B→(S→VS).

– The "A"s are the complex amplitudes containing weak and strong phases. They are independent of the Dalitz variables.

script {} refers to {}


Result with B→ • Hint of direct CP-violation

.)(6.)(113 2717 syststat

Mirror solution not shownWeak constraint at C.L.<5%

2.9

• Likelihood scan of using:

PeTA

PeTAi

i

{}

T =tree amp. P =penguinB

B

04.011.021.0

A

06.047.0 14.015.0

A B

B

213 MBB


Combined α measurement

• The best individual measurement comes from .

• Mirror solution are disfavored, thanks to .

• Good agreement with global CKM fit.

• Combined value:

http://ckmfitter.in2p3.fr

)103( 10

9


Summary

• CP violation has entered a phase of precision measurements thanks to the B-factories.

• The angle of the unitarity triangle has been measured with an uncertainty of ~10°.

• Will still improve.

)103( 10

9

http://ckmfitter.in2p3.fr

Measurements of the angle : , (BaBar & Belle results) Georges Vasseur WIN`05, Delphi June 8, 2005.

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Transcript of Measurements of the angle : , (BaBar & Belle results) Georges Vasseur WIN`05, Delphi June 8, 2005.