Measurement of 2/ using B Decays at Belle and BaBar

Alexander Somov

CKM 06, Nagoya 2006

Introduction (CP violation in B0 + decays) Measurements in B0 + B 0 B0 0 0

2 constraint from an Isospin analysis

CP Violation in BCP Violation in B00 + + decaysdecays

d

W +

b u

d

u

d

B0

+ (+)

- (-)B0

b

d

d

du

u+ (+)

- (-)

W +

u,c,t

)2sin(

0

2

S

A

Tree Penguin

)2sin(1

)sin(~2

effAS

A

)sin()cos()()()()(

00

00

tmStmABNBNBNBN

direct CP violation

determine 2 using isospin analysis

Tree only Tree + Penguin

Direct CPV Mixing induced CPV

B0 + relatively clean signal, large penguin contribution

B0 not a CP eigenstate, time-dependent Dalitz analysis

B0 +

Advantages of + : small penguin contribution due to relatively small [Babar, hep-ex/0607097] relatively large measured branching fraction for b b u u process

637.036.0

000 10)27.016.1()( BBr

Three main decays used for the extraction of 2 ( )

4.4~)ππBr(B)ρρBr(B

0

0

22// measurement

+ is a VV state 3 helicity states (three helicity amplitudes should be considered) +

H0

H+

H odd) CP 1(

even) CP 1(

even) CP 1

| |

2

2

(00

HHA

HHA

HA

longitudinal polarization

Fortunately, longitudinal polarization dominates

Complications:

015.0013.0024.0977.0

Lf

022.0027.0967.0

Lf

030.0941.0 034.0040.0

Lf

BaBar: hep-ex/0607098

PDG

Belle: PRL96, 171801 2006

CP analysis in B + decays

Complications (cont’d):

‘Dirty’ final state + + 0 0 ; () = 150 MeV large backgrounds

I = 1 contribution due to finite width of [A.F.Falk, Z.Ligeti, Y. Nir, H.Quinn PRD69, 011502, 2004]

Contribution from EW penguin

CP analysis in B + decays (cont’d)

Constraint on 2 /

Extract 2 using an Isospin analysis (similar to + analysis) - ‘model independent’ approach

The penguin contribution can also be bound using flavor SU(3) relations [M.Beneke, M.Gronau, J.Rohrer, M.Spranger hep-ph/0604005] [M.Gronau, O.F.Hernandez,D.London,J.L.Rosner, Phys.Rev.D50,4529 ,1994]

)2sin(1 2effAS 22

eff

200~A

2

~ A

0~ A

00A2

A

0A

Measure A and S:

Use isospin relations [M.Gronau and D.London, Phys.Rev.Letter. 65, 1990]

,2

000

AAATwo amplitude triangles:

000

2AAA

Calculate confidence level applying R-fit method (see next talks) [J.Charles et. Al. Eur.Phys.J.C41:1-131, 2005 ]

Isospin analysis in B ()

)(~)(

)(~)(

)(~)(

00

00

00000

00000

0

0

BAA

BAA

BAA

BAA

BAA

BAA

6 unknowns, and 5 observables: Br’s, A, S ( + 2, not yet measured CP asymmetries in 00)

Common features of B measurements

small branching fractions: 10-6 – 10-5

Large background S/B ~ O(1%)

All types of background contribute: continuum, b c and b u continuum is a dominant background. Use Fisher or neural nets (BaBar) to discriminate Multiple B candidates in the same event. Best candidates selection based on best 0 mass and best 2 of the vertex fit. Events with misreconstructed pions, SCF. Use separate PDFs.

Several variables used to separate signal from backgrounds: mbc, E , m, cos , event topology, flavor, t

Analysis strategy

BaBar Determine signal yield, polarization, CP parameters simultaneously using a multidimensional fit. Loose cuts on kinematical variables more signal events in the fit. Use PDFs for ‘all’ variables to discriminate against background - PDF shapes, correlations among variables (sometimes fits exhibit small bias)

Belle Relatively stringent cuts on kinematical variables. Separate fits for event yields, polarization, and CP parameters. - larger statistical errors

Mbc - E - LR fit results

567N

LR fit projection

high quality taghigh quality

tag

Fit results:

Nevt in the fit = 176843

535 Million BB pairs

NEW Belle results (preliminary)

%20f % 35

f

High quality tag

Low quality tag

)()(19.0

)(07.0)(21.016.007.006.0

29.030.0 syststatS

syststatA

535 Million BB pairs

Preliminary t)}msin( S t)mcos( q(A

4τeP ρρρρ

/τ|Δt|long

B

1q

1

Signal true PDF

fit for two parameters A, S

CP fit results

57615N

high-purity events347 Million BB pairs

Updated this summer hep-ex/0607092

6104.1)2.2(23.5Br

0.0150.013L .024 0 0.977f

mES E

cos

m(0)

Simultaneous fit for the yield, polarization, and CP parameters C and S

Previous BaBar:

Previous Belle:(PRL 96,171801, 2006)

3.26.28.38.22

Br

021.0029.0014.0978.0

Lf

030.0941.0 034.0040.0

Lf

(PRL 95,041805, 2005)

540.30 Br(PRL 95,041805, 2005)

B0 + fit results

hep-ex/0607092

)(21.0)(19.0

)(06.0)(15.007.005.007.0 syststatS

syststatC

Signal true PDF

t)}mcos( C

t)msin( S q( 4τ

eP

ρρ

ρρ

/τ|Δt|long

B

1q

1

B0 tags

B0 tags

background

CP Asymmetries

NEW measurements last summer, hep-ex/0607092 232 Million BB pairs

Extract signal yield, polarization and charge asymmetry using an extended unbinned (7-dimensional) ML fit to mES, E, m()+0, cos+0, xN

493900 N

Ntotal = 74293

Simultaneous fit for the yield, polarization, and charge asymmetry

Measurements in B 0 decays

Determine signal yield from a fit to E distribution Obtain polarization from a simultaneous fit to background subtracted cos + cos 0 distributions Determine charge asymmetry from separate fits to E distributions of B+ +0 and B 0 candidates

Background subtracted m(+) and m(0)

Belle results (old), PRL 91, 221801 (2003)

Background subtracted cos + cos 0

2.137.580 N

Measurements in B 0 decays (cont’d)

85 Million BB pairs

0.030.220.000.100.130.12A0.0210.1060.9480.0420.905 f

7.131.7 2.32.216.8)(10Br

CP

0.0230.027L

3.86.7

-6

0.130.080.912

3.018.20.0440.045

67.54.5 10)8.55.22(

Br

HFAG

Previous BaBar measurement: 04.097.0 03.007.0

Lf

03.023.019.0 CPA

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

B 0 results85 Million BB pairs232 Million BB pairs

Use an unbinned extended ML fit to extract signal yield and polarization 8 dimensional fit: mES, E, m()1,2, cos 1,2, event topology, flavor tags total number of events in the fit 65180, N(00) =

Main components in the fit signal, = 24.2% continuum background (use neural network and tagging information) float parameter values b c background b u background - similar topology: B0 a1 (dominant peaking background), 0f 0, f0f0

- other modes: 0K*0, +0, , +, remaining float normalization

348 Million BB pairs hep-ex/0607097

Evidence for B 00

323198

Evidence for B 00 (cont’d)

637.036.0

000 10))(27.016.1()( systBBr

)(2298 323100 systN

)(05.086.0 11.013.0 systfL

mES E

hep-ex/0607097

background00

Results statistically consistent with previous BaBar measurements, PRL 94, 131801 (2005) Br < 1.1 10-6 at 90% CL

Sourses of dominant systematic errors: PDF shapes, interference with B0 a1 , fit bias

B 00 - last minute results!

6000 10))(19.0)(33.007.1()( syststatBBr )(04.0)(1387.0 syststatfL

mESE

hep-ex/0612021 (12/11/2006)submitted to PRL

background

00

m cos

384 Million BB pairs

)(173210000 systN

Constraint on Constraint on 22//

N.A.)ρA(ρ0.86

100.46)(1.16 )ρ(ρf)ρB(ρ

0.0230.96810)(23.1

)ρ(ρf)ρB(ρ

0.912 103.0)(18.2

)ρ(ρf)ρB(ρ

00

0.120.14

6

00L

00

63.23.3

L

0.0440.045

6

0L

0

Caveats ignore interference with , +00, a1

ignore possible I = 1 contribution neglect EW penguin (all believed to be small)

Branching fractions and polarization fractions used in the calculations(HFAG, Aug. 2006)

(26 ± 6) 10-6

(25 ± 4) 10-6

>1.1 10-6

The isospin triangle is ‘closed’ with new measurements of Br(+), Br(+0), Br(00),

OLD

is not measured. We have6 unknowns and 5 measurements. leads to plateau on 1-CL plot the plateau width depends on Br(00)

Constraint on Constraint on 2 2 // (cont’d)(cont’d)

113/71 2

at 68% CL

1-C

L

B (WA)

B (BABAR)

B (Belle) & B00 (BABAR)

(92 21)

Squashed Isospin triangles at Belledue to large Br(B 0) = 31.7 no ‘plateau’, 2-fold ambiguity

Generally, Isospin analysis allows toextract 2 / with 8-fold ambiguity

)(S A 0000 ρρρρ

If Br(0 0) 0, Isospin triangles squashes

00

Several new results during this year:Several new results during this year: Measurement of CP asymmetries in B + at Belle

Measurement of branching fractions, polarization fractions, and CP asymmetries in B + and B +0 decays at BaBar

First evidence for B 00 decays at BaBar

From an Isospin analysis From an Isospin analysis 22// is constrained asis constrained as

SummarySummary

at 68% CL

New measurements are awaited to improve our knowledge on New measurements are awaited to improve our knowledge on 22//

(Belle first results on Br(B 00) will appear soon)

113/71 2

Backup slides

B0 00

B0 +

B 0

Summary of systematic errors

BB pairs 106 Value BB pairs 106 Value

Br 347 4.1 274 +2.3-2.6

fL 347 +0.015-0.013 274 0.03

A(C) 347 0.06 535 0.07

S 347 +0.05-0.07 535 +0.07- 0.06

BB pairs 106 Value BB pairs 106 Value

Br 232 0.23 85 +3.8-6.7

fL 232 +0.023-0.027 85 0.021

ACP 232 0.10 85 0.03

BB pairs 106 Value

Br 348 0.27

Mixing induced CP violation (sin 2Mixing induced CP violation (sin 222//))

B0 B0

Mixing

b

d

d

b

t

t

*tdVtbV

WW

d

W +

b u

d

u

d

B0

+ (+)

- (-)

Tree

*ubV

udV

*cbcdVV

*ubudVV

1()3()

2() *tbtdVV

*

*

2 argubud

tbtd

VVVV ACP = S sin(mt)

S = sin 22B0

B0

fCP

A

A

pq