Mar.7, 2005

Recent results on CP violation fromBelle
H. Aihara
University of Tokyo373fb-1

BelleBaBarKEK SLACPEP-II加速器とBaBar実験

2

SVD2 installed Summer 2003

The outermost (4th) layer was built with this grant.

34Initial goals for B Factories
Exploring CKM picture or alternative origins for CP violation
for quark sector

Apex at( ρ, η )ηVudVub∗
22 iγ
≈−ρ+
ηe∗
VcdVcbΓ(b → u lν )α = φ2γ = φ3(0, 0)

VtdVtb∗22 −i β≈−(1−ρ)+ηe∗
VcdVcbB 0 - B 0 mixing

β = φ1

τ B and Γ( b → c lν )(1, 0) ρ

β = − argVtd ; γ = argVub* ; α = π − γ − β56

7

Status of φ1 (=β)

φ1 = (23.5 ± 1.6)o(Belle+Babar )910Compelling evidence fordirect CP violation in B0 to π+π- decay
andmodel-independent constraints on φ2(α)
based on 275M BBbar pairs

12

Previously……

Belle 152 M BB
with 372±32 B0→π+π− events

BABAR 227M BB
with 467±33 B0→π+π− events

Sππ = −1.00 ± 0.21 ± 0.07
Aππ = +0.58 ± 0.15 ± 0.07

Sππ = −0.30 ± 0.17 ± 0.03
Aππ = +0.09 ± 0.15 ± 0.04

PRL 93, 021601 (2004)

hep-ex/0501071

CPV with 5.2σ,3.2σ evidence for DCPV
3.2σ difference
13Event Selection• B0→π+π− selection

Pion Identification using aerogel and dE/dx

ε (π ) ≅ 90% p( K → π ) ≅ 11%
Kinematical Selection

5.271 < M bc < 5.287GeV / c 2| ∆E |< 0.064GeV
corresponding to ±3σ

CMS∆E = EBCMS − Ebeam
CMS 2
M bc = ( Ebeam) − ( pBCMS ) 2Flavor Tagging

q: flavor charge

q=+1 tagged as a B0,
q=−1 tagged as a B0

r: dilution factor

r=0 no flavor discrimination,0<r≤1

r=1 unambiguous flavor assignment

14

Event Selection (continuum suppression)e + e − → qq , (q = u , d , s, c)

B flight direction

Event shapeqq

BB(Likelihood Ratio)LR15

B0→π+π− signals from 275M BBbar events(a)Total+ π πKπcontinuum
Three-body

200
150
100
50
0-0.2

00.2 0.4∆E (GeV)

Events/(0.02GeV)

250(LR<0.86)(b)r (flavor tag quality)-0.2

LR (Likelihood Ratio)

Events/(0.02GeV)(LR>0.86)
400
350
300
25020015010050000.2 0.4∆E (GeV)

2,820 candidates containing (666 ± 43) π+π−signal events16

LR>0.86
200(a) q = +1

q=+1Total+ π πKπcontinuum

100

Raw Asymmetry
Raw Asymmetry
Raw asymmetry

Events /(1.25ps)
Events/(1.25ps)
Events/(1.25ps)

Unbinned CP fit results1(c)0.0<r≤0.5
0.0<r≤0.5

0.50-0.50200(b) q = -1

q=−1Total+ π πKπcontinuum

100-11(d)0.5<r≤1.00.5<r≤1.00.50-0.50-50-505∆t+5(ps)-1∆t (ps)Aππ = +0.56 ± 0.12 ± 0.06
Sππ = −0.67 ± 0.16 ± 0.06

-5-5005∆t+5(ps)

1st error statistical,
2nd systematic17

Background subtracted fit projection for all events

πNo.+πof−π πYieldevents

0B tagged

B0 tagged∆E-Mbc 2D fits
to individual
time intervals+ -200tagged
as a B0–0tagged as a B

1000+ -π +π − A

π π asymmetry
CP01-1-505∆∆tt (ps)
(ps)

18

A
AππππNew experimental situation
1.5

1Belle 275M
~2.3σ difference between
Belle and BABAR

0.50BABAR 227M

-0.5

-1-1.5-1.5-1-0.5

00.5

11.5
Sππ ππS19

AππSignificance calculation with Feldman-Cousins method
1Large CP Violation,

0.75(A,S)=(0,0)
1-C.L.=5.62x10-8, 5.4σ

0.5
0.25
0(A,S)=(0,−0.62)
1-C.L.=5.13x10-5, 4.0σ-0.25-0.5-0.75-1-1-0.75 -0.5 -0.25

00.250.50.75

both statistical and systematic
errors are taken into account.

1Large Direct CP
violation, confirmationof the previous Belle
results

Sππ
C.L. = Confidence Level

20

Consistency checks with Time-integrated fits

60

LR>0.86 & 0.5<r≤1.00 tagged
q = +1B(a)50Totalππ:+ 107±13π πKπ:Kπ 42±9continuum
cont:38±14030
20100

consistent with time-dependent fit

Events/(0.02GeV)

Events/(0.02GeV)Aππ = +0.52 ± 0.146050(b)= -1B0qtagged
Total
ππ:
+ - 69±11π π
KπKπ: 43±9continuum
cont: 38±1403020
1000.20.4∆E (GeV)

000.2

Direct CP Violation is evident!

0.4 ∆E (GeV)∆E (GeV)21

Interpretation: φ2 constraint using isospin
M. Gronau and D. London, PRL 65, 3381 (1990)

2Sππ = 1 − Aππsin(2φ2 + 2θ )The cleanest
method toextract φ2We use the HFAG summer 2004 values for thebranching ratios of B0→π+π−, π0π0, B+→π+π0 and direct
CP asymmetry of B0→π0π0.
We use the statistical treatment ofJ. Charles et al., hep-ph/0406184

22Β0 −> π0π0 branching ratio and asymmetry
Belle measurement with 275M BB pairs

Br (π 0π 0 ) = (2.3+−00..45+−00..23 ) × 10 −6
ACP (π 0π 0 ) = +0.44 +−00..5352 ± 0.17

hep-ex/0408101
submitted to PRL

BABAR measurement with 227M BB pairs

Br (π 0π 0 ) = (1.17 ± 0.32 ± 0.10) × 10 −6
ACP (π 0π 0 ) = +0.12 ± 0.56 ± 0.06

hep-ex/0412037
submitted to PRLFirst ACP(B0→π0π0) measurements in summer 2004.

23

1−C.L.

Interpretation : φ2 constraint with isospin

using HFAG
summer 2004
J. Charles et al.,hep-ph/0406184

φ2 (degrees)
95.4% confidence interval
0o < φ2 < 19o and 71o < φ2 < 180o24

Summary of new Belle B0 →π+π− CP results• The fit yields

Aππ = +0.56 ± 0.12 ± 0.06
Sππ = −0.67 ± 0.16 ± 0.06

1st error statistical,
2nd systematic• Large direct CP violation with 4.0σ significance isobserved• The results confirm the previous Belle results.
• Isospin analysis gives at 95.4% C.L.
oo71<φ<1800 < φ2 < 19 &2oo25

Outlook
assuming the current measured values

0.8

Current
All improved(x2)All improved(x4)All improved(x8)0.6Current~0.5ab-1

1 - C.L.

1~2ab-1
0.4~8ab-1~32ab-1

0.2
00

20 40 60 80 100 120 140 160 180
φ2 (degrees)

Takes Super-B factories to really pin down the φ2 value.
26

End

Future prospect

Lpeak = 1.4×1034cm-2s-1
Ltot = 350fb-1 (Feb.8, 2005)
world records !

~1010 BB/year !!
& similar numberof τ+τ-Major upgrade ofKEKB & Belle detector(>1yr shutdown)
Crabcavities

Lpeak (cm-2s-1) 1.4x1034
Lint
330 fb-1

5x1034~1 ab-1

5x1035~10 ab-1

_sin2φ1 result : 274M BB Pairs
1/N·dN/d(∆t)+ qξf = +1+ qξf = −1

Raw asymmetry

Poor flavor tag

J/ψ K0 only

preliminary

sin2φ1 = 0.666 ± 0.046
A = 0.023 ± 0.031
Before upgrade (152M BB)

sin2φ1 = 0.696 ± 0.061
A = 0.011 ± 0.043
Good flavor tag

After upgrade (122M BB)

sin2φ1 = 0.629 ± 0.069
A = 0.035 ± 0.044∆t (ps)