CP Violation Studies in B Decays

Vivek SharmaUniversity of California San Diego

vsharma@ucsd.edu

Ringberg Phenomenology Workshop on Heavy Flavors : Rottach-Egern, Germany

2003

Special Thanks !

Gautier Hamel de MonchenaultGabriella Sciolla

Shahram RahatlouH. Sagawa

I have drawn heavily from their recent talk(s) at FPCP’02, APS’03, Moriond’03, CKM’03…

The Road Map For Understanding CP Violation in B Decays

( )0,0 ( )0,1

( )η,ρ

Re

Im

α

βγ

uR tR

cR

Reminder : Promising ways to look for New Physics in B Decays

measure sin2β in several decays sensitive to different

short-distance physics

On the road to γA dream for now

(See Fleischer’s talk) (Discussed this yesterday)

UT

measure/constrain the other 2 angles

improve UT side measurements

+e-e

B0 → J/ψ Ks

B0 → π+ π-

B0 → ΦK0

........etc.

B0 → J/ψ Ks

B0 → π+ π-

B0 → ΦK0

........etc.

CP Asymmetry Measurements at Asymmetric B Factory : in Picture

z

∆z∆t βγ c≈< >

Brec

Btag( )4sΥ

βγΥ(4S) = 0.55

z∆-π

0sK

+π

+µ-µ

Coherent BB pair

B0

B0

µ−

Κ−

Distinguish

B0 and B0

« Flavor Tag »

Distinguish

B0 and B0

« Flavor Tag »

CP Asymmetry in B0 Decays : Notation

)sin()cos())(())(())(())(()( 00

00

mtSmtCftBNftBNftBNftBNtA

ff

CPCP

CPCPCP

∆+∆=→+→→−→

=

2

2

1

1f

f

f

Cλ

λ

−=

+2

2 Im

1f

f

f

Sλ

λ

−=

+

ff f

f

Aqλ ηp A

= ⋅

Scenario 1 :Only one amplitude contributes:

ACP(t) = - (Im λ) sin(∆mt)

Im λ=sin2β, sin2α, etc

Scenario 2 :More than one amplitude contributes

both sin and cos terms present- Sf: depends on Imλ

sensitive to UT angles- Cf: depends on |λ|, direct CP

(ηf)

β− i2e~

0B

0B

CPf

mixing

decay

0=t t

CPfA

CPfA

Data Samples For Sin2β Studies: Babar

before tagging and vertexing cutsSamples of B decays to flavor-specific

final states

Samples of B decays to CP-eigenstateswith charmonium

Note: charge conjugate

decays are implied, unless

specified

angular analysis(not shown)mixed CP

energy-substituted mass

energy difference

Nov 1999- June 2002 data82 fb−1 on-peak – 88 million BB pairs

CP = +1

(not shown)

CP = −1

220 lepton-tagged events

Textbook Example of CP Violation in the B System

Select events with a B candidate reconstructed into a CP-eigenstatecontaining a Charmonium meson and a K-short

Require the presence of a fast lepton (e or µ) in the rest of the event

Split the event sample according to the charge of the lepton (call B0-tag the sample with positively-charged leptons, and B0bar-tag the other sample)

Plot the proper time difference ∆tbetween the two decays (deduced from the distance between the two vertices along the boost axis)

Interpret the observed time-dependent asymmetry in terms of CP Violation amplitude sin2β

although ~90 million Y(4S) decays needed !

e.g.

CP Violation in the B system is not a small effect!

CP Fits to the Proper time difference Spectrum (all flavourTags)

CP=+1CP=-1

sin(2β) = 0.741 ± 0.067stat ± 0.034syst

Unbinned maximum likelihood fit to ∆t distribution

sin2φ1 = 0.719 ± 0.074(stat) ± 0.035(syst)sin2φ1 = 0.719 ± 0.074(stat) ± 0.035(syst)

Belle: CP Violation in b → ccs Transition

B0 → fCP

B0 → fCP

BB

BB

N NN N

−+ vs. ∆t

@ 78 fb−1

Measurement of sin2β

This measurement is statistics limitedat least 1 inverse attobarn needed to reach the level

of systematic errors

systematics include possible subtle effects due to QM interference in the decays of the two B mesons

Some (excellent) assumptions are usually made in such analyses

main systematic errors: knowledge of mis-tagging probabilities and time resolution function

Note: 1 inverse attobarn ≈10 times present statistics

the two neutral B mass eigenstates have same lifetimeindirect CP violation in BB mixing can be neglectedCPT is an exact symmetry

direct CP violation in J/ψ KS-like decays is negligibleJ/ψ KS and J/ψ KL measure the same angle β

Experimental Focus now: start testing these assumptions(I will be very brief about this nothing unusual found)

Phys. Rev. Lett. 89 (2002) 201802

Babar

Search for Direct CPV in B J/ψ K-

20.7 fb−1

~1300 candidates Phys. Rev. D-RC 65 (2001)

b

d

d

−W cc

s

0B ψ/J0K

0K0Bb

d−W

s

d

cc

g

u,c,t

ψ/J

Dominant diagram: color-suppressed tree Gluonic penguin diagam

In SM: expect very little direct CP violation

No fundamental wayto distinguish between direct CPV and indirect CPV in mixingfrom the measurement of | λCP |

Study CPV for isopsin-related charged mode

Experimentally

To be updated with more statistics

Could (sin2β)J/ψKs and (sin2β)J/ψKL Differ ?

?d

cc

s 00 K,K ∗

ψ/Jb

d0B

Grossman, Kagan & LigetiPhys. Lett. B538 (2002) 327

b

d

d

−W cc

s

0B ψ/J

u,c,t0K 0Ksds

d

mixing…In the absence of

and…no possible interference between

How good is the relation

new preliminary result

indirect CPV in K0 mixing: negligible

only possible effect: wrong-flavor decays

no suchthing in SM!

From time-dependent rates, measure:

no sizable deviation from 0 (SM expectation)

860856

purity 96%?

“Sin2β” in other modes: Β → φK

Pure penguin decay, therefore potentially a place to look for New Physics

φ helicity

KK mass

beam energy-substitutedmass

~50 events~175 events

Branching fractions and ACP

new results with 89 million BB pairs

Bb

d,u

−Wsss

gφ

Kd,u

b−W

s

ss

g

u,c,t

φ

Kd,u d,u

B

internal penguin

flavor-singlet penguin

would be enhanced in case of large FS rescattering

Time-Dependent CP Asymmetry: B → φKS0

new results (supercede ICHEP2002)

(expect zero) 84 million BB pairs

In SM, expect

Goodness-of-fit: 23%

Correlation: 7%

Sample

Results

Assuming no direct CPV

Fit on control sample (charged decays)

C=0

Time-Dependent CP Asymmetry B → η′KS0

If non-sss contribution negligible,expect

Results

compatible with isospin-symmetry

prelim. results with 89 million BB pairs

to be submitted to PRL

mostly?

Time-Dependent CP Asymmetry B → J/ψ π0

b

d

d

−W cc

d

0B ψ/J0π

0Bb

d−W

d

d

cc

g

u,c,t

ψ/J

0π

penguin: competing weak phase? tree: color- and

Cabibbo-suppressed

If penguin contribution negligible

Sample

Results

prelim. result with 89 million BB pairssubmitted to PRL

bd d

−Wccd −∗)(D

+∗)(D0B

B → D∗+D−

0Bt,c,ub

dd

−W

d

+∗)(D

cc

g−∗)(D

Cabibbo-suppressed tree b → d penguin

If penguins are negligible

Sample

time-integrated asymmetryResults

(Note: non-CP modes)

new result with 89 million BB pairs submitted to PRL

B → D∗+D∗−

Sample(before flavor-tagging)

Vector-Vector decay (L=0,1,2)possible mix of CP = +1 and CP = −1

Transversity analysismostly CP-even

Results

If penguin contribution negligible

define CP-even parameter

Warning : Prospects for Ambulance chasing ahead !

Theorist !

Putting it all together

Summary of “sin2β” Results from BaBar

“reference” sin2β

pure penguin

mostly penguin?

color- & CKM-suppr’d treecompeting penguin

CKM-suppressed treesmall penguin pollution

All alternate BABAR measurements “agree” with the reference sin2β

within two standard deviations, or betterbut… consistently on the low side

“sin2β”C 0.7

41

Average of Measurements of “sin2β” From Belle & BaBar

Golden mode 7% measurement

B → ππ/Kπ & Quest for α

Simultaneous ππ/Kπ analysis

DIRC

bd d

−Wuud −− ρπ ,

0B ++ ρπ ,0B

t,c,ub

dd

−W

dcc

g

++ ρπ ,

−− ρπ ,

penguins cannot be neglected final results with 89 million BB pairs

Phys. Rev. Lett. 89 (2002) 281802

Note: signal-enriched plots after optimized cut on likelihood ratio, with

projection of fitted likelihood superimposed

0

10

20

30

5.2 5.225 5.25 5.275 5.3

mESGeV/c2

Eve

nts

per

2 M

eV/c

2

mESmES

(a)

0

5

10

15

20

-0.1 0 0.1

∆E GeV

Eve

nts

per

10 M

eV

∆E∆E

(b)

0

50

100

150

5.2 5.225 5.25 5.275 5.3

mESGeV/c2

Eve

nts

per

2 M

eV/c

2

mESmES

(c)

0

20

40

60

80

-0.1 0 0.1

∆E GeV

Eve

nts

per

10 M

eV

∆E∆E

(d)

continuum continuum

CP Asymmetry in Β0 π+π−

Significant contribution from both diagrams: – P/T ~ 1/3 from Br(B Kπ)/Br(B ππ)

– Sππ sin2αeff related to angle α through isospin analysis– Cππ direct CP violation

)sin()cos())(())(())(())(()( 00

00

mtSmtCftBNftBNftBNftBNtACPCP

CPCPCP ∆+∆=

→+→→−→

= ππππ

b uu

dW

ubVb d

u

u

W

T = Tree P = Penguin

gtbV

*tdV

eff: α α 51 @ 90% C.L.Grossman Quinn− − <

Babar: Time-Dependent CP Asymmetry: B → π+ π−

BABARNo CP asymmetry seen in B π+π−04.025.030.0

05.034.002.0±±−=

±±=

ππ

ππ

CS

(a)B0 tags

(b)B0 tags

Eve

nts

/ 1 p

s

∆t (ps)

0.5

-0.5

(c)A

ππ /

2 p

s

0

20

0

20

-5 -2.5 0 2.5 5

Nππ=157 ± 20

)sin()cos())(())(())(())(()( 00

00

mtSmtCftBNftBNftBNftBNtACPCP

CPCPCP ∆+∆=

→+→→−→

= ππππ

Belle: B 0 → π+π−Reconstruction

Mass

Energy differencefrom expected value

(0 GeV if signal)

760 B 0 → π+π− candidates in signal region

Number of expected signal is 2324163+−

B→Kπ

B→ππB→ππ+Kπ

Higuchi @ JPS’03

K. Abe et al. [Belle Collaboration], submitted to Phys. Rev. D, arXiv:hep-ex/0301032.

Belle: CP Asymmetry in B 0 → π+π− Decays

0.080.071.23 0.41

0.77 0.27 0.08C

+−=− ±

=− = + ± ±

S

A

When fixed S = 0 and A = 0,the probability to observesuch large CP violation

is less than 0.1%.

0B π π+ −→

0B π π+ −→

@ 78 fb−1

278 152 @ 95% C.L.φ≤ ≤

Belle Asymmetry Fits for C & S : B 0 → π+π−

aaaaa

Belle : Confidence Region

Constraints on φ2 : Βelle

Constraints on φ2 : Βelle (Sagawa, KEK03)

BaBar: B0 ρ±π∓ and B0 ρ±Κ∓

• Related to the angle α • Compared to B ππ:

– Higer BF: B(B ρπ) ~ 4 x B(B ππ)– “Smaller penguins expected”

• … but challenging analysis – Not a CP eigenstate – 4 configurations: B0 ρ±π∓, B0 ρ±π∓

– 3π final state killer combinatorial backgrounds• Analysis strategy

– Pseudo two-body analysis• avoid interference regions of Dalitz plot

– Continuum background suppressed by NN– Simultaneous fit for ρ+π− and ρ+Κ−

α

b uud

W

d d

ρ−,π−

π+,ρ+

B0 ρ±π∓ and B0 ρ±Κ∓

Combined Maximum Likelihood fit measures:

– BF(B0 ρπ)= (22.6±1.8±2.2) 10-6

– BF(B0 ρΚ)= (7.3±1.3±1.3) 10-6

– and 6 other parameters related to CP: ρπρπρπρπρρπ SCSCAA KCPCP ∆∆ ,, ,, ,

Indication for small penguins

N(ρπ) = 428 ± 34 N(ρΚ) = 120 ± 20

BaBar Preliminary

Time-(in)dependent CP Asymmetry : B0 ρ±π∓ (Κ∓)

• Time integrated direct CP:

• Time dependent CP:

• Asymmetry between rates:

08.017.028.0 ±±=KCPAρ

03.008.018.0 ±±−=ρπCPA

04.018.036.0 ±±=ρπC

03.024.019.0 ±±=ρπS

03.00.250.15 ±±=∆ ρπS

04.00.28 0.180.19- ±=∆ +

ρπC

-- B backg.-- all backg.

First step towards a measurement of α in B ρπ decays.

Full Dalitz analysis with more data

BaBar Preliminary

BaBar Preliminary

Prospects for γ & sin2β+γ Μeasurements

Difficult now because either CP asymmetry is very small or largedata sample or theoretical prejudice is required

Β± → D0CP K±

• Theoretically clean (Gronau & Wyler, Dunietz 1991 saga)• Interference between b u (cs) and b c (us)• Small accessible Branching Fractions ~ 10-7

– B0 → D(*) + π−, ρ−, a1• Theoretically clean measurement of 2β+γ• Interference between b u (cd) and b c (ud) • Tiny, tiny CP asymmetries (in progress)

– B0 →D(*)0 K(*)0 : observation of large rate by Belle– B → ππ, Kπ

• Interference between penguin and tree diagrams• Take ratios of Br’s to eliminate dependence on strong phases • Model dependent - relies on assumptions of factorization, SU(3)

– Leave it to theorists to dissect this

2DD

:seigenstate CP are Dwhere00

CP

0CP

D±=±

2γ

D K )0 --A(B

-

=D K )0 +A(B+

D K )0 -A(B-

2 A(B D K )+0 ++

D K )0 +A(B+ 2 A(B D K )+0 - )(2 0 −− → KDBA CP

)(2 0 ++ → KDBA CP

• Isospin analysis

• Measurements:

Progress in B± D0CPK± γ

)%20.035.031.8()()(

0

0

±±=→→

= −−

−−

πDBBFKDBBFR

)%5.06.18.8()()(

)()(00

00

±±=→+→→+→

= ++−−

++−−

ππ CPCP

CPCPCP DBBFDBBF

KDBBFKDBBFR

06.017.006.0)()()()(

00

00

±±=→+→→−→

= ++−−

++−−

KDBBFKDBBFKDBBFKDBBFA

CPCP

CPCPCPBa

Bar

Prel

imin

ary

Summary of CPV Studies

• CP Violation in B Decays established • Sin2β in “golden mode” is a ~7% measurement • Disagreement (>2σ) between Belle & Babar on CPV in B->pi pi• Some tantalizing results (B ΦΚ) !

– All CPV searches are statistics limited • Hope to get 500 fb-1 each by 2006