Cracking the CKM Triangle – B A B AR ’s Next Step – Masahiro Morii Harvard University B A B AR...

Cracking the CKM Triangle

– BABAR’s Next Step –

Masahiro MoriiHarvard UniversityBABAR Collaboration

October 2003

Oct 3, 2003 Masahiro Morii 2

Outline Very brief introduction

CKM triangle and CP violation in the B system BABAR and PEP-II

What we can do today, and in 3 years Measurements

Angle from B KS/L , KS , ’KS

Angle from B

Angle from B D, DK |Vub| from B Xul decays

Summary


CKM Matrix CKM matrix appears in the weak Lagrangian as

Unitary matrix translates mass and weak basis 3 real parameters + 1 complex phase

CPV in the Standard Model is uniquely predictive Attractive place to look for New Physics

. .2

ud us ub

cd cs cb

td ts tb

L

L L L L

L

V V V

V V V

V V V

dg

u c t s W h c

b

L

The only source of CPV in the Minimal SM

2 3

2 2

3

12

12

2

1 ( )

1

(1 ) 12

L

L L L L

L

i

i

dg

u c t s

A

A A

WA

b

L

Wolfenstein

parameters


Why CP Violation? Standard Model is unreasonably successful

It predicts everything we measure, while We all know it’s wrong

BIG failing: Baryogenesis Matter-dominant universe is created through:

CP violation Baryon number violation Non thermal equilibrium

SM prediction falls way short of reality CKM mechanism was a postdiction of CPV

Never tested (before BABAR) its predictive power

All three availablein the Standard Model


Unitarity Triangle V is unitary Consider

Dividing by gives the familiar triangle

Non-zero angles CP violation All sides are O(1) Can test closure with realistic

experimental precision

0ud ub cd cb td tbV V V V V V 3

cd cbV V A

1

*

*

*

*

*

*

arg

arg

arg

td tb

ud ub

cd cb

td tb

ud ub

cd cb

V V

V V

V V

V V

V V

V V

td tb

cd cb

V V

V V

ud ub

cd cb

V V

V V


Anatomy of B0 System B0-B0 system very similar to K0 system

Mixing through box diagrams Coupling constants appear as

Mass eigenstates BH and BL are linear combinations

Lifetime H and L close Ignore Follow the time evolution…

W+

W-

s/b

d

d

s/b* * * 2 5( ) ( ) ( )us ud cs cd ts tdV V V V V V O O O A * * * 3 3 3( ) ( ) ( )ub ud cb cd tb tdV V V V V V O A O A O A

0 0

0 0

L

H

B p B q B

B p B q B

2 2 1p q Mass difference m

causes mixing


B0 Evolution and Decay Starting from pure B0(B0) state, after time t

Now, consider decays into a CP eigenstate fCP

It’s trivial (just tedious) to calculate the decay rates

0 0 0

0 0 0

( ) cos sin2 2

( ) sin cos2 2

B

B

im t t

im t t

mt q mtB t e e B i B

p

p mt mtB t e e i B B

q

0 0f CP f CPA f B A f B H H

20 0

20 0

( ( ) ) ( )

( ( ) ) ( )

CP CP

CP CP

B t f f B t

B t f f B t

H

H

Neat problem for anundergrad. QM exam


CP Asymmetry

2

2 2

1 2Im

1 1

f f ff f f f

ff f

AqC S λ η

p A

0B

0B

CPfm

ixing

fA

fA

Scenario 1:There is only one diagram

For B0 J/KS , -Im(f) = sin2

Scenario 2: More than one diagram contribute both sin and cos terms will survive Sf depends on Im UT angles Cf depends on || direct CP

)sin()cos(

))(())((

))(())(()(

00

00

mtSmtC

ftBNftBN

ftBNftBNtA

ff

CPCP

CPCPCP

f = CP eigenvalue of fCP

1f fA A 0, Im( )f f fC S

( ) Im( )sin( )CP fA t mt


Measuring CP Violation

Experiments must do 3 things: Produce and detect B fCP events

Typical BR: 10-4 – 10-5

Need a lot of lot of lot of lot of B’s Separate B0 from B0 = “Flavor tagging”

Use 4S B0B0 and tag one B

Measure the decay time Measure the flight length ct But B’s are almost at rest in 4S decays

0 0

0 0

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

( ( ) ) ( ( ) )CP CP

CP f fCP CP

N B t f N B t fA t C mt S mt

N B t f N B t f

Solution:AsymmetricB Factory


Three Ingredients

Ingredient #1:Exclusivereconstruction

Ingredient #2:Flavor tagging

Ingredient #3: t determination

e- (4S)

B0

B0

e-

+

-

Breco

Btag

e+

z~ c t

+

-

0 0

0 0

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

( ( ) ) ( ( ) )CP CP

CP f fCP CP

N B t f N B t fA t C mt S mt

N B t f N B t f


Asymmetric B Factory Collides e+e- at ECM = m(Y4S) but with E(e+) ≠ E(e-)

PEP-II: 9 GeV e- vs. 3.1 GeV e+ = 0.56 The boost allows measurement of t

Collides lots of them: Ibeam = 1 – 3A PEP-II luminosity 6.6 x 1033/cm2/s = 6.6 Hz/nb

That’s >2x the design KEKB has hit 1 x 1034/cm2/s

( ) 1nbe e bb


Integrated Luminosity

>100 fb-1/expt. accumulated Physics results used 90-130 fb-1 so far


Luminosity Projection – PEP-II

That’ll give BABAR a billion B mesons to play with

Inte

gra

ted lum

inosi

ty [

fb-1]

Peak

lum

inosi

ty [

10

33]

5

10

15

200

400

600

PEP-II plans to

deliver 500 fb-1

by end 2006


Luminosity Projection – KEKB

KEKB also shoot for 500

fb-1 by end 2006


Detector: BABAR (or Belle)

Precise vertex with a silicon strip

detector

Charged particle momentum with a

drift chamber in a 1.5 T field

Photon energy with a CsI(Tl)

crystal calorimeter

Particle ID with a Cerenkov detector

(DIRC in BABAR,aerogel in Belle)

Muons detected after penetrating

iron yoke


Harvard Group At Work

New 3D track trigger systemfor better backgd. rejectionat higher luminosity

“ZPD”


B0 Charmonium + K0

The “golden mode” Theoretically clean

Only the tree diagram matters Experimentally clean “Large” BF (~10-4)

CP sample in 89 M BB pairs

0Kb

c

sc

d0B

/J

d

ACP(t) = sin2 sinmt

Mode CP Nevents

J/KS , (2S)KS , cKS , cKS -1 1506

J/KL +1 988

J/K*0(KS0) mixed

147

Full CP sample 2641


CP Fit sin2

CP=+1

CP=-1

sin2 = 0.741 ± 0.067stat ± 0.034syst

BABAR 81 fb-1 PRL 89, 201802 (2002)


Unitarity Triangle World average:sin2 = 0.736 ± 0.049

Excellent agreement with SM constraint from indirect (non-CPV) data

Does that mean no New Physics?

Observed CP asymmetry consistent with

CKM mechanism being the dominant source of

CPV

sin2 vs. indirect constraints


Next Step We’ve achieved(sin2

Already more precise than the indirect constraints Use it as the reference!

B0 K0 is a tree decay New Physics may be hiding

in more suppressed diagrams Strategy: Measure “other aspects” of the CKM

triangle Modes with different Feynman diagrams and Clean theoretical interpretations

Look for inconsistencies = New Physics

0Kb

c

sc

d0B

/J

d


Cracking the CKM Triangle Let’s measure everything we can!

ud ub

cd cb

V V

V V

td tb

cd cb

V V

V V

Bs mixing

at Tevatron

Vub from charmless semileptonic B

decays

sin2 from penguin

decays, e.g. B K

sin2 from B decays

from B D and

B DK decays


sin2 Measurements “Redundant” measurements using other decay

modes Different diagrams Different sensitivity to New

Physics Loop diagrams are particularly interesting

Theoretically clean modes are more useful Single-diagram decays preferred

Modes under study

Final states Dominantdiagram

Otherdiagrams

KS Penguin Negligible

’ KS Penguin Tree

D* D*, D* D Tree Penguin

Clean

Less clean


B0 /’ KS

Dominated by b sss penguin ACP

SM = sin2 = ACP(J/ KS) New Physics may enter the loop

KS is pure-penguin As clean as J/KS

Small BR: 7.6 x 10-6

’KS has tree diagrams too Cabbibo- and color-suppressed |A/Ā| ~ 1 within a few % Larger BR: 5.5 x 10-5

’ decays harder to reconstruct

b

d

uu

sd

W

0K

s

d0K

s

s,


Penguin Signals

BABAR KS

BABAR ’KS

Belle

Preliminary LP’03


Penguin CPV Results Preliminary LP’03

Something very strange is happening here…


B0 KS CP Fits Preliminary LP’03

BelleBABAR

B0 tags

B0 tags

ACP

Low-purity tags High-purity tags


B0 ’ KS CP Fits Preliminary LP’03

BelleBABAR

B0 tags

B0 tags

ACP

Low-purity tags

High-purity tags


Status of Penguins B0 KS

Belle 3.3 from J/KS Prob. < 0.1%

BABAR – Belle = 2.1 Prob. = 3.6%

Average = –0.14 ± 0.33 2.6 from J/KS

B0 ’KS

Average = 0.27 ± 0.21 2.2 from J/KS

Do we have a hint of New Physics? Theorists “told you so” for this very decay mode Too early to tell 4x more data will settle the case



from B D and

B DK decays

sin2 from penguin

decays, e.g. B K

from B decays

ud ub

cd cb

V V

V V

td tb

cd cb

V V

V V

|Vub| from charmless semileptonic B

decays


Measuring Angle Tree diagram of B0 +- should give us sin2

But there are penguin diagrams

b cc

s

W

cbVb u

u

d

W

ubV

0SB J K 0B

sin 2 sin 2

b uu

d

W

ubV

effsin 2b d

u

u

W

T = Tree P = Penguin

gtbV

*tdV


Taming Penguins To estimate eff – , we need:

P/T ratio – about 0.3 from (B K)/(B ) = strong phase difference between P and T

Gronau & London (1990) suggested using isospin relations0

0

0 0 0

( ) 2 2

( )

( )

B T P

B T C

B C P

A

A

A

b uu

d

ddb d

u

u

dd

b u

u

d

dd

T

C

P

Measure BF for all modes and combine

Extract eff – from data


Isospin Analysis Isospin analysis requires BF(B0 00) separately

for B0 and B0

Too hard for BABAR/Belle Only average measured Use BF(B0 00) to put upper bound on eff –

Grossman and Quinn, 1998; Charles, 1998

Gronau, London, Sinha, SinhaPLB 514:315-320, 2001

0 0( ) ( )BR BR

eff2( )

Allowed assumed

0( )1.3

( )

BR

BR


Observation of B0 00

BABAR has observed B0 00

at 4.2 significance

Weak limit on eff –

hep-ex/0308012

0 0 0 6( ) (2.1 0.6 0.3) 10BF B 0 0 0

0

( )0.38 0.13

( )

B

B

Allowed

2(

eff –

)


CPV in B0 +-

B-Physics News of 2002:Belle “discovery” of large CPVin B0 +-

PRD 68 (2003) 012001 CPV ≠ 0 at >99.9% CL Not seen by BABAR

2.6 discrepancy Did more data help?

BABAR

Belle


Brief History

BABAR 33×106 BB

BABAR 60×106 BB

BABAR 88×106 BB

Belle 45×106 BB

Belle 85×106 BB

BABAR 123x106 BB

Preliminary LP’03

New world average:

S = -0.58±0.20C = -0.38±0.16


CP Asymmetries

BABAR preliminary Belle PRD 68 (2003) 012001

B0 tags

B0 tags

B0 tags

B0 tags


Status of eff

BABAR-Belle compatibility improved from 2.6 to 2.0 Waiting for new result from Belle

Interpretation of eff remains murky BF(B0 00) too large for useful limit on |eff – | Full isospin analysis beyond reach of existing B

factories Several model-dependent analysis proposed

BABAR (preliminary) Belle (PRD 68, 012001)

Average

S 0.40 ± 0.22 ± 0.03 0.58 ± 0.20

C 0.19 ± 0.19 ± 0.05 0.77 ± 0.27 ± 0.08 0.38 ± 0.16

0.080.071.23 0.41


Status of Different interpretations

with various assumptions“agree” with the indirectconstraint of Theoretical error???

Experimental efforts areshifting towardB0 , final states Interference between

resonances give extra information for |P/T| and Broad on top of non-resonant makes analyses

incredibly complicated

indirect



from B D and

B DK decays

sin2 from penguin

decays, e.g. B K

from B decays

ud ub

cd cb

V V

V V

td tb

cd cb

V V

V V


decays


Why |Vub|

Measurement of sin2 has become more accurate than the indirect constraint Width of the indirect

ellipse is determined by|Vub/Vcb|

Better measurement of |Vub|

More stringent test of the Unitarity

Triangle

Vub


Measuring |Vub|

Measure the rate of charmless semileptonic decays

Catch: charm background

There are many techniques Exclusive:

Better S/B Inclusive: Lepton endpoint spectrum, etc.

Better efficiency

2( ) ubb ul V

b u

l

W

ubV

2

2

( ) 1

( ) 50ub

cb

Vb ul

b cl V

or B l l That’s not a good sign…

Vub


Why |Vub| Is Hard

InclusiveE

xclusive

Poor S/B ratio

S/B bette

r

Error in extrapolation to full acceptance

Model-dependent calculation of FF

PDG 2002, p. 706PDG 2002, p. 706

Vub


How To Improve |Vub|

Measure inclusive (B Xul) Exclusive needs better FF calculation Lattice QCD

Goal: better S/B ratio + larger kinematical acceptance Minimize charm background Reduce extrapolation

Three kinematical variables in the Xul final state

We need a large sample of clean, isolated, and unbiasedB decays “B beam”

El lepton energy easy to measure

q2 (l- mass)2 needs momentum

mXhadron system mass

needs all hadrons

Want to use all of them for optimal efficiency and S/B

Vub


Tagged-B Events We have a large sample of (4S) BB events

with one B fully reconstructed ~1000 decay channels Efficiency ~0.2%/B

Look at the other B inthese events (“recoil” B) Almost-pure B0, B± with

known momentum Purity known from mES fit Subtract background using sideband

0 ( )

( )0

B D Y

B D Y

Y± is any combinationof ±, K±, KS and 0

Ideal sample for branching fraction measurements

Vub


BF(B Xul)

Start from the recoil-B sample Find a lepton with p > 1 GeV Calculate mass of the remaining system “X”

Know pB, missing () mass = 0

2-C fit improves (mX) from 500 350 MeV

Normalization from fitting tag-B mass

All events with a leptonMostly B Xcl mX > 1.55 GeV

Xul enrichedto ~60%

Vub


BF(B Xul) |Vub|

Fit the mX distribution to extract BR

Use OPE calculation

1

( )

( )

0.0206 0.0025( )

0.0023( ) 0.0036( , )

uB X l

B Xl

stat

syst

hep-ex/0307062submitted to PRL

1 2

31

( ) 1.55ps0.00445 (1 0.020 0.052)

0.002

4.62 0.28( ) 0.27( ) 0.40( , ) 0.26 10

ubb

b ulV

stat syst

B

mbOPE

Vub


Theoretical Errors Signal efficiency depends on (El, q2, mX) distribution

Differential rate predicted at parton level to O(s) Depends on the b quark mass and its Fermi motion

Leading systematics for |Vub| Parameterized in

Same parameters determine (El, q2, mX) for B Xcl Above values come from CLEO’s electron spectrum We should be able to improve!

Measure both El and mX spectra in B Xcl mX requires the recoil-B technique

210.480 0.120GeV, 0.300 0.105GeV

Vub


Hadron Mass Moment Start from recoil-B with lepton

Calculate mX as in the |Vub| analysis

Subtract (small) B Xul contribution

Calculate moments <mX> <mX2> <mX

3> <mX4>

Vary the lepton p cut from 0.9 to 1.6 GeV

Vub

BABAR preliminary

Coming Soon: Combine with Ee spectrum and fit determine and 1


Status of |Vub|

BABAR/Belle/CLEO are working hard on |Vub| BABAR is leading with

the recoil-B technique Improvements

continue El and mX spectra

Better and 1 Cut on q2 Reduced

theoretical error Tag B with

semileptonic decays higher efficiency

Vub



from B D and

B DK decays

sin2 from penguin

decays, e.g. B K

from B decays

ud ub

cd cb

V V

V V

td tb

cd cb

V V

V V


decays


Measuring Angle No magic bullet for Many difficult ideas

Most use interference between two competing diagrams to measure sin(2 + )

Modes under study include: first results from BABAR, Belle first result from Belle no results yet And a whole lot more…

0 (*)B D

0B D K 0B D K


B0 D(*) Analysis Cabbibo-favored and suppressed amplitudes

Amplitude ratio r ~ 0.02 Weak phase from Vub

Strong phase unknown

*cb udA V V

2*

212

* 1i i i i iub cd

cb ud

V VAe e e e e

A V Vr

Time-dependent CPV with

ACP = r sin(2 + )

*ub cdA V V


CPV in B0 D(*)

Measuring 4 ratesshould give useverything, but…

r is small (~0.02) cannot be extracted from C We need r from elsewhere to determine sin(2 + )

0 (*)

0 (*)

0 (*)

0 (*)

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

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

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

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

t L

t L

t L

t L

B t D e C mt S mt

B t D e C mt S mt

B t D e C mt S mt

B t D e C mt S mt

2

(*)

2(*)

11

1

rC

r

(*)

(*)2(*)

2sin(2 )

1

rS

r


Estimating r Theoretical models

Estimates are around r = 0.02 with ~20% spread Measure B+ D+0

Isospin symmetry: O(10-7) We can’t measure this for a while

Use B0 Ds+- assuming SU(3)

0 (*) (*) 0( ) 2 ( )A B D A B D

* 0.0050.007( ) 0.019 0.004, ( ) 0.017r D r D

plus ±30% theoretical error


B0 D(*) Signal BABAR 88x106 BB

Fully reconstructed signal

B0 D(*)-+ B0 D(*)+-

B0 D(*)-+ B0 D(*)+-

0 (*)

0 (*)

0 (*)

0 (*)

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

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

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

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

t L

t L

t L

t L

B t D e C mt S mt

B t D e C mt S mt

B t D e C mt S mt

B t D e C mt S mt

Submitted to PRL


B0 D(*) Results

Measurements with ~100% statistical errors are arriving Small CPV CPV of the tag side dominates

systematics

2r sin(2+)cos 2r sin(2+)sinBABAR (82/fb)fully-reconstructedhep-ex/0309017

D–

0.038±0.038±0.021

0.025±0.068±0.035

D*–

0.068±0.038±0.021

0.031±0.070±0.035

BABAR (82/fb)partially-reconstructedhep-ex/0307036

D*–

0.063±0.024±0.017

–0.004±0.037±0.020

Belle (140/fb)fully-reconstructedhep-ex/0308048

D 0.058±0.038±0.013

0.036±0.038±0.038

D* 0.063±0.041±0.021

0.030±0.041±0.034

Pre

limin

ary


B± D0K± Analysis

Phase between the two diagrams = Interference if D0/D0 decay into a common final

state,e.g., KS, KSKK

CPV:

B+u

cu

b

su

D0

K+

B+

usu

b uc D0

K+

*cb usA V V *

ub csA V V

( )0( ( ) ) 1 B DiiS B DA B D K K r r e e

|Vub/Vcb|D0 KS ratio

strongphase

s


B± D0K± Analysis Strong phase D in the D0 decay comes from FSI

Varies across the Dalitz plot Select a region where

single resonance dominates, or

Fit D as a function over theDalitz plane

Things get tricky

Belle hep-ex/0308043preliminary


B± D0K± SignalBelle 140/fb (hep-ex/0308043) preliminary

B- vs. B+


B± D0K± Result Belle result: = (95±23±13±10)°

Last error due to D0 decay model, i.e., how to fit the Dalitz plot

Encouraging first step BABAR analysis in

progress Summer ’04?

Stat. only

Stat. + syst.90% CL

Belle 140/fb(hep-ex/0308043) preliminary


Status of Serious efforts started to measure in several

channels First results from B0 D and B± D0K± show

promise B0 D – Cleaner analysis. How we get r? B± D0K± – Dalitz analysis powerful but messy

No “golden mode” Many measurements must be combined – How?

Remember: we are trying to discover non-SM effect Careless averaging may wipe out New Physics Area of intense debate



from B D and

B DK decays

sin2 from penguin

decays, e.g. B K

from B decays

ud ub

cd cb

V V

V V

td tb

cd cb

V V

V V


decays


Summary (1) BABAR/Belle working hard to crack the Unitarity Triangle

The Standard Model is holding remarkably well Tantalizing shifts observed in sin2 from penguin

decays Too early to declare death of the SM 4x data in 3 years will tell

from B seems harder than we hoped Dalitz analysis of B , pursued

New and improved |Vub| measurements with recoil-B Coming soon: better and 1 to reduce theory error

Early measurements of started to appear Huge effort going into the last angle


Summary (2) With 109

B’s/experiment by 2006, we will learna lot more about the Unitarity Triangle Is it really closed, or

will we see a sign of

New Physics?

Cracking the CKM Triangle – B A B AR ’s Next Step – Masahiro Morii Harvard University B A B AR...

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Transcript of Cracking the CKM Triangle – B A B AR ’s Next Step – Masahiro Morii Harvard University B A B AR...