Download - K. Honscheid, WSU Apr. 15, 2005 K. Honscheid Dept. of Physics Ohio State University New Results from the BaBar Experiment Part 1: Matter-Antimatter.

K. Honscheid, WSU Apr. 15, 2005

K. HonscheidDept. of Physics

Ohio State University

New Results from the BaBar Experiment

Part 1: Matter-Antimatter Asymmetry

Part 2: CP Violation and the SM

Part 3: Beyond the Standard Model


• Einstein showed us that matter and energy are equivalent

• When matter and antimatter meet, they annihilate into energy

• Energy can also materialize as particle-antiparticle pair

Matter, Energy and the Big Bang

Predict: nMatter/nPhoton~ 0

Exp: nb/n~ (6.1 +/- 0.3) x 10-10 (WMAP)


So how can this happen?

1. Baryon number violation(Proton Decay)

2. Thermal non-equilibrium

3. C and CP violation(Asymmetry between particle and anti-particle)

In 1967, A. Sakharov showed that the generation of the net baryon number in the universe requires:

Transition to broken electroweak symmetry provides these

conditions


• Get equal amounts ofmatter and anti-matter

• Wait…

• See what’s left(in anything)

Experimental Possibilities:


PEP-II Asymmetric B Factory

Stanford Linear Accelerator Center,Stanford, California


The BaBar Experiment


The Upsilon(4S) - a copious, clean source of B meson pairs1 of every 4 hadronic events is a BB pairNo other particles produced in Y(4S) decayEqual amounts of matter and anti-matter

Preparing the Matter – Antimatter Sample

28.0hadr

bb

Collect a few 108 B0 B0 pairs

B mesons contain a b quark and a light anti-quark.mB = 5.28 GeV (~5x mProton)

BB

Thre

shold


Threshold kinematics: we know the initial energy of the system

Analysis techniques

2*2*BbeamES pEm **

beamB EEE

Background Background

(spherical)

(jet-structure)

Event topology

Signal Signal


227 x 106 B0 Mesons

Count B0K+ Decays

227 x 106 B0 Mesons

Count B0K-+ Decays

Is N(B0K+ ) equal to N(B0K-+ )?

Searching for the Asymmetry


How to Tell a Pion from a Kaon

Angle of Cherenkov light is related to particle velocity– Transmitted by internal

reflection– Detected by~10,000

PMTs

c

Particle

Quartz bar

Cherenkov light

Active Detector Surface


BABARB0K+

B0K+

BABARbackgroun

d subtracted

227 x 106 B0 Mesons

Count B0K+ Decays

227 x 106 B0 Mesons

Count B0K-+ Decays

Is N(B0K+ ) equal to N(B0K-+ )?

Searching for the Asymmetry


Using

We obtain

First confirmed observation of direct CP violation in B decays

Direct CP Violation in B Decays

CP

Br B f Br B fA

Br B f Br B f

0

0

9

696

10

n B K

n B K


CP( ) =

Part 2: CP Violation in the Standard Model

CP Operator:

q

q’

J

g

q

q’

J

g*

Mirror

coupling

To incorporate CP violation

g ≠ g*

(coupling has to be complex)


The Kobayashi-Maskawa Matrix

• The weak interaction can change the favor of quarks and lepton• Quarks couple across generation boundaries

• Mass eigenstates are not the weak eigenstates

• The CKM Matrix rotates the quarks from one basis to the other

Vcb Vub

d’Vu

d

Vus

Vu

b

d

s’ = Vcd Vcs Vcb s

b’ Vtd Vtd Vtb b

u

d

t

c

bs

3 2

2

3

=cos(c)=0.22


The Unitarity TriangleVisualizing CKM information from Bd decays

• The CKM matrix Vij is unitary with 4 independent fundamental parameters

• Unitarity constraint from 1st and 3rd

columns: i V*i3Vi1=0

• Testing the Standard Model– Measure angles, sides in as many ways possible– SM predicts all angles are large

β

-i

-i

γ1 1

1 1 1

1 1

e

e

CKM phases (in Wolfenstein convention)

u

d

t

c

bs

Vud Vus Vub

Vcd Vcs Vcb

Vtd Vts Vtb


Understanding CP Violation in B K

A1 = a1 e i1

B0 -+

B0 +-

A1 = a1 ei1 ei1

• include the strong phase (doesn’t change sign)• more than one amplitude with different weak phase; (A = A1+A2)

A1 = a1 e -i1A1 = a1 e-i1 ei1

Asymmetry = = ~ 2 sin() sin(2)= 0

A2 = a2 ei2 ei2

A2 = a2 e-i2 ei2

+

+

|A|2 – |A|2

|A|2 + |A|2

(B) – (B)(B) + (B)

s

u

dd0B

KubV

*usV

b u

Tree decay

ubusVVA *

s

u

dd

0BKg

b

utcu ,,

Penguin decay

tbtsVVA *


B0 B0 Mixing and CP Violation

A neutral B Meson

Mixing frequency md 0.5 ps-1

N(B

0)-

N(B

0)

N(B

0)+

N(B

0)

0B

fiCPA e

CPf

0B

12

2 Mi

M

ie

fiCPA e

CPV through interference between mixing and decay amplitudes

Interference between ‘B B fCP’ and ‘B fCP’

The SM allows B0 B0 oscillations

B0 fraction ~ sin(md t)


Time-Dependent CP Asymmetries

W+c

s

b c

d d

B0

0 0SK K

CP Eigenstate: CP = -1

0 0

0 0

( ( ) ) ( ( ) )( ) Im sin

( ( ) ) ( ( ) )CP CP CP

phys CP phys CPf f f d

phys CP phys CP

B t f B t fA t m t

B t f B t f

Quark subprocess

B0 mixing

K0 mixing

* * **

* * *I m I m I mcscs tbcb td cd tdb ccs

cs cscb tb td cd td

V V V V VV VV V V V V V V

Amplitude of CP asymmetry

sin2

/J

0 0

0 0

( ( ) ) ( ( ) )( ) Im sin

( ( ) ) ( ( ) )CP CP CP

phys CP phys CPf f f d

phys CP phys CP

B t f B t fA t m t

B t f B t f

sin2


t =0

Time-dependent analysis requires B0 flavor tagging

We need to know the flavour of the B at a reference t=0.

B 0

(4S)

The two mesons oscillate coherently : at any given

time, if one is a B0 the other is necessarily a B0

In this example, the tag-side meson decays first.

It decays semi-leptonically and the charge of the

lepton gives the flavour of the tag-side meson :

l = B 0 l = B 0. Kaon tags also used.

tagB 0l (e-, -) =0.56

z = t c rec

sK

t picoseconds later, the B 0 (or perhaps its now a B 0) decays.

B 0

ll

d0B b

W

At t=0 we know this

meson is B0


Step by Step Approach to CP Violation

1. Start with a few x 108 B0 B0

pairs (more is better)2. Reconstruct one B0 in a CP

eigenstate decay mode3. Tag the other B to make

the matter/antimatter distinction

4. Determine the time between the two B0 decays, t

5. Plot t distribution separately for B and B tagged events

6. Extract ACP and sin2

t (ps)

sin 2

sinmt

AC

P(

t)

B tagged

B tagged

t (ps)


Results: sin 2and the observation of CP

CP = -1•B J/ Ks

0, Ks0 +-, 00

•B (2S) Ks0

•B c1 Ks0

•B J/ K*0, K*0 Ks0

•B c Ks0

CP = +1•B J/ KL

0

J/Ks and otherb cc s final states

BaBar result: sin2 = 0.722 0.040 0.023

(12w) sin(2)

w = mis-tag fraction

7730 events

227 million BB pairs


(0,0) (0,1)

(,)

Vub Vud

Vcd Vcb

*

*

Vtd Vtb

Vcd Vcb

*

*

The Unitarity Triangle

[23.3 ± 1.5]o


Ks is not the only CP Eigenstate

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 *

222 iii eeeA

A

p

q

ACP(t)=sin(2)sin(mdt).

sin2


Time-dependent ACP of B→

Blue : Fit projectionRed : qq background + B0→K cross-feed

0B

0B

03.017.030.0")2sin(" 60 10)2.06.07.4()( BB

)M227(33467)( BBBN

BR result in fact obtained from 97MBB


Houston, we have a problem

KK

K

B0 +-

B0 K+-

B0+ 157 19 (4.7 0.6 0.2) x 10-6

B0K+ 589 30 (17.90.9 0.7) x 10-6

Penguin/Tree ~ 30%

q

q


The route to sinPenguin Pollution

• 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 *

)cos()sin()( tmCtmStA dd

sin

)2sin(1 2

C

CS eff

ii

iii

CP eePT

eePTe

2

du

dd

0B

gb

utcu ,,

Penguin decay

tbtdVVA *

Inc. penguin contribution

0

)2sin(

C

S

222 iiiCP eee

A

A

p

q

How can we obtain α from αeff ?

Time-dep. asymmetry :

NB : T = "tree" amplitude P = "penguin" amplitude


How to estimate |eff| : Isospin analysis

• Use SU(2) to relate decay rates of different hh final states (h {})

• Need to measure several related B.F.s

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

)( 0 BAΑ

)( 00000 BAΑ

)( 00 BAΑ

Difficult to reconstruct.Limiting factor in analysis

2| eff

|

)(~ 0 BAΑ

)(~ 00000 BAΑ


Now we need B→

• 61±17 events in signal peak (227MBB)– Signal significance = 5.0– Detection efficiency 25%

• Time-integrated result gives :

6000 10)10.032.017.1()( BB

06.056.012.000 C

B±→±0

• 3 B.F.s– B0– B

– B0

• 2 asymmetries– C

– C

Using isospin

relations and

• Large penguin pollution ( P/T )– Isospin analysis not currently viable in the B→ system

|eff |< 35°


B → Sometimes you have to be lucky

P → VV decaythree possible ang mom states:S wave (L=0, CP even)

P wave (L=1, CP odd)

D wave (L=2, CP even)

We are lucky:

helicity angle

~100% longitudinally polarized!Transverse component taken as zero in analysis

PRL 93 (2004) 231801

22

12

41

22

12

21

2

sinsin)1(coscoscoscos

LL ff

dd

Nd


very clean tags

Time dependent analysis of B→• Maximum likelihood fit in 8-D variable space

32133 events in fit sample

04.003.003.099.0

long

Lf60 10)5430()( BB

)M122( BB

52617)( BN

60 107.4)(.. BBfc

)( tACP

0B

0B

)M97( BB

08.014.0)(

24.033.0 long

S

09.018.003.0)(

longC


• Similar analysis used to search for – Dominant systematic stems from the potential interference from B→a1

±± (~22%)

Searching for B→

1233)( 2220

000 BN

C.L.%90101.1

10)19.054.0()(6

636.032.0

000

BB

)M227( BB

%27Eff.Rec.

c.f. B→B.F.= 4.7 x 106

and B→B.F.= 1.2 x 106

B (B→= 33 x 106


• The small rate of means

– |eff | is small[er]

– P/T is small in the B→ system

(…Relative to B→ system)

– No isospin violation (~1%)– No EW Penguins (~2%)

Isospin analysis using B→000 B

|eff |< 11°

)(11.)(4.)(8100 penguinsyststat

00A

2A

0 0A A

2A

00A2 peng


(0,0) (0,1)

(,)

Vub Vud

Vcd Vcb

*

*

Vtd Vtb

Vcd Vcb

*

*

[23.3 ± 1.5]o


[103 ± 11]o


The 3rd Angle:

Color suppressed

*cb usA V V

*ub csA V V

cbV

*usV

ubV

*csV

3

3 2 2 ie

Basic Idea

0 0

0 0 Use interf erence between and

decays where the ( ) decay to a common fi nal state B D K B D K

D D f

(*)0(*)

(*)0

Size of CP asymmetry depends on | ( )|

~0.1 0.3| ( )|B

A B D Kr

A B D K


First Look at the Data

75 1318 7

K K

0 76 13SK CP CP

214 pairs M 214 pairs M

BABAR-CONF-04/039Only a loose bound on rB with current statistics: (rB)2 = 0.19±0.23

Several other methods are being investigated

More data would help a lot…


Combined Experimental Constraint on

o

indirect constraint

8fi t: 58 7

CKM

o

From combined

GLW and ADS fi t:

2051 34

BABAR & BABAR & Belle Belle

combinedcombined

BABAR & BABAR & Belle Belle

combinedcombined


(0,0)

Vub Vud

Vcd Vcb

*

*

Vtd Vtb

Vcd Vcb

*

*


[23.3 ± 1.5]o

[103 ± 11]o

[51+20-34]o


Putting it all together

• The complex phase in the CKM matrix correctly describes CPV in the B meson system.

• Based on SM CPV the baryon to photon ratio in the universe should be nb/n~ 10-20

• Experimentally we find nb/n~ (6.1±0.3) x 10-

10 (WMAP)


• FCNC transitions bs and bd are sensitive probes of new physics

• Precise Standard Model predictions.

• Experimental challenges for bd (B B)– Continuum background– Background from bs (BK*) (50-100x bigger)

Part 3: Consistency Checks

Ali et al hep-ph/0405075

Part 3: Beyond the Standard Model

0,1

2

3( ) 0,0

1( )

tb

cd cb

V

V V

tdV


Combined B00,B0,B-- results

• No signals observed

@90% CL


CKM constraints from B()

BABAR BF ratio upper limit < 0.029 → |Vtd/Vts| < 0.19 (90% CL)

Penguins are starting to provide meaningful CKM constraint

(2,R) = (0.85,0.10) Ali et al. hep-ph/0405075

no theory error

with theory error (2,R) = (0.75,0.00)

95% CL BABAR allowed region

(inside the blue arc)


New CP Violating Phases in Penguin Decays?

b

dd

W cbV

csV

c /J

s0K

c

+ mixing CP = -e-2

+ mixing CP = -e-2

+ mixing CP = -e-2

b st

ss

d

W

d 0 K

, ,...

b st

dd

d

W

d

0 K

0 , ,...

Vtb

Vts*

Vtb

Vts*


Update on BKo

0Bb s

s

sd

d

W

g

, ,u c t

0SK

0

0

0.070 50 0.25 0.040 00 0.23 0 05

CP K

K

S .

C . .

0 0LB K

98 ± 18 events

0 0SB K

hep-ex/0502019

prel

imin

ary

114 ± 12 events

SM

Belle[BELLE-CONF-0435]


Reaching for more statistics – B 0 K 0 revisited

• Analysis does not require that ss decays through resonance, it works with non-resonant K+K- as well– 85% of KK is non-resonant – can select clean and high statistics

sample– But not ‘golden’ due to possible additional SM contribution with ss

popping

• But need to understand CP eigenvalue of K+K-KS: has well defined CP eigenvalue of +1, - CP of non-resonant KK depends angular momentum L of KK pair

• Perform partial wave analysis– Estimate fraction of S wave (CP even) and P wave (CP odd) and

calculate average CP eigenvalue from fitted composition

0K

b

dg

t

d

ss

s

W

0BK+K- Nsig = 452 ± 28

(excl. res.)

b

d

0BK

g

t

s

us

u

W 2~tb tsV V

0Kds

K b

d

0BK

s

us

u

W

0Kd

s

K

4~ iub us uV V R e

OK Not OK


CP analysis of B K+K- KS

• Result of angular analysis

– Result consistent with cross checkusing iso-spin analysis (Belle)

• Result of time dependent CP fit

2

-even 2 20.89 0.08 0.06s

CPs p

Af

A A

0 0

-even 0 0

2 ( )0.75 0.11

( )S S

CP

B K K Kf

B K K K

0

0

0.42 0.17 0.04

0.10 0.14 0.06S

S

K K K

K K K

S

C

fSK+K-KS/(2fCP-even-1)] =

+0.55 ±0.22 ± 0.04 ±0.11(stat) (syst) (fCP-even)


More penguin exercises – B0 KS KS KS

• Use beam line as constraint and acceptonly KS with sufficient number of SVXhits.

• Decay B0 KS KS KS is ‘golden’ penguin – little SM pollution expected

• Although 3-body decay, only L=even partial waves allowed:– CP(KSKSKS) = CP(KS) = even

• Result consistent with SM

05.034.0

04.071.028.025.0

38.032.0

C

SK0

b

d

0BK

g

t

s

us

u

W 2~tb tsV V

0Kds

K sddssd

K0

K0

K0

hep-ex/0502013

Ger

shon

, Haz

umi

hep-p

h/04

0209

7


IP-Constrained Vertexing

Vertex precision depends on number of hits in SVT

For 4 hits, t resolution as good as with charged-tracks (60% events)

Crosscheck with J/KS:

Constrain decay products to beam-spot in x-y:

beam

0

B0

+

inflated beam

4m

200m

KS

Same technique as Ks0

hep-ex/0503011


Combined “sin2” Results

sin2β

…but comparison ignores subleading diagrams !

sin 2 0.47 0.07penguin

sin2β

sin2βPenguin±

sin2β

+


Corrections: b→s Decay Amplitude ~ VubVus

*

• Decays involving Vub enter with decay phase • Doubly-CKM suppressed w.r.t dominant diagram

iufusub eAVV 4)(*

b u

d

uWs

d

bs

d

u

W

u

d

ss

color-allowed treecolor-suppressed tree

Contribute to ’Ks, f0Ks, Ks, but not Ks[in KKKs (requires ss popup from soft g)]

Contribute to non-resonant KKKs (requires ss popup from soft g)

Contributes to all b sss modes

b

dd

sW

u

sZ,g, s

penguin


• size of possible discrepancies Δsin2β have been evaluated for some modes:

– estimates of deviations based on QCD-motivated specific models; some have difficulties to reconcile with measured B.R.

• Beneke at al, NPB675• Ciuchini at al, hep-ph/0407073• Cheng et al, hep-ph/0502235• Buras et al, NPB697• Charles et al, hep-ph/0406184

– model independent upper limits based on SU(3) flavor symmetry and measured b d,sqq B.R.

• [Grossman et al, PRD58; Grossman et al, PRD68; Gronau, Rosner, PLB564; Gronau et al, PLB579; Gronau et al, PLB596; Chiang et al, PRD70]

Adding Theoretical Uncertainties

2xΔ

sin2

β‘naive’ upper limit based on final state quark content,CKM (λ2) and loop/tree (= 0.2-0.3) suppression factors

[Kirkby,Nir, PLB592; Hoecker, hep-ex/0410069]


Conclusion• Almost 40 years after the discovery of CP violation

in the kaon system we are finally in a position to improve our understanding of CP violation in the Standard Model

• Belle and BaBar give consistent results for sin2. Both work extremely well

• The SM prediction of a single phase in the CKM matrix as cause of CP violation appears to be correct.

• We now know how to distinguish between matter and anti-matter aliens.

• New Physics will be needed to explain the baryon asymmetry in the universe

• Will we find hints in CP phases and/or rare decays?• Stay tuned as more data is coming in.