K. Honscheid, WSU Apr. 15, 2005 K. Honscheid Dept. of Physics Ohio State University New Results...

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.

K. Honscheid, WSU Apr. 15, 2005 K. Honscheid Dept. of Physics Ohio State University New Results...

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Transcript of K. Honscheid, WSU Apr. 15, 2005 K. Honscheid Dept. of Physics Ohio State University New Results...