Recent Results from B A B AR

Recent Results from BABARP.-Fabrizio Salvatore

Royal Holloway College, University of LondonFor the BBAABBARAR Collaboration

Hadron Structure 2002, Herl’any

22-27 September 2002

Measurement of sin2Measurement of sin2eff

Future: and sin (2+

September 26, 2002 Fabrizio Salvatore, Royal Holloway College 2

The search for CP violation with asymmetric e+e- collider

PEPII and the BaBar Experiment sin2 measurement:

The golden modes: b -> ccs The Cabibbo-suppressed modes: b -> ccd The pure penguin modes: b -> sss

sin2eff measurement: CP asymmetries in +- and K+-

+0 and 00 decay rates CP asymmetries in +- and +K-

Future:and sin(2 +) Asymmetry in B ->D0

(CP)K decay B0 ->D* (n) decays

Conclusions

Outline

--


Physics principles: CP violation in the SM

The only source of CP violation in the SM is the KM phase that appears in the CKM matrix

CP from complex component of Vub and

Vtd

Unitarity Triangle comes from the unitarity of the

matrix

1

2

3

, and constrained by CP asymmetries in B decays


Time-dependent CP violation from B0-B0 mixing

B0

B 0

fCP

BL ,H p B0 q B0 b

d

d

bu,c,t

u,c,t

top quark box introduces: Vtb Vtd*

f(t )e t /

41S f sin(mdt)C f cos(mdt)

md = mH - mL

W W

Cf 1 f

2

1 f2

Sf 2 Im f

1 f2

f qp

A(B0 fCP)

A(B0 fCP)

qp

~Vtd

Vtd*

f (B0 fCP)

f (B0 fCP)

Direct CP violation if multiple amplitudes with different phases

Purely CP violation in interference of decays with and without mixing


PEPII performancesPeak luminosity: 4.60 x 1033cm-2s-1

(exceeded design goal 3.0 x 1033)

PEP-II delivered 99 fb-1

BaBar recorded 94 fb-1

For sin2 and sin2 used:On peak 81 fb-1

88M BB pairsOff peak 10 fb-1

Peak luminosity: 4.60 x 1033cm-2s-1 (exceeded design goal 3.0 x 1033)

PEP-II delivered 99 fb-1

BaBar recorded 94 fb-1

For sin2 and sin2 used:On peak 81 fb-1

88M BB pairsOff peak 10 fb-1


BABAR Detector

SVT: 5 double side layers. 97% efficiency, 15 m z hit resolution (inner layers, perp. tracks)Momentum resolution (SVT+DCH): (pT)/pT = 0.13 % pT + 0.45 %

DIRC: 144 quartz bars. Provide K- separation 4.2 @ 3.0 GeV/c 2.5 @ 4.0 GeV/c EMC: 6580 CsI(Tl) crystals. Energy resolution: E/E = 2.3 %E-1/4 1.9 %


B0-B0 events at the (4S) resonance

Boost: = 0.55

Start the ClockCoherent BB pair

B0

B0

z

t z c

K-

Flavour tag and vertex reconstructi

on

Flavour tag and vertex reconstructi

on

Exclusive B meson and vertex reconstruction

Exclusive B meson and vertex reconstruction

KS

Z

Compute f+ (t)

+e-e

4S Btag

Brec


Vertexing and tagging algorithms

Brec vertex from charged Brec daughters

BTag vertex from: All charged tracks not in Brec,

constrain with Brec vertex, beam spot, and (4S) momentum

High efficiency: 95% Average z resolution ~ 180 m measured

from data)

Beam spot

Interaction Point

BREC Vertex

BREC daughters

BREC direction

BTAG directionTAG Vertex

TAG tracks, V0s

z

New tagging algorithm based on neural networks: inputs: leptons, K, slow (D* decay) and high-momentum tracks

5 mutually exclusive categories:

• Lepton - isolated high-momentum leptons;

• kaon I – high quality K, correlated K and slow • kaon II – low quality K or slow • Inclusive – unidentified leptons, low quality K, high-momentum tracks;

• Untagged Q = 28.1 + 0.7 % (~7% improvement)PRL87 (Aug01)


Tree level dominates and CP only from B 0-B 0 mixing

sin2 from charmonium states (b ccs)

)sin(2sinff

ff)(

-+

-+ tmtAd

fCP

f = f e-

i2f=±1

1)(

)(0

0

CP

CP

fBA

fBA

p

qfc

s

c

dd

bB0 K0

B0 -> J/ Ks

B0 -> (2S) Ks

B0 -> c1 Ks

B0 -> c Ks

f = -1

f = 1 B0 -> J/ KL

f = 1- 2RT B0 -> J/ K*0 (K*0 -> Ks 0)

RT = 16.0 + 3.5 % (PRL87)


Recent addition:B0 c Ks

where c K+K-

0 or

K+Ks -

Event yields and purity

Event Sample

Ntag Purity

J/ Ks(+-) 974 97%

J/ Ks(00) 170 89%

(2S) Ks 150 97%

c1 Ks 150 95%

c Ks 132 73%

Total (f = -1) 1506 92%

J/ KL 988 55%

J/ K*0 (Ks 0) 147 81%

All CP modes 2641 78%

Energy-substituted mass: 2cm2cmbeamES BpEm

Energy difference:cmbeam

cm0B

EEE


sin2 = 0.723 0.158

sin2 result

f =-1 f =+1

sin2 = 0.741 0.067 (stat) 0.033 (sys)

• Unbinned maximum likelihood fit: 34 parameters: sin2, mistag fract. (8), t resolution funct. (8), bkgnd (17) B = 1.542 ps, md = 0.489 ps-1 fixed (PDG 2002)

sin2 = 0.755 0.074

(hep-ex/0207042)


Asymmetry in b ccs modes with lepton tag

sin2 = 0.79 0.11

Golden mode (cc) Ks with lepton tag only

Ntagged = 220

Purity = 98%

Mistag fraction 3.3%

t 20% better than other tag categories


sin2 fit results by decay mode

Consistency of CP Channels: P(2) = 57%


Constraints in the () plane

One solution for is in excellent

agreement with measurements of unitarity triangle

apex

Method as in Höcker et al, Eur.Phys.J.C21:225-259,2001

= (1-2/2)

= (1-2/2)


Search for new physics in (cc)KS events

| f | = 0.948 0.051 (stat) 0.017

(syst)

Sf = 0.759 0.074 (stat) 0.032 (syst)

ACP (t) S f sin(mdt) C f cos(mdt)

Cf 1

f

2

1 f

2

Sf 2 Im

f

1 f

2

If another amplitude that

contributes with a

different phase:

In the measurement of sin2 we have assumed |f | = 1 (SM expectation)

Sf - f sin2 Cf 0

Fit |f| and Sf using the

clean (cc)Ks modes

(f =-1, Ntagged = 1506,

Purity = 92%):

Consistent with the Standard Model expectation of |f |=1 and nominal fit sin2 = 0.755 0.074 for (cc)Ks modes alone.


• B0 D*+D*-: same weak phase as b ccs (tree level);

small penguin contribution (<0.1 Tree);

not CP eigenstate (needs angular analysis)

The Cabibbo-suppressed modes (b ccd ) (I)

Ntagged= 102

Purity = 82%

B0

D* -

D* +

B0

D* -

D* +

Vcd

RT = 0.07+0.06+0.03

|+| = 0.98 0.25 (stat) 0.09 (syst)

Im(+) = 0.31 0.43 (stat) 0.10 (syst)

Im(+) measurement ~2.7 from BaBar sin2 in

charmonium, assuming no penguins.

+

Parameterize in terms of CP-odd () and CP-even (+) components and use:

| |= 1, Im( ) = -0.741

(hep-ex/0207072)

If penguins are negligible, then

Im(+) = - sin2


(hep-ex/0207058)

The Cabibbo-suppressed modes (b ccd) (II)

• B0 J/ 0 : also color-suppressed

Comparable tree and penguin

contribution ~ O(3)

Vcd

Tree: ~VcbVcd*

Penguin:~VcbVcd* +

VubVud*

Ntagged = 49 Purity = 59%f = + 1


Dominated by b sss gluonic penguins

sin2 from penguin mode B0 KS

|K| = 1 fixed

SK = -0.19 (stat) 0.09 (syst)

+0.52- 0.50

Small branching fraction O(10-5) Significant background from qq

continuum Using only K+K-

Ntagged = 66 Purity = 50%f = - 1

Cross check on B+ K +: SK = 0.26 0.27Analysis of B0 ’ KS in progress

If no new physics, SK = sin2

(hep-ex/0207070)

Same Weak phase as b ccs, but sensitive to new physics in loops


Interesting new measurements are being obtained on the open charm modes:

B 0D*+D*- (hep-ex/0207072)

and b penguin modes:B 0J/ 0 (hep-ex/0207058)

B 0 K0S (hep-ex/0207070)

Summary of sin2results

New measurement of sin2 from charmonium modes (88 x106 BB)

Submitted to PRL July 17, 2002(hep-ex/0207042)

Results have been improving by more than just luminosity gain

No hints of physics beyond the Standard Model yet, but lots of opportunities to challenge the theory with the increasing event statistics in BaBar

Million BB pairs

July 00

Feb 01

July 01Mar 02

July 02

sin2sin2 = 0.741 ± 0.067 (stat) ± 0.033 (syst) = 0.741 ± 0.067 (stat) ± 0.033 (syst)


sin2 from charmless B decays

Penguin contribution is non-negligible

measure sin2eff

mixing

*

*

ubud

ubud

VV

VV *

*

tdtb

tdtb

VV

VV

decay +

Tree (T)

Penguin (P)

)2sin(1

)sin(

eff2

/1

/12

CS

C

e ieieTP

ieieTPi

need BF from B -> +-, +0 and 00 and isospin analysis to obtain from eff

B0 +-


sin2 : B → , K, KK modes

• Small branching ratios (10-5-10-6)

lots of data needed

• Large background from continuum (qq)

events

use kinematic and topology of events to separate signal from

light-quark bg

i i

iii ppF2*** )cos(27.160.053.0

Fisher discriminant:

*

p*

• Ambiguity between and K

needs excellent particle ID (DIRC)

Data sample: 88M BB events


hypothesis

K hypothesis

K/ separation using the DIRC

• Double-gaussian PDFs built from the difference (c – c

exp)/s(c)

• K/ separation and PDF parameters measured using fully reconstructed

dataFor =85%: P(K->) = 1.7% P(->K) = 2.7 %

• Identification of h+h’- tracks as or K using the angle c measured in the

DIRC

KDDD 00* ,


Event yields and K asymmetry

sinsin

)()(

)()(00

00

T

P

KBBrKBBr

KBBrKBBrAK

CP

• Time-independent maximum likelihood fit to extract event yields and K asymmetry

no tagging or vertexing needed

Mode Yield BR (10-6) ACP(K)

B→ 157 + 19 4.7 + 0.6 + 0.2

B→ K 589 + 3017.9 + 0.9 + 0.7

-0.102 + 0.050 + 0.016

B→ KK 1 + 8< 0.6 (90% C.L.)

Direct CP

Preliminary

Submitted to Phys Rev (hep-ex/0207055)


mES and E distributionsPreliminary

Signal events are selected in the (mES,E) plane

same as for sin2 measurement

Bo -> Bo ->

K


1 p

s

Projection in sample of -selected events

qq+ K

S and C measurement

• Time-dependent unbinned maximum likelihood fit Same tagging and vertexing procedure as for sin2

)cos()sin(

)(00

00

tmCtmS

BNBN

BNBNtA

dd

tagtag

tagtag

S = 0.02 + 0.34 + 0.05

C = -0.30 + 0.25 + 0.04

Preliminary

Submitted to Phys Rev (hep-ex/0207055)


)(

)(21

1

1arccos22

0

00

2

BR

BR

Ceff

Extraction of from eff

Need to measure:

B+ ->+0, B0 ->00, B0 ->00

Grossman-Quinn bound

• Otherwise, put limit on BR(B0 ->00):

Isospin analysisGronau and London, Phys.Rev.Lett 65, 3381

(1991)

• B ->+-, +0 and 00 decays related by isospin

• (gluonic) penguins contribute only to I=0

• +0 has I=2 only tree amplitude only

(|AA)

2eff = 2 +


B+->+0 and B+->K+0 branching ratio

B+->+0 has pure tree amplitude and

no CP expected

• Usual charmless two-body analysis

• B0-> +- bg reduced by a

Fit region

ee→ qq

Mode Yield BR (10-6) ACP

B→

B→K

23211252122239

6.05.5 0.19.0

0.18.12 2.11.1

02.003.0 18.017.0

01.009.009.0

Simultaneous fit to /K

hep-ex/0207065

tight cut on E

Preliminary


B0->00 branching ratioPrelim

inary

B0->00 yield determined by unbinned ML fit:10

900 23

n

)%7.15.16(00

@ 90% CL

6000 106.3)( BBR

| – eff| < 510

Central value for BR:

66.03.0

7.06.0 10))()(6.1(

syststat

If BR as high as its central value, Grossman-Quinn bound not adequate isospin analysis is necessary

hep-ex/0207063

• Small signal expected

• Flavour tagging and event topology used to reduce qq bg

• B+->+0 bg reduced using a cut on m(+0) and E


B0->h: direct and indirect CP measurement

0000 and BBBB

CP

0

B

0

B

0B

0B

CP

BR = (28.9+5.4+4.3)x10-

6

)()(

)()(

hNhN

hNhN

NOT CP eigenstate

tmCCtmSSDD

Af dhhdhhh

CPh

tagBcossin

21)1(0

insensitive to CPK self

tagging

0 ,0 ,1 ,0 KKKK SSCC

Direct CP ACP and C = 0 Indirect CP S =

0


Event yields and charge asymmetry

Clear B0-> signal

• Maximum likelihood fit to extract yields and charge asymmetry:

2221

3433 147,413

KNN

background and qqBB

0.140.140.19 ( ) 0.11( )K

CPA stat syst 0.140.140.19 ( ) 0.11( )K

CPA stat syst

0.080.080.22 ( ) 0.07( )CPA stat syst 0.080.080.22 ( ) 0.07( )CPA stat syst

Preliminary

hep-ex/0207068

• Validation test: fit B and md using data

1-ps)09.051.0(

ps)12.059.1(

d

B

m

background and qqBB

qq

B0/B0->

B0/B0->

B = (1.540 + 0.014) ps

md = (0.503 + 0.006) ps-1

World AverageWorld

Average


Time-dependent asymmetry

qqBB and

only BB

0.180.19

0.250.25

0.45 ( ) 0.09( )

0.16 ( ) 0.07( )

C stat syst

S stat syst

0.180.19

0.250.25

0.45 ( ) 0.09( )

0.16 ( ) 0.07( )

C stat syst

S stat syst

Preliminary

hep-ex/0207068

dominated by uncertainties on B

background components

expected ~0.4 (from naïve factorization)

sensitive to strong phase differences

0.190.20

0.250.25

0.38 ( ) 0.11( )

0.15 ( ) 0.05( )

C stat syst

S stat syst


Direct CP violation

Direct CP can be expressed using the asymmetries:

CAC

CACA

BNBN

BNBNA

CP

CPCP

1)()(

)()(00

00

CAC

CACA

BNBN

BNBNA

CP

CPCP

1)()(

)()(00

00

meson from spectator quark

meson from spectator quark

Using previous results and their correlations:

A+- = - 0.82+0.31(stat)+0.16(syst)

A-+ = - 0.11+0.16(stat)+0.09(syst)


Summary of sin2and direct CP violation results

• Charmless two-body decays: branching ratios and CP asymmetries in B0->+-, K+- and K+K- (hep-ex/0207055) no evidence for large direct or indirect CP violation in +

branching fractions needed to extract from eff computed:

upper limit on BR(B0->00) (hep-ex/0207063)

B+->+0 and K+0 branching ratios (hep-ex/0207065)

still too early for significant constraint:

• Charmless three-body decays: first CP asymmetry measurement for B0->and B0->K(hep-ex/0207068)

| – eff| < 510

0.180.19

0.250.25

0.45 ( ) 0.09( )

0.16 ( ) 0.07( )

C stat syst

S stat syst

0.180.19

0.250.25

0.45 ( ) 0.09( )

0.16 ( ) 0.07( )

C stat syst

S stat syst

A+- = - 0.82+0.31(stat)+0.16(syst)

A-+ = - 0.11+0.16(stat)+0.09(syst)


Future: and sin(2+) (I)

with B ->D0(CP)K with B ->D0

(CP)K

W+

B+

b

uu

u

s

c

K+

D0

Vus

Vcb*

Colour allowed

B+

b

uu

c

K+

D0

W+

u

sVcs

Vub*

Colour suppressed

1||)(0 ieAKDBA

ii eeAKDBA 2||)( 0

)( *uscbVV

)( *csubVV

)%20.035.031.8()(

)(0

0

DBBr

KDBBrR

0 00.090.070 0

( ) ( )0.17 0.23

( ) ( )

CP CPCP

CP CP

Br B D K Br B D KA

Br B D K Br B D K

data sample 75

fb-1

hep-ex/0207087

Preliminary


Future: and sin(2+) (II) Preliminary

B ->D*//a1

h+W+

B0

b

dd

u

d

c

D*-

Vud

Vcb*

Cabibbo allowed

W+

B0

b

dd

c

d

u

h-

Vcd

Vub*

Cabibbo suppressed D*+

Time evolution of B0->D*-h+ and B0->D*+h- related to sin(2+)

• For precise measurement, need many events

• D*a1 mode has the largest BR (~1.3%)

• use partial reconstruction:

Only the slow from D*->D0 decay and the //a1 (a1->0) are reconstructed

If only the D0 is missing, in the (4S) frame the B direction lies on the surface of a cone

Averaging over this surface, the missing mass mmiss can be defined

P*(,,a1)P*

P*D0

P*B

Signal: mmiss peaks to D0 mass

Bg events: broader distribution


B ->D*

t(ps)

Continuum

Comb. BB

Peak. BB

Signal

Nsig = 6971+241

First steps: B0 lifetime using D* and D* decays

B = 1.616+0.064(stat)+0.075(syst) pshep-ex/0203036

B = (1.540 + 0.014) ps

World AverageB = 1.510+0.040(stat)+0.038(syst)

ps hep-ex/0203038

Validation for the partial reconstruction technique

B ->D* Nsig = 5521+251

B extracted using an unbinned maximum

likelihood fit

data sample

20.7 fb-1


data sample

20.7 fb-1

PDG: (1.30+0.27)%

BF = (1.20+0.07+0.14)%

BF = (1.20+0.07+0.14)%

Signal yield: 18400+1200

Preliminary hep-ex/0207085

• data on-reso (off-reso subtr.)

signal+BB bg MC

BB bg MC only

D*a1 branching fraction measurement

• Continuum background rejected using a neural network technique

exploit the different topologies between qq events (jet structure) and B events (spherical)

• mmiss distribution obtained from off-reso data subtracted from that obtained on on-reso

• result fitted with a combination of:

BB Monte Carlo events

signal Monte Carlo events

B ->D*a1


Summary: B ->D0(CP)K and B0 ->D*(n)

Analyses just begun, still lot of work to do !

• B -> D0(CP)K mode:

ratio of branching fraction for B->D0K and B->D0 modes

first measurement of CP asymmetry in B->D(CP)

K (hep-ex/0207087)

• B -> D*(n) mode : B0 lifetime using D* and D* decays (hep-ex/0203038, hep-ex/0203036)

branching fraction of B0 -> D*a1 decay channel (hep-ex/0207085)

R= (8.31+0.35+0.20)%

ACP= (0.17+0.23 )+0.0

9

-0.07

BF = (1.20+0.07+0.14)%

B = (1.533+0.034+0.038) psCombined measurement:


Conclusions (I)

Extremely productive time for B physics with

BaBar !More still to

come !BUT

New measurement of sin2 from charmonium modes Submitted to PRL July 17, 2002

(hep-ex/0207042)sin2sin2 = 0.741 ± 0.067 (stat) ± 0.033 (syst) = 0.741 ± 0.067 (stat) ± 0.033 (syst)

First steps to analyze decay modes related to and sin(2+) first measurement of CP asymmetry in B->DK (hep-ex/0207087) B0 lifetime with D* and D* decays (hep-ex/0203038, hep-ex/0203036) branching fraction of B0->D*a1 decay (hep-ex/0207085)

No evidence for large direct or indirect CP violation in B0->+ Measurement of the branching ratios for B+-> +0,K+ (hep-ex/0207065)

Upper limit on BR(B0-> 00) and constraint on |-eff| (hep-ex/0207063)

CP asymmetry in B0/B0->+ decay (hep-ex/0207068)

(hep-ex/0207055)

BaBar and Belle’s sin2 results have convinced the physics community that CKM is the dominant

source of CP violation


Conclusions (II)

More exciting physics results are on their

way !

0

100

200

300

400

500

Year

Inte

gra

ted

Lu

mi [

fb-1

]

024681012141618

Pea

k L

um

i [10

**33

]Yearly Lumi

Cumulative Lumi

Peak Lumi

Yearly Lumi 2 23 40 70 95 110 70

Cumulative Lumi 2 25 65 135 230 340 410

Peak Lumi 1 2 5 7.5 10 12 17

1999 2000 2001 2002 2003 2004mid

2005A lot more to do with the 100 fb-1 of data already recorded and those still to come in the next run

starting this fall• higher precision in the sin2 measurement

• measurement of and better knowledge of |Vub| and |Vcb| rare decays (possibility to probe new physics) Charm physics (D0 mixing, CP, ….) tau results

• other very interesting physics results:


Tagging performance

Category Efficiency () Mistag Fr. () Mistag Q=(1-2)2

Lepton 9.1 0.2 3.3 0.6 -1.4 1.1 7.9 0.3

KPiorK 16.7 0.2 9.9 0.7 -1.1 1.1 10.7 0.4

KorPi 19.8 0.3 20.9 0.8 -4.2 1.1 6.7 0.4

Inclusive 20.0 0.3 31.6 0.9 -2.0 1.2 2.7 0.3

Total 65.6 0.5 28.1 0.7


Sources of Systematic Error

sin2Description of background events 0.017

CP content of background componentsBackground shape uncertainties

Composition and content of J/ KL background 0.015

t resolution and detector effects 0.017Silicon detector alignment uncertaintyt resolution model

Mistag differences between BCP and Bflav samples 0.012

Fit bias correction 0.010Fixed lifetime and oscillation frequency 0.005TOTAL 0.033

Steadily reducing systematic error: July 2002 = 0.033July 2001 = 0.05


sin2 in subsamples


Cross-check on data control samples

Observed no asymmetry as expected


CP composition of B0 D*+D*-

We measure CP odd fraction (corrected for acceptance) to be small:

R = 0.07 0.06 (stat) 0.03 (syst)

dd cos tr

34

1 R sin2 tr 32

R cos2 tr


The Cabibbo-suppressed modes (b ccd)

D* _

D+

D* _

B0

B0

D*+

D _

D*+

D _

D+

CPconjugation

strongphase

D*D 56 fb-1

Ntagged= 85Purity = 52%

S+- = -0.43 1.41 0.20

C+- = 0.53 0.74 0.13

S-+ = 0.38 0.88 0.05

C-+= 0.30 0.50 0.08Update to full data set in progress

• B0 D*+D- :

Not a CP eigenstate

• possible strong phase contributions;

• different decay time distributions for :

B0 D- D*+

B0 D*- D+


Validation of tagging, vertexing and fit procedure

• Use B0 ->K events:

T=tag charge, Q=K charge

)cos()21(14

)(/

, tmwTQe

tf d

tK

QT

same sample as for CP asymmetries

B and md floating in the fit

B = (1.56 + 0.07) ps

md = (0.52 + 0.05) ps-1B = (1.540 + 0.014) ps

md = (0.503 + 0.006) ps-1

World Average

Projection in sample of -selected events

Recent Results from B A B AR

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