L.Lista INFN Sezione di Napoli

Luca ListaGr. I , 10/9/01

L.Lista INFN Sezione di Napoli

Results of BResults of BAABBARAR experiment experiment on CP violation and B physicson CP violation and B physics


OutlineOutline

(4S)• Experimental set-up

• CP asymmetries sin2

sin2eff

• B Mixing and lifetime• Rare B decays• Conclusions

(Many topics will be skipped)


Low Energy Ring[e+, 3.1GeV]

High Energy Ring[e-, 9.0GeV]

PEP-II at SLACcenter of mass energy M(4S) =10.58 GeV/c2

= 0.56

BaBar

The PEP-II B-FactoryThe PEP-II B-Factory


Integrated LuminosityIntegrated Luminosity32 Million Y(4S) decays recorded

• BaBar recorded: 37.7fb-1 4.05 fb-1 off peak

• Top luminosity:• 3.4x1033 cm-2s-1

• Design:

3x1033 cm-2s-1


The BaBar detectorThe BaBar detector

ElectromagneticCalorimeter

6580 CsI(Tl) crystals

Instrumented Flux Return19 iron / 18-19 RPC layers

Drift Chamber40 axial stereo

layers

1.5T solenoid

DIRC (PID)144 quartz bars

11000 PMTs

e-

e+

Silicon Vertex Tracker5 layers, 2-sided Si strips


• Unitarity relations on matrix

elements lead to a triangle in the complex plane

The Unitarity TriangleThe Unitarity Triangled s b

u

c

t

V V V

V V V

V V V

ud us ub

cd cs cb

td ts tb

0*** tbtdcbcdubud VVVVVV

*

*td tb

cd cb

V VV V

*

*ud ub

cd cb

V VV V

1

B=(1,0)

C=(0,0)

A=(,)

• Quark mixing is described by the CKM matrix


CP violation at asymmetric B factoryCP violation at asymmetric B factory

CP violation via mixing interference

)(sin2sin)( tmtAdBCPCP

@t=0

B0

B0

t (ps)

FF

BB00 ffCPCP

BB00

b

dW W

d

b

t

tB0 B0)(sin)(cos

))(B())(B())(B())(B()(

00

00

tmStmCftftftfttA

dCPdCP BfBf

CPdCPd

CPdCPdCP

CP

CP

CPCPf

fff A

Apq

For “golden” bccs modes:

2

2

2

||1Im2

||1||1

CP

CP

CP

CP

CP

CP

f

ff

f

ff

S

C

fCP eigenvalue e-2i


sin2sin2: Improvements w.r.t. run I: Improvements w.r.t. run I

• More data!• Added new modes

c1KS, J/K*0

• Improved reconstruction efficiency Improved tracking ~ +30% KS reconstruction eff.

• Improved vertex resolution New alignments More elaborated vertex algorithm

• Optimized KL selection taking into account the background CP asymmetry Maximize (S+AB/ASB)2/(S+B), not S2/(S+B)


All sin2All sin2 CP modes CP modes

N=724 B0J/K0S

B0(2S)K0S

B0cK0S

B0J/K0L

IFR

EMC

CP = -1

CP = +1

KL momentum not measuredE determined from B mass and beam energy constraints N=129

(65% pur.)

N=128(56% pur.) Golden modes:

~30% higher efficiency than run 1: KS efficiency improved


Fully reconstructed B flavor modesFully reconstructed B flavor modes

• Cabibbo favored decays: B0Da

B+ D()0 + , J/K+, (2S)K+


CP modes: FCP(t) e-|t|/

B ( 1 CP sin2sin md t )

Flavour specific modes: Fflav

(t) e-|t|/B ( 1 cos md t )

B1 = B0

ze-e+

B01 partially reconstructed

flavor tagged B02 fully reconstructed

D*+ - or J/K0S

B1 = B0

unmixed B0 B0

mixed B0B0 or B0B0

Mixing and CP asymmetry of BMixing and CP asymmetry of B00/B/B00


Imperfect tagging and resolutionImperfect tagging and resolution

B0

B0

unmixed mixed

e-|t|/B (1 CP

sin2sin md t)

e-|t|/B (1 cos mdt)

e-|t|/B (1 CP D sin2

sin md t)

e-|t|/B (1 D cos md t)

e-|t|/B (1 CP D sin2

sin md t) R(t)

e-|t|/B (1 D cos mdt)

R(t)

D = 1-2w = dilution, w = wrong tag fractionR(t) = resolution function

Imperfecttagging

Imperfectresolution


Fitting ProcedureFitting Procedure

Parameter # samplesin2 1 CP w and w 8 Flavort resolution 16 Flavor, CP

Bkgd w 8 SidebandsBkgd t 12 Sidebands

• Unbinned maximum likelihood fit• Mistag and resolution: empirical distribution

fitted from data• fixed in the fit:

md = 0.472 ps-1 (was extracted from the same fit in Run-I analysis)tB = 1.548 ps

Separate for Run I & II Largest correlationWith sin2: 13%


Flavor misid. measurementFlavor misid. measurement

D=1-2wQ=(1-w)2

(sin2 1/(Q)

w

Neural network mainly to recover unidentified leptons and use soft pions from D*


sin2sin2 result result

sin2 = 0.59 ± 0.14stat ± 0.05syst


Comparison of different samplesComparison of different samples

Submitted toPhys. Rev. Lett.On July 5 2001


Unitarity triangle Unitarity triangle

21

sin2 = 0.59 ± 0.14stat ± 0.05syst


Search for direct CP violationSearch for direct CP violation

• Assuming more than one amplitude dominate the decay:

|| may be 1

• Only CP = -1 used High purity, no assumption needed on CP of the background

No evidence found (none expected from SM)

)sin()cos()( tmStmCtAdCPdCP BfBfCP

2

2

2

||1Im2

||1||1

CP

CP

CP

CP

CP

CP

f

ff

f

ff

S

C

||=0.93 ± 0.09 ± 0.03


• 0.03 from vertexing• 0.03 from tagging• 0.02 from background

Total 0.05

SystematicSystematic error errorss


mmdd measurementmeasurement

md =

0.519 ± 0.020stat ± 0.016syst ps-1

preliminary

Run I only


Lifetime resultsLifetime results

0 = 1.546 0.032(stat) 0.022(syst) ps = 1.673 0.032(stat) 0.022(syst) ps0 / = 1.082 0.026(stat) 0.011(syst) common resolution

t (ps) t (ps)

background

B B0/B0


Charmless Hadronic DecaysCharmless Hadronic Decays

• Physics motivations

b ud(s)

Vub

Vud(s)

B0 { }

} (K)

d d

u

bB0 { dud(s)

}

} (K)

d

u

tW

W

Vtb

Vtd(s)

Cabibbo suppressed tree diagram

Penguin diagram

• Significant penguin contribution

• Direct CP violation studies

• Measurement of from time-dependent asymmetry + isospin analysis

• Possible field for new physics…


Two body Branching fractionsTwo body Branching fractionscontrol sample:D*D0, D0K

> 3 sigma

p (GeV/c) Run I only


CP violation in BCP violation in B00: sin2: sin2effeff

• Neglecting penguin pollution: = f e-2i() = f e2i C=0, S= sin2

• Considering penguin diagrams: || 1 C 0, S= sin2eff = sin2 f (Penguin / Tree)

Extraction of sin2 requires the study of B0 and B0

• Fitted simultaneously with branching fractions• Dilutions and time resolutions taken from sin2 fit

S = 0.03 +0.53-0.56 0.11

C = 0.25 +0.45-0.47 0.14

ACP(K) = -0.07 0.08 0.02

preliminary

expected ~0.3

Run I + II


Radiative Penguin: B Radiative Penguin: B K* K*

Signal:

B0 K*0, K*0 K+-

Backgrounds:

e+e- qq

e+e- qq X 0

• Sensitive to top quark couplings CKM matrix elements

Vtd,Vts

• Sensitive to New Physics SUSY, Charged Higgs

• No CP asymmetry in the Standard Model (< 1%) Possible sources

beyond SM


BB00 K* K*00: yield and branching ratio: yield and branching ratio

• Nsignal = 139.2 13.1 events• Br(B0 K*0) = (43.9 4.1 2.7) 10-6

• Br(B Kl+l-) < 0.6 10-6 (90% C.L.)• Br(B K*l+l-) < 25.7 10-6 (90% C.L.)

B0 K*0 K*0 K+


BBK, BK, BK* K* • Penguin dominated

B+K+ = (7.7 +1.6-1.4 0.8) 10-6

B+ < 1.4 10-6 (90% C.L.)B+ K*+ = (9.7 +4.2

-3.4 1.7) 10-6

• Possible measure of sin2B0 K*0 = (8.6 +2.8

-2.4 1.1) 10-6

B0 K0 = (8.1 +3.1-2.5 0.8) 10-6

Max Lik. Fit projections


B++ = ( 6.6 +2.1-1.8 0.7 ) 10-6

B0K0 < 12 10-6

B+K+ = ( 70 8 5 ) 10-6

B0K0 = ( 42 +13-11 4 ) 10-6

B+K*+ = ( 22.1 +11.1-9.2 3.3 ) 10-6

B0K*0 = ( 19.8 +6.5-5.6 1.7 ) 10-6

B0K*0 < 28 10-6

B+0K+ < 39 10-6

B+0+ < 39 10-6

B+K+< 54 10-6

B++< 22 10-6

B0=( 49 13 +6-5 ) 10-6

B0a0(980)Br(a0 = ( 6.7 +3.2

-2.7 1.3 ) 10-6

Quasi 2-body and 3-body decaysQuasi 2-body and 3-body decays

Potential for sin2

First

Observation


Search for direct CP violationSearch for direct CP violation

ws

ws

iiNEWSM

iiNEWSM

eeAAKBeeAAKB

wsSM

NEW

CP

AA

KBKB

KBKBA

sinsin

22

22


B B D*D D*D((**))KK• Study of the bccs transition

• Experimental inclusive estimate from from BDSX, (cc)X, CX, CX (ALEPH, CLEO) Br(bccs) ~ 15.82.8 %

• Theoretical calculation can’t determine this low value together with inclusive s.l. branching ratio (bcW) Three-body B DDK can contribute

• Study of color suppressed modes (B D*D*K)

Color allowed Color suppressed


B B D*D D*D((**))KK

B0 (all modes)NS = 18021

B+ (all modes)NS = 11715

B D*D*K

NS = 8.23.5

• Reconstructed decays: D*+ D0+ D*0 D00

D*0 D0 D0 K-+ D0 K-+0 D0 K-+-+ D+ K-++

• Br(B D*D0K) = (0.280.070.05)10-2

• Br(B D*D*K) = (0.680.170.17)10-2

• Br(B D*D*K) = (0.340.160.11)10-2

First observation of color suppressed mode other than B (charmonium)X


ConclusionsConclusions

• sin2 extracted from 37.7 millions of BB events

sin2 = 0.59 ± 0.14stat ± 0.05syst

• CP violation established at 4.1 level• First measurement of CP violation in B0

• High precision measurements of mixing parameter and lifetimes

• High precision measurements of B decays branching fractions Many newly observed decays

• Most of the results are still statistically limited


Backup slidesBackup slides


J/J/ K* angular analysis K* angular analysis

|A|2 = 0.1600.032 0.014 CP odd, P wave

|A|||2 = 0.2430.034 0.017 CP even, S+D wave

|A0|2 = 0.5970.028 0.024 CP even, S+D wave

= arg(A/A0)=0.170.16 0.07

|| = arg(A|| /A0)=2.500.20 0.08

Time dependent CP asymmetry dilution factor: D = 1 – 2 |A|2 = 0.680.10

• L=0,1,2 waves• Both CP even and odd amplitudes are

present• Measurement of sin2 is possible

from angular analysis

Channels with 0

Channels without 0

f ( costr, cosK*, tr ) =

f1 |A0|2 + f2 |A|||2 + f3|A|2

+ f4 Im(A||* A) + f5 Re (A0* A||)

+ f6 Im (A0* A)

J/ rest frameK* decay plane


BB00 D* D*++D*D*

• Cabibbo suppressed decay• A measurement in bccd of CP violating

time-dependent asymmetry can be performed from angular analysis Possible penguin contamination

• Measurement of sin2 independent from B0J/K

S

Significant deviations from B0J/KS

measurement of sin2 may be indication of new physics

• Branching ration measurement of B D(*)+D(*)-:

Tree diagram

Penguin contribution


BB00 D* D*++D*D*

Br(B0D*+D*-) = (8.0 1.6 1.2)10-

4

Background sample(6.240.49 expected in signal box)

Signal box(38 events)


Inclusive Inclusive CharmoniumCharmonium decays decays

• Inclusive J/ branching ratio:Br(BJ/X) = (1.0440.013 0.028) 10-2

Br(BJ/X dir.) = (0.7890.010 0.034) 10-2

• Inclusive (2S) branching ratio:Br(B (2S) X) = (0.2750.020 0.029) 10-2

(2S)ll branching ratio:(2S) ee(7.8 0.9 0.8)10-3

(2S) (6.7 0.8 0.7)10-3

• Inclusive c branching ratios:Br(B c1 X) = ( 0.378 0.034 0.026 ) 10-2

Br(B c1 X dir.)= ( 0.353 0.034 0.024 ) 10-2

Br(B c2 X) < 0.2110-2 @ 90% C.L.

= ( 0.137 0.058 0.012 ) 10-2

Br((2S) J/assumed from PDG

p*J/ < 2 GeV/c

J/ ee

J/ b

s, dB0, B

X

J/, (2S), c

d, u

cc

W-


• Main motivation: Channels are used for CP

violation measurements Kinematics selection:

Energy substituted mass

• Independent on particle mass hypotheses

Energy difference in the center of mass

Exclusive B decaysExclusive B decays

2,4 cmBES psm

2sEE B

B0J/ 0

First observation:B0c1 K*0


J/J/ production in continuum production in continuum

.).%90(103.4

21.021.052.24

/)4(

/

LCB

pb

XJS

XJee

Color singles prediction: 0.8 pb A –0.8,

NRQCD (c.o.) prediction: 2.8 pb 0.6<A<1.0

Angular distribution 1+A cos2*

• First observation of J/ production in continuum (4S) events with p*J/>2 GeV/c Off-resonance events

• A (all E*) = 0.25 0.19 • A (p*>3.5 GeV) l= 0.62 0.39


Branching ratios resultsBranching ratios resultsMode Br (10-4)B0 J/ 0 0.20 0.06 0.02

B0 J/ K*0 12.4 0.5 0.9

B+ J/ K* 13.7 0.9 1.1

B+ J/ K 10.1 0.3 0.5

B0 J/ KKL 6.8 0.8 0.8

B0 J/ KKS00 9.6 1.5 0.7

B0 J/ KKS+ 8.5 0.5 0.6

B0 J/ KAll 8.3 0.4 0.5

B0 c1 K* 4.8 1.4 0.9

B0 c1 K 5.4 1.4 1.1

B+ c1 K+ 7.5 0.8 0.8

B+ (2S) K+ 6.3 0.5 0.8

B0 (2S) K0 6.8 1.0 1.1Br(B+J/)/Br(B+J/K ) =

(3.910.78 0.19)10-2

RUN 1:22.7 MBB


mmdd measurement: the di-lepton analysismeasurement: the di-lepton analysis

e-e+

zl+or l-

l+or l-

N+ –, – + – N+ +, – –

N+ –, – + + N+ +, – –

A(z)=

Asy

mm

etry

md = 0.499 ± 0.010 ± 0.012 ps-1


Semileptonic B decaysSemileptonic B decays

• Determine the sign of the B from a sample of ~14000 fully reconstructed B

B0D(*), D(*), D(*)a1, J/K*0

BD(*), J/K, (2S)K

• Lepton identified in the decay of the other B

B+ B0

0.030.100.99

)B()B(

4.05.04.10 )B(

0

eXBeXB

eXB

Mixing corrected


bbss, B, B00 • Semi-exclusive study

Sum of exclusive modesK+n(n=1,2,3)

mES for 0.6 <mhad < 2.0 GeV

• Theoretical exp.: ~ 10• Br(B0) < 1.7 x 10-6 90% C.L.• PDG: Br(B0 ) < 3.9 x 10-5 90% C.L. (L3)

Branching ratio measurementcoming soon…B0

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