L.Lista INFN Sezione di Napoli

Luca ListaNapoli, 20/6/01

L.Lista INFN Sezione di Napoli

Results of BResults of BAABBAR experiment AR experiment on CP violation and B physicson CP violation and B physics


OutlineOutline

(4S)• Experimental set-up

• Charmonium decays

• B lifetime measurement

• Mixing and CP asymmetry• Rare B decays• Future perspective and

Conclusions


Has delivered 23.7 fb-1 from Oct. 99 to Nov.2000

Low Energy Ring[e+, 3.1GeV]

High Energy Ring[e-, 9.0GeV]

at Stanford Linear Accelerator Center (California)

center of mass energy M(4S) =10.58 GeV/c2

= 0.56

BaBar

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


Performance during the 99-00 runPerformance during the 99-00 run

Parameter Design Achieved Typical# of bunches 1658 1658 553-829LER current 2.14 A 2.14 A 1.35 AHER current 0.75 A 0.92 A 0.73 ABeam size x 222 m 190 m -Beam size y 6.7 m 6.0 m -Fill time 6 mn 8 mn 10 mnTop-off time 3 mn 2 mn 3 mnLER lifetime 4 hrs@2A 3.3 [email protected] 3.0 [email protected] lifetime 4 hrs@1A 11. [email protected] 9.0 [email protected] 3.0 1033 cm-2s-1 3.3 1033 cm-2s-1 2.5 1033 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


The Silicon Vertex TrackerThe Silicon Vertex Tracker

Beam pipelayer 1,2layer 3layer 4layer 5

Beam bending magnetshigh radiation area

• 5 layers: 20o< <150o;

R= 3.2, 4, 5.4, 9.1-12.7, 11.4-14.4 cm• Single hit resolution: 10-15 m


The Drift ChamberThe Drift Chamber

• 40 axial and stereo layers for Z measurement • small hexagonal cells (11.9 x 19.0 mm)• 80%:20% helium:isobutane

(pT)/pT = 0.13% pT 0.45%


The Cherenkov detector (DIRC)The Cherenkov detector (DIRC)

• Internally reflected Cherenkov radiation

• ~11000 phototubes


• Identification of e±,,0

• Energy resolution:

The Electromagnetic CalorimeterThe Electromagnetic Calorimeter

%9.1%3.2)(4

EE

E


The Instrumented Flux ReturnThe Instrumented Flux ReturnMuon and KL reconstruction18/19 RPC planes~53000 electronic channels


B-countingB-counting

• The determination of B decays branching ratios requires a precise estimate of the number of produced (4S)BB events

• Counting of Multi-Hadron events

• Correction factor: = 0.99620.0027 Different efficiencies for and MH on and off-

resonance• 22,700,000 BB events, 1.7% sys. error

off

offMH

MHBB NNNNN


Inclusive Charmonium DecaysInclusive Charmonium Decays

Effi

cien

cy

muons

pionsE

ffici

ency

b

s, dB0, B

X

J/, (2S), c

d, u

cc

W-

• J/, (2S) and c are reconstructed in final states containing leptons

• Different selection purity for different decays


Inclusive J/Inclusive J/ decays decays

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

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

• p*: J/ momentum distribution in the (4S) system B system coincides with (4S) within 250 MeV

p*J/ < 2 GeV/c

J/ ee J/


J/J/ momentum spectrum momentum spectrum

continuum

BB events


J/J/ production in continuum production in continuum

.).%90(103.4

21.021.052.24

/)4(

/

LCB

pb

XJS

XJee

Color singles prediction: A –0.8, 0.8 pb NRQCD (c.o.) prediction: 0.6<A<1.0, 2.8 pb

Angular distribution 1+A cos2*

• First observation of J/ production in continuum BB events rejected by p*>2 GeV/c Rejection of Initial State Radiation

• Ntracks, Etot, R2

• A (all E*) = 0.250.19 • A (p*>3.5 GeV) l= 0.620.39


Br( B (2S) X ) = (0.2750.020 0.029) 10-2

Inclusive Inclusive (2S) decays(2S) decays

p* < 1.6 GeV/c

(2S) ll, J/

(2S) ee (8.1 0.9 0.9)10-3

(2S) (7.0 0.8 0.9)10-3

• Assuming PDG values for (2S) J/:

(2S) ll branching ratio measurement


Inclusive Inclusive c c decaysdecays

• 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

c2 (?) c2 (?)


• Kinematics selection: Energy substituted mass

• Independent on particle mass hypotheses

Energy difference in the center of mass

Exclusive B decaysExclusive B decays

• Motivation: Several channels are used

to constrain the unitarity triangle

Charged modes may exhibit direct CP asymmetry

Probe of non perturbative QCD

Theoretical prediction available for many decays in the factorization hypothesis

2,4 cmBES psm

2sEE B


Golden CP mode: BGolden CP mode: BJ/J/KK00SS


BBJ/J/KK00LL

• KL reconstructed as neutral deposit in the I.F.R. or E.M. Calorimeter

• 1.4 < p*J/ < 2.0 GeV/c

• No KL momentum measurement• E is determined

assuming the mB mass constraint


Selected rare channelsSelected rare channelsFirst observation:B0C1 K*0B0J/ 0


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 1.1


BaBar compared to PDG 2000BaBar compared to PDG 2000


J/J/++ / J/ / J/KK++

• Cabibbo and color suppressed tree diagram possible CP asymmetry from penguin contribution

• Unbinned maximum likelihood fit based on kinematical variables:

Br(B+J/)/Br(B+J/K ) =(3.910.78 0.19)10-2

0 2 4 6 8 10

Br(B+ to JpsiPi+) / Br(B+ to Jpsi K+)

CLEOCDFPDGBaBar

( 5.2 2.4 ) %

( 5.0 0.1 ) %

+1.91.7

( 5.1 1.4 ) %


Z

B1 partially reconstructedz ~ 140 m

BB±± and B and B00/B/B00 lifetimes lifetimes

e- e+

9 GeV 3.1GeV

= 0.56z

cB 260 m

B2 fully reconstructedz ~ 60-100 m

• One B is fully reconstructedin a B0 or B mode • Measure both B vertices• Fit for t z/c B

lab

ideally PDF(t) exp(-|t|/B)

• Novel method for asymmetric e+e- machines• Different systematics from previous measurements• Detailed understanding of resolution function needed


The 99-00 data sampleThe 99-00 data sample

B0/B0 B

22.7 106 BB pairs recorded

6967 ± 95 purity 90%

7266 ± 94purity 93%

B0 D(*)+ - D(*)+- D(*)+a1

-

J/K*0

B- D(*)0 - J/K- (2S)K-


Resolution function fitted on data:R(t)=f*Gaus(s)+(1-f)*Gaus(s)Exp(k)

identical for B± and B0/ B0

Unbinned maximum likelihood fit:

psig from mass distribution fit

Bkg description fromside-band events

B0/B0 MC

t residual/ t

Fitting procedureFitting procedure

])O( )())([(

)()(P.d.f./

/

tctRbetap

tRept

bgdt

bgd

sigt

sigbgd

B


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

BB0/B0

preliminarypreliminary


Other lifetime ratio measurementsOther lifetime ratio measurements


• 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

• coherent production: Y(4S) BB clock starts at 1st B decay

Integrated asymmetry = 0time dependent analysis required

CP violation via mixing interference in bccs

)sin(2sin)()()()()(

)]sin(2sin1[)( /

tmtFtFtFtFtA

tmetF

dCP

CPCP

CPCP

CP

dCPtCP B

@t=0

B0

B0

t (ps)

FF

BB00 J/J/KK00ss

BB00

b

dW W

d

b

t

tB0 B0


The 99-00 data sample: CP modesThe 99-00 data sample: CP modes

J/K0S (

J/K0S ()

(2S)K0S (

CP = -1425 ± 22 purity 94%

J/K0L

CP = +1

199 ± 23 purity 45%


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

flavour 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


Neural network mainly to recover unidentified leptons and use soft pions from D* • NT1: = 7.7 0.4% • NT2: = 13.7 0.5% Total = 68.9 1.0%

Tagging the flavour of the BTagging the flavour of the B00CP/flavCP/flav

Look at the second B in the event• leptons: b l- , b l+

p*>1.0 GeV/c (e±), p*>1.1 GeV/c (±) = 10.9 0.4%• kaons: b K- , b K+

= 36.5 0.7%


Imperfect tagging and resolutionImperfect tagging and resolution

B0

B0

unmixed mixed

e-|t|/B (1 CP

sin2sin md t)

perfect tagging/ resolution

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

imperfect tagging/ perfect resolution

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

sin md t)

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

imperfect tagging/imperfect resolution

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

sin md t) R(t)

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

R(t)


unbinned maximum likelihood fit:

Free parameters #par sample

sin2 1 CP md 1 flavour

D(B0) & D(B0) 8 flavour & CP

Sig. t resolution 9 flavour & CP

Bkg. t resolution 3 flav & CP side-bands

Bkg. composition 13 flavour side-bands

Bkg. composition 1 CP side-bands

• md : flavour specific sample • sin2 : flavour specific +CP samples

Mainly constrainedby high statflavour sample

Empirical descriptionfitted on data

largest correlation with sin2: 7.6%

Fitting ProcedureFitting Procedure


Flavour misid. measurementFlavour misid. measurement

D = 1 - 2 w Fraction ofwrongly taggedevents

Check w with a time-integrated method (events with |t|<2.5 ps to optimise (w))On the same sample and on ~11000 D*l

(sin2 1/(Q)

kaons

leptons

NT1

NT2


mmdd measurementmeasurement

md =

0.519 ±0.020stat±0.016syst ps-1


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


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


sin2sin2 results results

sin2 = 0.34 ± 0.20stat ± 0.05syst

sin2=0.25±0.22stat sin2=0.87±0.51stat


sin2ln

(L/L

max

)

CP = -1

CP = +1

sin2=0.25±0.22stat

sin2=0.87±0.51statcombined result

Time dependent asymmetryTime dependent asymmetry


sin2 sin2

Cross-checks: sin2Cross-checks: sin2 on sub-samples on sub-samples


sin2sin2 systematic uncertainties systematic uncertainties


World average for sin2World average for sin2


Unitarity triangle Unitarity triangle

21

sin2 = 0.34 ± 0.20stat ± 0.05syst


J/J/ K* K*00 angular analysis 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

|A|2 + |A|||2 + |A0|2 = 1

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

• Measurement of sin2 is possible from angular analysis


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

(a) Raw measurement(b) Acceptance correction(c) “ “ + mES fit(d) “ “ + (Self) Feed Across

Indication of FSI


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


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)


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…


Identifying K and Identifying K and

• Particle identification in the DIRC

D*+D0, D0K-+ control sample

> 3 sigma

p (GeV/c)

p (GeV/c)


Background RejectionBackground Rejection• Continuum events rejection

Combination of event shape variables Thrust axes (B vs rest of event)

• Background control samples E sidebands Off-resonance data D*+D0, D0K+ control sample

signal

D0+

E sidbands background

background

signal


Two Body Charged ModesTwo Body Charged Modes

• B hh

Mode Yield, significanceBranching ratio

K 169 17+12-17, 15.8

(16.7 1.6 +1.2-1.7)10–6

41 10 7, 4.7(4.1 1.0 0.7)10–6

KK 8.2 +7.8–6.4 3.3, 1.3

< 2.510–6 (90%C.L.)

Unbinned Maximum Likelihood Fit results

mES (GeV/c2) E (GeV)

Fit projections(after a likelihood ratio cut)

K


Two Body Charged + Neutral ModesTwo Body Charged + Neutral Modes

• B 0 h


37 +15-13, 3.4

(5.1+2.0-1.8 0.8)10–6

K 75 +14-13, 8.0

(10.8 +2.1-1.9

+1.0-1.2 )10–6



Fit projections


Two Body with K-shortTwo Body with K-short


K0 59 +11-10, 9.8

(18.2 +3.3-3.0

+1.6-2.0)10–6

K0K 0 (< 8), 0< 2.610–6 (90%C.L.)

K00 17.9 +6.8-5.8, 4.5

(8.2 +3.1-2.7

+1.1-1.2)10–6



Fit projections• B K0h+, K00


Direct CP AsymmetriesDirect CP Asymmetries

• Self tagged modes:

• KA = - 0.19 0.10 0.03 [ -0.35, -0.03 ], 90%C.L.

• KA = 0.00 0.18 0.04 [ -0.30, +0.30 ], 90%C.L.

• KA = - 0.21 0.18 0.03 [ -0.51, +0.09 ], 90%C.L.

• All asymmetries compatible with 0 within current errors


B0

B+h+ < 24 10-6 ( 90% C.L. )B0K0 < 14 10-6

B+K+ ( 62 18 8 ) 10-6

B0K0 < 112 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

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


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


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) = (4.39 0.41 0.27) 10-5

• Br(B K+e+e-) < 12.8 10-6

• Br(B K++-) < 8.3 10-6

• Br(B K*0e+e-) < 24.7 10-6

• Br(B K*0+-) < 25.7 10-6 (90% C.L.)

B0 K*0 K*0 K+


• K*0 KK*0 K

• N(B0) = 72.1 9.4 events• N(B0) = 67.2 9.1 events• ACP = -0.035 0.094 0.022

BB00 K* K*00: CP asymmetry: CP asymmetry

K*0

K*0

-

ws

ws

iiNEWSM

iiNEWSM

eeAAKB

eeAAKB

wsSM

NEW

CP

AA

KBKB

KBKBA

sinsin

22

22


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) < 1.94 x 10-6 90% C.L.• PDG: Br(B0 ) < 3.9 x 10-5 90% C.L. (L3)

Branching ratio measurementcoming soon…B0


FutureFuture

• more sin2 modes in preparation (J/K*, cKs,...)

• Run 2 has started in Feb. 2001 and should be endedin June 2002. Run1 + Run2 100 fb-1

• studies of decay modesfor other unitarity angles and analysis started


Conclusions (I)Conclusions (I)• From Oct. 99 to Nov. 2000, BaBar has recorded

22.7 106 BB pairs and a large sample of hadronic B decays has been fully reconstructed.

• High precision measurements of neutral/charged B lifetimes:

0 = 1.546 0.032stat 0.022syst ps = 1.673 0.032stat

0.022syst ps 0 / = 1.082 0.026stat

0.011syst

• competitive result on mixing parameter md:md = 0.519 ± 0.020 ± 0.016 ps-1

• sin2 was extracted from ~500 CP mode events: sin2 = 0.34 ± 0.20stat ± 0.05syst


Conclusions (II)Conclusions (II)• First evidence of charmonium production in continuum• Precise measurements of exclusive charmonium decays

First observation of B0C1 K*0: Br(B0 c1 K*) = 4.8 1.4 0.9

• First observation of color suppressed mode: Br(B D*D*K) = (0.340.160.11)10-2

• Measurements of charmless 2-body decays: Br(B0 K) =(16.7 1.6 +1.2

-1.7)10–6

Br(B0 ) =(4.1 1.0 0.7)10–6

Br(B+ ) =(5.1+2.0-1.8 0.8)10–6

Br(B+ ) =(10.8 +2.1-1.9

+1.0-1.2 )10–6

• Radiative penguin decay: Br(B0 K*0) = (4.39 0.41 0.27) 10-5

ACP = -0.035 0.094 0.022• More statistics will permit to measure to improve the current

measurements and to access more rare channels!

L.Lista INFN Sezione di Napoli

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