New results from B A B AR, Marie-Hélène Schune, BNL, May 20th 20021 New results from B A B AR Marie-Hélène Schune Laboratoire de l’Accélérateur Linéaire

New results from BABAR, Marie-Hélène Schune, BNL, May 20th 2002 1

New results from BABAR

Marie-Hélène SchuneLaboratoire de l’Accélérateur LinéaireOrsay, France

All numbers are preliminary

Brookhaven National LaboratoryParticle Physics Seminar

May 20, 2002


New results from BABAR

• I will not talk about – sin2 in charmonium modes :

1. BABAR and PEPII2. Charmless B decays :

– B0, K or KK – B000

3. The “B recoil” physics :– semileptonic branching fractions of B+ and B0

– D meson production in B decays

sin20.750.09 0.04

56 fb-1

Winter 2002 conferences


– CKM matrix has 4 real parameters (one phase included)

– 2 are well known :• =|Vus|=sin(Cabbibo)=0.22050.0018

• A =|Vcb|/2 =0.83 0.06

– unitarity of the CKM matrix leads to constraints that can be tested:

2 3

2 2 4

3 2

1 / 2

1 / 2

1 1

ud us ub

cd cs cb

td ts tb

V V V A i

V V V V A

V V V A i A

CKM matrix for 3 generations

Bd ,, …

Bd J/Ks, D*+D*-,…B D*, DK, K

B , , l, l,…

BdBd, Bd

B D(*)l,D(*),…

* * * 0ud ub cd cb td tbV V V V V V

Unitarity Triangle


DIRC (PID))

1.5T solenoid CsI(Tl) EMC

Instrumented Flux Return

Silicon Vertex Tracker

Drift Chamber

e+

(3.1GeV)

e-

(9GeV)• SVT: 97% efficiency, 15m z resol. (inner layers, perpendicular tracks)• Tracking : pT)/pT = 0.13% PT 0.45%• DIRC : K- separation >3 for P<3.5GeV/c• EMC: E/E = 1.33% E-1/4 2.1%

The BABAR detector



PEP-II asymmetric B Factory9GeV e- on 3.1GeV e+ :s~10.58 GeV

• for B0 : coherent neutral B pair production and decay (p-wave)

• boost of (4S) in lab frame : =0.55

-e e (4S) BB


Running at the (4S)

Off On

)MeV(ME )S4(CM

PEP-II

BABAR

28.0hadr

bb


• May 2nd : – PEPII delivered : 87 fb-1

– BABAR recorded : 83 fb-1 (including 9 fb-1 off peak )

• results for 55 fb-1

B factory performances

daily integrated luminosity


2 - Charmless B decaysStudy of penguins diagrams Possible direct CP violation

• B0, K or KK – Branching fractions (eff , )

– CP violations measurements (eff , )

• B000 (eff )

(,)


B0 and CP violation (1)

/

( ) 1 sin cos4

t

d d

ef t S m t C m t

BF(B0) << BF(B0K) penguins contributions may be large

Hadronic Penguin Amplitude (P)

W

tb d,s

u

u

g

b u,ccu ,

d,s

W

Tree amplitude (T)

Tree only : =fe2i

C=0 S=sin(2)

Tree+Peng.

C 0 S=sin(2eff)

2

2 2

12 m

1 1

q A

p A

S C

mixing e-2i


B0 and CP violation (2)

/

( ) 1 sin cos4

t

d d

ef t S m t C m t

0 0

0 0

sin cosB Bd d

B B

N NA S m t C m t

N N

00tag BB 00

tag BB

perfect flavour tagging & time resolution

00tag BB 00

tag BB

realistic mis-tagging & finite time resolution

S=0.7and C=0.

f+ : B0 tag


• Main variables :– |cosS| : angle between the B0

sphericity axis and the sphericity axis of the rest of the event

– F : Fisher discriminant based on “energy flow cones” (CLEO)

B0, K or KK kinematics

sθ

sθ

“Jets”

Candidate

Axis of “Rest Event”

-e e qq

Axis of “Rest Event”

Candidate

0- 0e e B B |cosS|

Candidate


Signal MC ~2.6 MeV

background

B0, K or KK : mES and E• Energy substituted mass :

– dominated by the beam energy knowledge

• E : assume mass

– dominated by the tracking resolution(E)~26 MeV

2

*2/ 2ES Bm s p

* / 2BE E s

KKK

~325 MeV

background

mES

45 MeV


B0, K or KK : the PID (1)The DIRC

• Measure Angle of Cherenkov Cone in quartz

– Transmitted by internal reflection– Detected by PMTs

2 2

1cos and c

pn p m

c

Particle

Quartz bar

Cherenkov light

Active Detector Surface


DIRC PMT +light catchers

DIRC stand-off box, magnetic shielding and electronic crates


B0, K or KK : the PID (2)• DIRC performances measured on data using D*D0

and D0 K

(c) 2.2 mrad K/ separation

2.5

p range of 2-body B decays at BABAR


0 0

Kπ 0 0

Kπ 2 2

Γ(B K π ) Γ(B K π )A

Γ(B K π ) Γ(B K π )

2 sin sinA

2 cos cos

P T

P T P T

B0, K or KK : analysis strategyStart with a B0h+h- (no PID)

5.2 5.24 5.28

mES

~17600 events for ~56 fb-1

unbinned max L with

E, mES, F, 1c, 2c

measure N NK NKK and

add t and tagging information (as for sin2), fix the yields extract S and C


B0 B0K

B0, K or KK :branching fractions results

01.006.005.0

4.07.04.5

8.01.18.17

CL) (90% 1.1

1615124

247.402

Mode Yield Branching Fraction (10-6)

KAsymmetry (AK

B0+-

B0K-+

B0 K+K- 876.0

Likelihood projections : remove one 1 variable from fit ; cut on L proba

mES E mES E

small cross-feed

small cross-feed

~83 B0 ~356 B0K


B0, K or KK : BF comparison

CLEO 9 fb-1 BABAR 56 fb-1 BELLE 31fb-1

BF(B0+-)(10-6) 4.31.60.5 5.40.70.4 5.11.10.4

BF(B0K-+)(10-6) 17.22.51.2 17.81.10.8 21.81.81.5

BF(B0K-K+)(10-6) <1.9 at 90%CL <1.1 at 90%CL <0.5 at 90%CL

AK-0.040.16 -0.060.050.01 -0.060.080.01

BF(B0) << BF(B0K)


B0, K or KK : CP analyses t

• Time information t :– resolution dominated by Btag vtx ((z) ~ 180 m)

– extracted from data Breco sample (D(*),D(*),D(*)a1…)

– Background shape : side bandsSimilar to sin(2) analyses


NN output

Not U

sed

Prob(B0)

B Flavour tagging methods

For electrons, muons and kaons use the charge correlation

b c

d d

l-

B0 D, D*

W-

0

0

l

l

B

B

Lepton Tag

b

d

B0

W- W+c s

K*0

d

0

0

0

0

kaons

kaons

Q

Q

B

B

Kaon Tag

Each category is characterized by the probability of giving the wrong answer (mistag fraction w)

Multivariate analysis exploiting the other kinematic information of the event, e.g., Momentum spectrum of the charged particles Information from non-identified leptons and kaons Soft from D* decay

Neural Network

Hierarchical, mutually exclusive, tagging categories


B0, K or KK : CP analyses tagging• Split the events into 4 tagging categories :

– leptons– kaons– NT1– NT2

• Performances obtainedon data (Breco sample)

Similar to sin(2) analyses

NN type tagging

leptons

kaons

NT1 NT2

mES


B0, K or KK : CP analyses validation• Validation : measure B on /K sample :

• Validation : measure md

B=1.66 0.09 ps

md=0.517 0.062 ps-1

cosmix umix

mix dmix umix

N NA t m t

N N

/

/

1 cos4

1 cos4

mix

un

t

t

dmi

d

x

eP t m t

eP t m t

Select the Kevents and plot Amix


B0, K or KK : CP analyses resultsS =-0.010.370.07 S[-0.66,+0.62] at 90 % CL

C =-0.020.290.07 C[-0.54,+0.48] at 90 % CL

~27 B0~9 Background

~25 B0~9 Background

Select the B0 events

Plot the asymmetry between B0 tag and B0tag events

0 0

0 0

sin cos

B B

B B

d d

N NA

N N

S m t C m t


BBNS: QCD FACTORISATION APPROACH:M. Beneke, G. Buchalla, M. Neubert and C.T. Sachrajda Nucl.Phys.B606 (2001) 245

(,) constraints from S and C

CKM Fitter

H. Höcker, H. Lacker, S. Laplace

and F. Le Diberder

Eur. Phys. J. C21 225-259 (2001)

http://ckmfitter.in2p3.fr/


B0, K or KK : CP comparisonsBelle (K Trabelsi Moriond):

-C (BABAR)

2(SC

A


Search for B000

• BF(B000) : – measured isospin analysis to get from B0+-

(M. Gronau, D. London Phys Rev Lett. 65 3381-3384 (1990))

– upper bound still a useful constraint: (Y. Grossman, H. Quinn Phys Rev D 58 017504 (1998))

• Experimentally challenging :– low BF expected (th. predictions : 10-7 - few 10-6)– purely neutral final state

• Recent results :

0 0 0

2

0

B upper boundsin

BF Beff

Yield limit (10-6) (90% CL)

CLEO (9 fb-1) 6.2+4.8-3.7 5.7

BELLE (30 fb-1) 126 5.6


• Main variables :– |cosS| : angle between the B0 sphericity axis and the sphericity

axis of the rest of the event– F : Fisher discriminant based on the “energy flow cones”

– mEC : energy constrained mass

– E = E*B –s/2 in the CMS

Search for B000 : analysis (1)

“Jets”

Candidate

Axis of “Rest Event” sθ

sθ

-e e qq 0- 0 0 0e e B B F

Candidate


Search for B000 : analysis (2)• The B 0 background :

– event shape similar to the signal one– mEC only slightly wider (small missing)

– E is the only discriminating variable– in the fit : fix BF(B 0)=2.410-5 (from CLEO upper limit)

E (GeV)

E (GeV)-.4 -.2 0 .2 .4 -.4 -.2 0 .2 .4

B 0 B000


• Unbinned maximum L fit using F PDF and (mEC , E ) PDF

• Compare with an optimized cut and count analysis :

• Fit yield :

Search for B000 : results

BF(B000) < 3.4 10-6 at 90 % CL

7.76.19.8 8.7 Main systematics :

•neutral efficiency•continuum mEC param.•F param.•B 0 yield

54 fb-1


3 - The “B recoil” physics

generic B decay B type knownshould allow (in principle !) to measure all B BFWill show : leptonic studies

D0 and D production


The “B recoil” physics• B factories : the world’s largest sample of reconstructed

B mesons 56 fb-1

B0 sample

Nsignal=13743125

B+ sample

Nsignal=12909120

0( )B D π 0

1( )B D π /ρ /a

Reconstruct the Cabibbo-favored hadronic decays :


Inclusive semileptonic B decays• Inclusive rate is large

– Sides of the unitarity triangle |Vcb| and |Vub|

– BXce is large

– BXueis an experimental challenge

(0,0)

()

*

*ud ub

cd cb

V VV V

*

*td tb

cd cb

V VV V

(1,0)


• Compare b+/b0 with (B+)/(B0) :

• Extract the prompt and cascade lepton spectrum from the charge correlation with the Breco :

– B-Xce-

– B+Xce+

– B0 : correct for mixing

CLEO results (2.4 fb-1) using B0 tagged sample and (4S) l :

– b0 = (10.78 0.600.69)%

– b+ = (10.25 0.570.65)%

– b+/b0 =

Inclusive semileptonic B decays

0.1170.0800.950 0.091

0

0

0 00

//

sl tot tot B

sl tot tot B

bb


Electron identification• Variables :

– E/p– Shower shapes– DCH and DIRC

• Performances measured on data:

90%

•Backgrounds :

conversions

0 dalitz decays

-J/ decays10-3

p (GeV)


Background subtracted electrons spectraRight sign Wrong sign

B

N right sign= N+p

B0

Nright sign=N0p(1-d)+N0

cd

Nwrong sign=N0pd+N0

c(1-d)

results on 21 fb-1


b+/b0=.950 .080 .091b+/b0=.99 .10 .03

b0 and b+ results

• BF results : ratio :

B+ B0


• Inclusive branching fractions of B0 and B+ to charmed hadrons

– Enters in the nc (= mean charm per B decay ) computation

• For each B specie two measurements are performed :• The absolute BF : BF(BDX) with D = D0 or D+

– “large statistics”– Need (D) from MC

• The wrong D ratio : – Wrong D sample statistically limited – Need to correct for mixing for the B0

– More MC independant

D production in B decays

BF B DXD

BF B DX BF B DXw

DDDsc

,…

bc

sDDDs

c,…

WRONG

RIGHTq

c

B0 or B-

( )


D production in B decays reconstruction Hadronic :

– B0 D*D*D*a1

Semileptonic: B0 Dl

fit to cosB-D*l variable

mES cosB-D*l

•D reconstruction : D0 Kand D K

50 fb-1


BF(BDX) • Fit N(D) and correct for Brec background BF(BDX)

( )

( )

Brec : B0 D*l

M(K)

M(K) M(K)

M(K)

Brec : B0 D*D*D*a1

BF(B0D0X)(%)

Semilep. 57.1 3.3 4.6

Hadronic 59.3 5.9 3.9

Combined 57.9 2.9 2.1(*) 3.5(**)

( )

BF(B0DX)(%)

Semilep. 35.7 2.8 3.9

Hadronic 35.3 4.3 3.8

Combined 35.6 2.3 1.1(*) 3.6(**)

(*) Correlated syst.(**) Uncorrelated syst.


w(D) for neutral B mesons• Correlate the D and the B flavours :

– For B0 : should correct for mixing

• done on an optimized time interval (|t|<2.5 ps) reduced statistical uncertainty, md dependance

obs =Mix

Mix+Unmix= d + w (1 2 d)

Unmix

Mix

Brec : B0 D*l Brec : B0 D*D*D*a1

M(K)

w( B0 D X) (%)

Semilept. 7.3 3.7 1.9

Hadronic 8.9 7.1 1.8

Combined 7.7 3.3 1.4 0.8

w( B0 D 0X ) (%)

Semilept. 15.9 3.5 2.4

Hadronic 9.6 4.7 1.1

Combined 13.1 2.8 1.5 0.6


• Results suggest B0 spectator quark effect negligible in wrong D production

• Results consistent with world data (“B admixture”)

• In the future : – Add the B sample – 100 fb-1

– start to look for Ds and c (looser Breco selection ?)

BF( B0 D0X ) = ( 50.3 3.0 3.7 ) %BF( B0 D0X ) = ( 7.6 1.7 1.1 ) %BF( B0 D+ X) = ( 32.8 2.5 3.5 ) %BF( B0 D- X) = ( 2.7 1.2 0.6 ) %

D production in B decays

Better understanding of the overall picture of the B decays

Compare BF( B0 D0 + D+ X) = (83.1 6.4) % withworld data: BF( Badmixt

D0 + D+ X) = (78.5 3.4) %

30 or 51 fb-1


Summary• A true factory of B mesons :

– BF(B0 +-) = (5.40.70.4) 10-6

– BF(B0 K+-) = (17.81.10.8) 10-6

Unfortunately not enough to get B000

– BF(B000) < 3.4 10-6 at 90 % CL

• CP violation results :– S =-0.010.370.07

– C =-0.020.290.07

• “B recoil” physics is starting :– Semi leptonic measurements– D mesons production in B

decays

BF( B0 D0X ) = ( 50.3 3.0 3.7 ) %BF( B0 D0X ) = ( 7.6 1.7 1.1 ) %BF( B0 D+ X) = ( 32.8 2.5 3.5 ) %BF( B0 D- X) = ( 2.7 1.2 0.6 ) %

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New results from B A B AR, Marie-Hélène Schune, BNL, May 20th 20021 New results from B A B AR Marie-Hélène Schune Laboratoire de l’Accélérateur Linéaire