Charmless B Decays at B A B AR

11 Sep. 2001, HF9 C. Dallapiccola, Charmless B Decays from BaBar

Charmless B Decays at BABARCharmless B Decays at BABAR

Carlo DallapiccolaUniversity of Massachusetts,

AmherstFor the BaBar Collaboration


• Charmless B Decays bu (CKM-suppressed Tree |Vub/Vcb|2 0.006)

bs,d (Penguins, induced FCNC) Higgs, SUSY particles can contribute to loops additional phases CP violation

• Decay Modes 2Body , K, KK Quasi-2Body 3Body

OverviewOverview

πaφπ,,φKωK,π,η,Kη (*)(*)(')0

0*000 ,,, K

b uu

sd ,

W

W

t

b sd ,

u

u

g


Motivation: CP ViolationMotivation: CP Violation

• Significant amplitudes for Penguins for most modes PT interference possible direct CP violation

“Pure” Penguin K(*), K0 Negligible direct CP violation in SM probe new

physics!

coscos||||2||||

sinsin||||222 TPTP

TP

fBfB

fBfBACP

=weak(strong) P-T phase diff.

•Pbs

•Pbs

)0,0( )0,1(

),(

|| *

*

cbcd

ubud

VV

VV

|| *

*

cbcd

tbtd

VV

VV


Motivation: CP ViolationMotivation: CP Violation

• Indirect CP violation via interference with bu Tree dominated: B0 sin2

Penguins not negligible:

Pure Penguin: B0K0’K0 sin2 Compare with sin2 from charmoniun modesNew physics in Penguin loops

• Measure as many of the charmless BR as possible Factorization tests constraints on from BK extract from B (isospin) Importance of final state interactions

00 BB

TPOACP /12sin

4.0/18.0 TP


• BRs O(10-5) high luminosity B-Factory Run1: Oct. 99 – Oct. 2000 20.7 fb-1 (4S) 22.7 million BB 2.6 fb-1 Off-peak udsc

continuum

• Large bkgd from :

(4S) boosted by =0.56 1.6 < ph < 4.4 GeV/c for Bhh’ dE/dx from tracking devices

provides little K- separation DIRC performance critical

Experimental IssuesExperimental Issues

qq65 1010

BRBB

qq

B background

signal

CMS track momentum


Background SuppressionBackground Suppression

• Topological variables (CMS) Fox-Wolfram moments: R2

Cosine of B thrust axis wrt rest of event: cosT

Cosine of B decay axis wrt beam axis: cosB

Energy flow of tracks/clusters around B thrust axis

• Combine many of these (correlated) quantities into a Fisher Discriminant/Neural Network

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Background SuppressionBackground Suppression

cosT

Bkgd

Signal Bkgd

Signal

cosB

Signal

Bkgd

Fisher

Neural Net

~103 background

rejection factor

~103 background

rejection factor


K- Separation: DIRCK- Separation: DIRC

c

Particle

Quartz bar

Cerenkov light

Active Detector Surface

mp

nc

1cos

DCH DIRC

• The DIRC is able to identify particles via a measurement of the cone angle of their emitted Cherenkov light in quartz

• Want good /K separation for wide momentum range (up to 4 GeV)


K- Separation: DIRCK- Separation: DIRC

• DIRC c resolution and K- separation measured in data D*+ D0+ (K-+)+ decays

Proton rejection cut

Track momentum (GeV/c)

Che

renk

ov a

n gl e

>8

~2.5


Exclusive B ReconstructionExclusive B Reconstruction

• B mesons ~ rest (325 MeV/c)

• Bhh’ decays(mES) 2.5 MeV/c2

(E) 25 MeV

BBS )4(

2*2beamES

*BpEm

*beam

* EEE B

Kinematic separation of KK, K, decays in E

MC

Fully reco B


B3Body: +-0B3Body: +-0

• Cut-based: cosT, Fisher (F), cosH, mES, E

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)()( 0202 mvsm )()( 0202 mvsm

• Cuts optimized for each Dalitz region

• signal in

0B


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B3Body: B3Body:

• Asymmetry also measured:

5 signif

02.018.004.0

)()(

)()(

A


B3Body: K*0+B3Body: K*0+

• Similar to analysis cut-based• K*0K+-

BR(B+K*0+)=(15.5 3.4 1.5) 10-6

Significance = 5.3


B(Quasi-)2BodyB(Quasi-)2Body

• Use unbinned maximum likelihood (ML) fits Retain high efficiency with multi-dimensional signal-

background discrimination Cut-based analyses as cross checks

P = product of PDFs for uncorrelated observables = {mES, E, F, c, mres, H,…}

)()(

! 1

ibkgj

bkgjji

sigj

sigjji

iNi

n

xPnxPnL

LN

eL

j

ix

ix


BQuasi-2Body: (/)K(*)BQuasi-2Body: (/)K(*)

• Tree is CKM suppressed b s Penguin

Signals in K* and ’K

Signals in K* and ’K


BQuasi-2Body: (/)K(*)BQuasi-2Body: (/)K(*)

• Signal also in B++ b u Tree dominates0


Inclusive B’XsInclusive B’Xs

• High rate for B’Xs first observed by CLEO

For 2.0 < p’ < 2.7 GeV/c

QCD anomaly interpretation

(g-g-’ coupling)

40.05.1 10)3.16.12.6(

BR

• Reconstruct Xs in 8 modes:

)(

30)(00

0

nK

nnKB

S

40.05.0

7.00.1 10)6.08.6(

BR


BQuasi-2Body: K(*)BQuasi-2Body: K(*)

• ~Pure Penguin K0 CP eigenstate (sin2)


BQuasi-2Body: a0BQuasi-2Body: a0

• ML fit with NN, m(), mES, E

60.35.2

60

0

10)1.12.6(

%90105.11))((

CLaBBR

3.7 statistical significance

Cut-and-count cross check


B2Body: /K/KKB2Body: /K/KK

• ML fits to signals in following topologies (simultaneous fits to contributions with charged K and ):

00

00

0

0

SS

S

S

KK

K

Kh

h

hh

All Charged Modes

All Charged Modes



• Bh+h- data analyzed with 50% more data from Run2 No updated BRs, but

B0K+- direct CP updated

30.4 fb-1



h+0h+0

K00K00

K0+K0+


B(Quasi-)2Body: CP AsymmetriesB(Quasi-)2Body: CP Asymmetries

02.008.007.0 04.018.000.0 03.018.021.0 02.011.011.0

03.001.0 29.031.0

06.043.0 36.030.0

03.020.005.0

03.027.000.0

20.7 fb-

1

30.4 fb-

1

• No evidence of direct CP

Excluded 90% CL


SummarySummary

• Search for 28 charmless hadronic B decay modes

Signals observed in 17 of them Approaching BR sensitivities of O(10-6)• No evidence yet for direct CP violation

Sensitivity of ~10% for some modes

• Important modes: Constraining Constraining/Measuring Measuring K0

• Still taking data Results here based on ~23 million pairs ~115 million pairs by end of Run2 (Summer 2002)

BBBB

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Charmless B Decays at B A B AR