Inclusive Semileptonic B Decays at BABAR

Inclusive Semileptonic B Decays at BABAR

IntroductionThe BABAR DetectorDetermination of |Vcb|Determination of |Vub|Conclusion and Outlook

IntroductionThe BABAR DetectorDetermination of |Vcb|Determination of |Vub|Conclusion and Outlook

19th International Workshop on Weak Interactions and Neutrinos

Thorsten Brandt (TU Dresden)

for the BABAR Collaboration

2 Thorsten Brandt (TU Dresden)

Introduction Semileptonic B decays provide

pure method for determination of |Vcb| and |Vub| theoretical framework : OPE / HQE

Analysis of final states yields additional information : b quark mass „“ nonperturbative QCD parameters

(-) kinetic energy squared of b-quark in B-meson „“ consistency checks of OPE / HQE

Inclusive precision measurements small statistical and systematic errors high sensitivity to theoretical uncertainties


Qualitative Overview

,1shape

)( lXBBr c

|| cbV

)( lXBBr u

uc ,

,e

,eW

...,,,,,, (*)*** DDDDB

K

|Vcb|2, |Vub|2

Rate for Mx < 1.5

|| ubV

Shape

Shap

e

Rate

Inclusive El spectrum

Inclusive Mx spectrum

Semileptonic B decay

2|| cbV

2|| ubV

2|| cbV

HXbq

El[GeV]


Inclusive Spectra & HQE Heavy Quark Expansion relates s.l. decay rate and

|Vcb| :

related to b-quark mass 1 : (-) kinetic energy squared of b-quark in B-meson

2 : chromo-magnetic coupling of b-quark spin to gluon

field

Similar expressions for shapes of Mx and El spectra for different threshold momenta of the lepton first moment of invariant mass-squared of hadronic

system

)1

(02.018.395.087.0165.154.11192

||369.0

)(

322

21

2

2

3

522

BBBB

s

B

sBFcb

c

mO

mmmmmGV

eXB

)1

(02.018.395.087.0165.154.11192

||369.0

)(

322

21

2

2

3

522

BBBB

s

B

sBFcb

c

mO

mmmmmGV

eXB

,...),,( 212

minmin

EEEx fM

l

Combined fit to measurements of Mx2 for different Emin

and to measurement of (BX l)


The BABAR Detector

BBSYee )4( BBSYee )4(


)2,2,5( 4321 nnnn

Problem 1: Two B mesons decaying in the detector which tracks belong to the semileptonically decayed B ?

Use events with fully reconstructed hadronic B decay: look for decay modes

using

Momentum and flavor of both B mesons determined

Identification of S.L. Decays

040321

(*) nKnKnnDB sreco

2,

42 s

EEps

Mrecoreco BBES

2,

42 s

EEps

Mrecoreco BBES

K

recoB

HX

,e

,e

(*)D

Y(4S)K

SLB


4000 fully reconstructed B decays/fb-1

purity 65% if lepton is present

Does the lepton originate from a semileptonic B decay ? exclude s.l. D decays :

Is the XH - system complete, i.e. has no particle been missed ? check missing 4-momentum

Pmiss must be compatible with neutrino hypothesis :

0)( lBb QQSL

0|| missP

tracks alle

iSYmis PPP )4(

5.20 5.22 5.24 5.26 5.28 5.30

mES [GeV/c2]

2200200018001600140012001000800400200

0

Eve

nts

/ (2

.5 M

eV/c

2 )

x 102 All Events

Identification of S.L. B decays

5.20 5.22 5.24 5.26 5.28 5.30

mES [GeV/c2]

12000

10000

8000

6000

4000

2000

0

Eve

nts

/ (2

.5 M

eV/c

2 )

1 lepton, pl > 1 GeV/c


Mx2 Analysis : Event

Selection 1 lepton with p*>0.9 GeV/c Mx

2 determined by 2C kinematic fit energy conservation, p2

miss = 0, mB

1Hreco XlBtot QQQQ

GeVEmiss 5.0 cGeVpmiss /5.0||,

GeVpcE missmiss 5.0||

HX

,e

,e

(*)D

Y(4S)

K

2/350)( cMeVMx

signalbackground

K

(p* >0.9 GeV/c)

(p >0.5 GeV/c E>0.5 GeV) 5.22 5.23 5.24 5.25 5.26 5.27 5.28 5.29

mES[GeV/c2]

225020001750150012501000750500250

0

Eve

nts

/ 1.8

MeV

/c2

high mass final states

Mx2[GeV2/c4]

B

BBABAR


Determination of Mx2

Measured Mx2 differs from true Mx

2

For each interval in Mx2, full detector

simulation delivers Mx2 and Mx

2 calibration curve which is applied to

data event-by-event weak dependence on decay model validated on data with decays function of multiplicity and

Event selection efficiency depends on decay mode

influence on Mx2 determined with MC,

systematic error estimated by variationof individual exclusive decay modes

missmiss pE

)()( 22xx MM highlow

lDB *

0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 pmin[GeV/c]

4.5

4.4

4.3

4.2

4.1

4.0

Mx2

[G

eV2 /

c4 ]~

calibration (D,D*, D**,D(*) mix)

verification withexcl. modes

D

*D

.Resnon

**D

3 4 5 6 7 8 9 10 11 12 Mx

2 [GeV2/c4]

1211109876543

Mx2

[G

eV2 /

c4 ]

~

~


Mx2 - Fits to BABAR

Moments Extract OPE parameters from

fit to Mx2 vs. pl - curve

include correlations based on work of Falk

and Luke

Comparison with CLEO and DELPHI : All hadronic moments consistent

:,)5.0(,0,128.0

2233

21

1

22

fixedFor

GeVGeV iT

2exp1

exp

09.036.0

09.053.0

GeV

GeVMS

MS

0 0.2 0.4 0.6 0.8][GeVMS

-0.1

-0.2

-0.3

-0.4

-0.5

1M

S [G

eV]


Include measurement of inclusive semileptonic branching fraction into the fit SL = (4.37 0.18) x 10-11 MeV

Good agreement with hadronicmoments from CLEO, DELPHI

Moments of lepton spectrum agreement on the 1 level when

using CLEO/DELPHI lepton momentsinstead of BABAR hadron moments

- expect higher precision after inclusion of BABAR measurements -

Combined Fit to Mx2

and SL

3

/1dimexp

2/1dimexp

11

2/1dimexp

1

1050.052.004.110.42||

04.004.006.026.0

/07.006.009.064.4

3

3

3

B

B

B

mBLMcb

mBLMS

mBLMS

b

V

GeV

cGeVm

4.4 4.6 4.8 5.0

44

43

42

41

40

39

38

|Vcb

|[10-3

]

mb1S [GeV/c2]


Measurement of Br(BXu l )

Use Mx spectrum of XH

good b c l rejection large acceptance (50- 80%)

Problems : leading order dependence on

shape function of Mx

low statistics of Breco sample

Additional event selection : lepton with p* > 1 GeV/c veto on K+, K0

s anddecays

m2miss < 0.5 GeV2/c4 , Qtot = 0

lDB *0

2/55.1 cGeVMx


cut momentum lepton through biasfor correction

sample through biasGeV/c1.55Mwithfractionsignalf

efficiencysignal2

xu

:/:/

::

)/()(

)(

)(

ue

SLe

recout

SLt

usel

ut

ul

SLt

SLl

sl

uuselbgdatau

B

N

fNN

eXBBreXBBr

Br(BXu l ) : Signal Extraction

Extract number of signal events by fitting sum of 3 shapes to Mx distribution : signal, b c l background, other sources (<1%,

misidentified leptons, and secondary charm decays)

S / B comparable to excl. analyses : B0 : S/B 3.6 , B+ : S/B 1.2


B Xu l : Results Branching fraction :

Extraction of |Vub| : formula from CKM 2002 workshop , B=(1.608

0.016) ps:

3

2

10)39.026.027.024.2()(

10)36.023.025.006.2()(

)(

theosyststatu

theosyststatu

lXBBr

xlXBBrlXBBr

:)%3.018.087.10()( sysstatlXBBr oftmeasuremenBABAR using

)052.0020.00.1(55.1

002.0

)(00445.0|| 3/1

2/1

bmpertB

uub

lXBBrV

ps

310)26.040.027.028.062.4(|| theosyststatubV

error due to extrapolation and efficiencyerror of transition (BXu l ) |Vub| (Uraltsev, Hoang)


Conclusions & Outlook Precise measurements of and decays :

New model-independent determination of moments of hadronic mass distribution in semileptonic B decays fully consistent with measurements from DELPHI and CLEO

BABAR measurement of moments of lepton energy spectrum in progress measurements for different values of Emin, starting at 0.6

GeV tighter constraints on OPE parameters and |Vcb|

lcb lub

3

3/1

2/1

1

10)26.040.027.028.062.4(||

10)50.052.004.110.42(||

/)07.006.009.064.4(

3

3

theosyststat

BLMdimexp

BLMdimexp

ub

mcb

mS

b

V

V

cGeVm

b

b


Backup Slides


Systematic studies on <Mx

2> Cross-check on data :

sample ofdecays identified by reconstruction of slowpion from

analysis on this sampleyields D* - mass

Consistent measurements inindependent data sets electrons / muons , years, B0 / B+

variation of cut on variation of Breco purity

• add / remove decay channels

eDB *0

sDD 0*

|| missmiss pE


Fit to Moments

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Inclusive Semileptonic B Decays at BABAR

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