cb (ub) w+ - university of pennsylvania · av erage for b! d ` f rom lep j v cb j w orking group up...

$: cb (ub) W+ - University of Pennsylvania · Av erage for B! D ` F rom LEP j V cb j w orking group up dated for PDG02 Adjusted to common set of input parameters D branc hing fractions$
K. M. Ecklund (Cornell) Semileptonic B Decay { jVubj and jVcbj

Semileptonic B decays { jVubj and jVcbj

b

e+

ν

c (u)

dd

W+

c (u)X

Vcb (ub)0B

Karl Ecklund, Cornell University

May 18, 2002

8 May 2002 FPCP02 University of Pennsylvania 1

K.M.Ecklund(Cornell)

SemileptonicB

Decay{jVub jandjVcb j

Outline

�Introduction:CKM

fromsemileptonicBdecays

�jVcb j

{Exclusivedecays:B!D(�)`�

{Inclusivedecays:B!Xc `�

�jVub j

{Exclusivedecays:B!�`�;�`�

{Inclusivedecays:B!Xu`�

�SummaryandOutlook

8May2002

FPCP02UniversityofPennsylvania

2


CKM Measurements in Semileptonic B Decays

b

e+

ν

c (u)

dd

W+

c (u)X

Vcb (ub)0B

�(b! x`�) =G2F

m5b

192�3jVxbj2

Rates give CKM2

��

��

–Complication!

QCD Corrections needed

to extract weak decay physics

perturbative corrections and

non-perturbative QCD Corrections: from HQET, Lattice QCD

Use many techniques and compare results to gain con�dence in QCD corr.



jVcbj from �B ! D(�)`��

Extracting jVcbj from exclusive decays:

The decay rate is given by

d�dw=

G2F

48�3jVcbj2[F(w)]2K(w)

w = vB � vD(�) =m

2B

+m2D

(�)�q2

2mBm

D

(�)

I

b

c

c

I

q

q

qII

II

I w = 1

w > 1

� K(w) contains kinematic factors and is known

� F(w) is the form factor describing B ! D(�) transition

� HQET relations simplify the form factor

� HQS normalizes at zero recoil (w = 1): As MQ !1, F(1)! 1

Plan: Measure d�=dw and Extrapolate to w = 1 to extract F(1)jVcbj.



SemileptonicB


B!

D(�)Form

Factor-QCD

complications

�Mustknowformfactorshapetoextrapolate

�MustknowF(1)toextractjVcb j

ThemostgeneralLorentz-invariantformfactorissimpli�edby

�Masslessleptons

{ForB!D`�onlyvectorcurrentoneFF:F1

{ForB!D�`�threeFFs:A1 ,A2 ,Vbut...

�HeavyQuarkSymmetry

{MQ

!1:oneformfactor,thefamousIsgur-WiseFunction

{FormFactorRatiosR1andR2approximatelyconstantinw

�QCDdispersionrelationsconstraintheshape(Boydetal.)

{ParameterizationofFF:Caprinietal.NPB530(1998)153

{Includescurvaturebutoneshapeparameter:�2,slopeatw=1

8May2002


5


CLEO �B ! D�`�� hep-ex/0203032

Fit

Fit

300

200

100

0160

120

80

40

0

Can

did

ates

/ 0.

05

Data

Data

Fit

0.05

00.01

0.020.03

0.04

1.0 1.51.41.31.21.1w

3070901-028

D*0

D*0

D*+

V

cbII

II F (

w)

D*+

(3.1 fb�1 3.3 M B �B)

Reconstruct D�+`� and D�0`�

Given yields in 10 w bins

Fit using Caprini form factor

Parameters:

� F(1)jVcbj (intercept)

� �2 (slope)

F(1)jVcbj = (43:1� 1:3� 1:8)� 10�3

�2 = 1:61� 0:09� 0:21

Theory: F(1) = 0:91� 0:04

jVcbj = (47:4�1:4�2:0�2:1)�10�3

7% precision

Systematics! eÆciency, bkgds, BFs



BELLE �B ! D�+e�� PLB 526 (2002) 2580.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0.05

1 1.1 1.2 1.3 1.4 1.5

Dispersion relation

Linear form factor

● Data

y

|Vcb

|F(y

)

(10 fb�1 11 M B �B)

Similar to CLEO and

LEP analyses

Uses only electrons

Extrapolation procedure gives correlation for �2 and F(1)jVcbj



SemileptonicB


AverageforB!

D�`�

FromLEPjVcb jworkinggroupupdatedforPDG02

Adjustedtocommonsetofinputparameters

�D

branchingfractionsandBlifetimes

�Form-factorratiosR1andR2

�B!D�X`�backgroundparameters

FitsforF(1)jVcb jand�2accountingforcorrelationsbetweenexperimental

inputs,systematicsandstatisticalcorrelationbetweenF(1)jVcb j�2

8May2002


8


Results of Average I

25

27.5

30

32.5

35

37.5

40

42.5

45

47.5

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2ρ2

F(1

)|Vcb

|/10-3

ALEPH

DELPHI (Prel.)

OPAL

CLEO

Belle

average

Note correlations in F(1)jVcbj

and �2

5% C.L. from combined �t

N.B. CLEO

� Includes D�0

� Fits data simultaneously

for D�X`� background

Others share D�X`�

estimate & model

Ellipses are ��2 = 1 for each measurement (stat+syst)



Results of Average II

30 32 34 36 38 40 42 44 46

F(1)Vcb (10-3)

World average (prel)Vcb Working Group

38.2±1.1

CLEO(prel.) 43.3±1.3±1.8

BELLE 36.0±1.9±1.8

OPAL 38.2±1.0±1.7

DELPHI(prel) 35.7±2.4±1.8

DELPHI 36.1±1.4±2.5

ALEPH 33.8±2.1±1.6

F(1)jVcbj =

(38:2�1:1)�10�3

With F(1) = 0:91� 0:04 jVcbj = (42:2� 1:1exp � 1:9thr)� 10�3



SemileptonicB


CommentsaboutAverage

�Needcommontreatmentofinputparametersandsystematicerrors

�Essentialtousesameformfactorparameterization

�C(F(1)jVcb j;�2)onsystematicerrorsneeded

ImportantIssuesForFuture

�BackgroundfromB!D�X`�-inputfromnewdata

�FormFactorRatiosR1andR2poorlyknown-canbemeasured

�E�ectofEW

radiativecorrectionsonextrapolationandeÆciency

�F(1)theoryuncertaintycurrently�5%

shouldbereducedwithunquenchedLatticeresults

8May2002


11


SemileptonicB


ChoosingExclusiveFinalStates

�D�`�haslargerratethanD`�

�largerbackgroundinD`�(fromD�`�!)

�V�AkinematicsfavorsD�inextrapolationtoloww

{KD

(w)=(MB

+MD

)2M3D( pw2�1)3

{KD

�(w)/p

w2�1

�Luke'sTheorem:ForF(1),HQS-breakingcorrections

O(1=M2Q)forD�`�andatO(1=MQ

)forD`�

Bottomline:MostinformationfromB!D�`�,butB!D`�canhelp

intheendwithFFparameterdeterminations.

ALEPH,BELLEandCLEOhaveB!D`�measurements:

�LessprecisethanB!D�`�

�ConsistentdeterminationofjVcb j=(41:3�4:0exp �2:9thr )�10�3

8May2002


12


SemileptonicB


Inclusiveb!

c`�

Ratherthanfocussingononehadronic�nalstatewherecorrectionsmay

becalculatedreliably,

Sumoverallstatesandcomparetoquark-levelcalculation

Xi

�(B!X(i)

c

`�)=�(b!c`�)

Reliesonassumptionofquark-hadronduality

Hardtoquantify;mustbetested!

8May2002


13


SemileptonicB


TheoreticalToolsforInclusiveb!

c`�

HeavyQuarkExpansioninpowersof1=MB

and�s

OperatorProductExpansion-introduceparametersasmatrixelements

ofnonperturbativeoperators:

Atorder1=M:

��-�MB

�mb

energyoflightdegreesoffreedom

Atorder1=M2:

�1-kineticenergyofbquarkinBmeson

�2-hyper�neinteractionofbspinwithlightd.o.f.

Atorder1=M3:

�;T-sixmoreparameterswithless-intuitiveinterpretations

andsoon:::

8May2002


14


SemileptonicB


UseHQE/OPEtoolstopredictrate

�

=

G2F jV

cb j 2M5B

192�3

"G0+

1MB G1 (��)+

1M2B G2 (��;�1 ;�2 )

+

1M3B G3 (��;�1 ;�2 j�1 ;�2 ;T1 ;T2 ;T3 ;T4 )+O 1

M4B !#

andmomentsofdecayspectrainB!Xc `�:

hE` i, E2` �, M2X �

[Falk,Luke,Savage,Gremm,Kapustin]

andB!Xs :hE i, DE2 E

[Bauer,Z.Ligetietal.]

Example:

hE i=

M

B2

[1�:385�s

�

�:620�0 (�s

�

)2��

M

B

(1�:954�s

�

�1:175�0 (�s

�

)2)

�13�1�33�2

12M

3B

�T1+3T2+T3+3T4

4M

3B

�

�2C2

9M

B

M

2DC7

+O(1=M4B)]

8May2002


15


SemileptonicB


RoadmapforInclusivejVcb j

Milestones:

�Theory

{Expressionsfor�andmoments

�Experiment

{InclusivebranchingfractionB(B!X`�)

{Lifetimes

{Moments:hE iinb!s , M2X �inB!Xc `�

RecentimprovementsonjVcb juseexperimentalmeasurementsoftheory

parameterstoboundHQETparameters.

Otherimprovementscomefromnewbranchingfractionandlifetime

measurements.

8May2002


16


Inclusive Semileptonic Branching Fraction

Analyses by CLEO, BABAR, BELLE (ARGUS)

0.15

0.10

0.05

00 1 2 3

pe (GeV / c)

dB

/ d

p (

0.1

GeV

/ c)

-1

0970995-001

Use high p lepton to tag B

Measure second lepton

Separate primary and secondary

using charge and

angular correlations

CLEO PRL76 (1996)1570 (2 fb�1) B(B ! Xe�) = (10:49� 0:17� 0:43)%

BELLE CONF-0123 (5 fb�1) B(B ! Xe�) = (10:86� 0:14� 0:47)%

BABAR PRELIMINARY (5 fb�1) B(B ! Xe�) = (10:82� 0:21� 0:38)%

Compare to

LEP Avg Working Group B(b! X`�) = (10:59� 0:09� 0:15� 0:26)%



B ! Xs : E Moments1.5 2.5 3.5 4.5

0

40

E (GeV)

Wei

ghts

/ 10

0 M

eV

Data

Spectator Modelmb = 4690 MeV/c 2

pF = 410 MeV/c

CLEO b! s spectrum

PRL 87, 251807 (2001) hE i � mb=2

Broadened by

� Fermi motion

� gluon bremsstrahlung

� B boost in lab

Use �rst moment to determine ��

�� = 0:35� 0:08� 0:10 GeV

Theory: Bauer PRD57, 5611 (1998)

Ligeti et al., PRD60, 034019 (1999)

hE i = 2:346 � 0:032 � 0:011 GeV

h(E � hE i)2i = 0:0231� 0:0066� 0:0022 GeV2



B ! Xc`�: M2

X Moments

b

e+

ν

c (u)

dd

W+

c (u)X

Vcb (ub)0B

CLEO PRL 88, 251808 (2001)

Require E` > 1:5 GeV

(P� ; E�) from hermetic detector

M2X = M2B +M2`� � 2EBE`� + 2jpBjjp`�j cos �`�;B

� gM2X

= M2B +M2`� � 2EBE`�

0

500

1500

2000

-4 -2 0 2 4 6 8 10

~ 2MX (GeV

2)

Evt

s/.5

GeV

2

FitD l νD* l νXH l ν

CLEO DATA

hM2X �MD

2i = 0:251� 0:023� 0:062 GeV2

h(M2X �MD

2)2i = 0:639� 0:056� 0:178 GeV4

Spin-average D mass:

MD = (MD + 3MD�)=4



Determination of �� and �1

0.1

0

0.1

0.60.40.2 0.80.5

0.4

0.3

0.2

1.00

ExperimentalTotal

II

II

I

I

< E >

1

I

< MX M

D >

2

I2

1850701-004

�� = 0:35 � 0:07 � 0:10 GeV

�1 = �0:238� 0:071� 0:078 GeV2

Warning: scheme dependence

MS to order 1=M3, �0�2

s

Using

B(B ! Xc`�) = (10:39� 0:46)%

(CLEO B ! Xu`� removed)

�B (PDG2000)

gives

jVcbj = (40:4�0:5�0:9�0:8)�10�3

(M) (�) (T)

3.2% determination of Vcb

implicit q-H duality assumption

Work in progress on E` moments

Consistency?

Stay tuned Summer results expected

from many experiments



Experimental Challenges in b! u`�

From Leibovich hep-ph/0011181

dΓ(b→c)/dEe

10 dΓ(b→u)/dEe

Ee (GeV)

dΓ/d

E e

∆E

0 1 2

Large b! c`� backgrounds

� Signal is 1% of background!

� Suppress using kinematics

Approaches:

� Exclusive

+ Constraints from full recon

� Inclusive

+ Kinematic cuts

{ E` >� 2:4 GeV

{ MX < MD

{ q2 >� 12 GeV2

Both approaches currently su�er

from large uncertainties

� Exc. Unknown form factors

� Inc. E�ect of kinematic cuts



SemileptonicB


ExclusiveB!

�`�andB!

�`�

Powerfulkinematicconstraintsforfullreconstruction(�E;MB

)

�reconstructionusinghermticityofdetector:

�Emiss=2Ebeam

� PiEi

�~pmiss=� Pi~pi

EvaluateBusingformfactorsandextractjVub jfrom

�=

B�B

= u jVub j 2

Formfactors(and )from

�Lattice-e.g.UKQCD

�QuarkModels-e.g.ISGW2,WSB

�LightConeSumRules-e.g.BallandBraun

�HQS-e.g.LigetiandWisefromD!K�`�

8May2002


22


CLEO PRL77, 5000(1996) First Observation �B ! �`�� and �B ! �`��

0

5

10

15

20

25

30

35

5.15 5.2 5.25 5.3

b→cb→ulν feeddownρ→π feed acrossπ→π feed acrossπ±lν, π0lν

Mcand (GeV)

<Eve

nts>

/ 7.

5 M

eV

0

10

20

30

40

50

5.15 5.2 5.25 5.3

b→cb→ulν feeddownπ→ρ feed acrossρ→ρ feed acrossρ±lν, ρ0lν, ωlν

Mcand (GeV)

<Eve

nts>

/ 7.

5 M

eV (2.66 fb�1)

E` > 1:5 GeV

S=N � 2

Isospin constraint

� �� = 2��0

� �� = 2��0

B(B0 ! ��`+�) = (1:8� 0:4� 0:3� 0:2)� 10�4

B(B0 ! ��`+�) = (2:5� 0:4+0:5�0:7 � 0:5)� 10�4

Evaluate jVubj using �ve form factors



BELLE-CONF-0124 (2001) �B ! �`��

GeV/c 2

GeV/c 2

(21.3 fb�1)

Belle � reconstruction

Emiss = 2Ebeam �P

iEi

~pmiss = �Pi~pi

E� = j~Pmissj and ~p� = ~pmiss

Cut j�Ej < 0:3 GeV

Fit Mbc

Preliminary

B(B0 ! ��`+�) = (1:28� 0:20� 0:26)� 10�4 ISGW2 +WSB



SemileptonicB


UpdatedatMoriond02(H.Ishino):29.2fb�1

2d-�tto�Eandp`

Usesmorerecentmodelsforformfactors

B(B0!��`+�)

=

(1:89�0:15�0:30)�10�4

LCSR

B(B0!��`+�)

=

(1:92�0:16�0:30)�10�4

UKQCD

8May2002


25


CLEO PRD61, 052001 (2000) �B ! �`��

HILEP ρ modes with M(ππ) cut

∆E (GeV)

0

20

40

-2 -1 0 1 2

HILEP ρ modes with ∆E cut

M(ππ) (GeV/c2)

0

25

50

0.5 1 1.5 2

Looser cuts than 1996; 3.1 fb�1

E` > 1:7 GeV; Most sensitivity for E` > 2:3 GeV

B(B0 ! ��`+�) = (2:69� 0:41+0:35�0:40 � 0:50)� 10�4

Statistically independent of 1996 analysis



SemileptonicB


BABARPRELIMINARY

�B!�e��-B.SerfasatCERNCKM

Workshop

Uses20.2fb�1;VerysimilartoCLEO's�B!�`��

B(B0!��e+�)=(3:26�0:65+0:63

�0:65 �0:44)�10�4

8May2002


27


SemileptonicB


ExclusivejVub jSummary

B(B0!��`+�)�10�4

B(B0!��`+�)�10�4

CLEO

1:8�0:4�0:3�0:2

2:5�0:4+0:5

�0:7 �0:5

2:69�0:41+0:35

�0:40 �0:5

Belle

1:28�0:20�0:26�?:??

BaBar

3:26�0:65+0:63

�0:65 �0:44

CLEOCombined:jV

ub j=(3:25�0:14+0:21

�0:29 �0:55)�10�3

�Limitedbyknowledgeofformfactors

�Latticecalculationscanhelp

�Updatescomingfromallexperiments

8May2002


28


SemileptonicB


Inclusive

�B!

Xu `��

ExtractjVub jfrommeasuredbranchingfractionusingOPE

jVub j=0:00445 �B(B!Xu`�)

0:002

1:55ps

�B

�12

(1:0�0:020�0:052)

UncertaintiesfromOPEandbquarkmass(�90MeV)

Hoangetal.(1999)andUraltsevetal.(1998)

Di�erentstrategiesforbeatingdownthebackground

ChoiceofKinematicCuts

�E`

>�2:4GeV(keepsabout5{10%ofb!u`�)

�q2>�12GeV2(keepsabout20%)

�MX

<MD

(keepsabout70%)

Butthesecutsintroduceadditionaluncertainties

8May2002


29


OPAL EPJ C21 (2001) 399

10 3

10 4

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

OPAL data --- MC, no b → u l ν

χ2/ndf = 14.6/9a)

Neural Network Output

Ent

ries

/ 0.1

-50

0

50

100

150

200

250

300

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

a)

MC, b → u l νOPAL data

Ent

ries

/ 0.1

Neural Network Output

Huge background suppressed with 7 variable Neural Net

Small signal extraction depends on b! c`� model! S=B = 0:05



ALEPH EPJ C6 (1999) 555

10 3

10 4

0 0.2 0.4 0.6 0.8 1

b → u l νb → c l νb → c → lotherev

ents

/ 0.

1

a)

NNbu

ALEPH

0

500

1000

1500

2000

2500

0 0.2 0.4 0.6 0.8 1

b)

NNbu

-100

0

100

200

0 0.2 0.4 0.6 0.8 1

Dat

a -

Mon

te C

arlo

c)

NNbu

-100

0

100

200

0 0.2 0.4 0.6 0.8 1

d)

NNbu

20 varariable NN

S=B = 0:07



DELPHI PLB 478 (2000) 14

0

500

1000

0 0.5 1 1.5 2 2.5 3

0

500

1000

1500

2000

0 0.5 1 1.5 2 2.5 3

MX (GeV/c2)

MX (GeV/c2)

MX (GeV/c2)

dN/N

0

0.05

0.1

0.15

0.2

0 0.5 1 1.5 2 2.5 3

-40

-20

0

20

40

60

80

0 0.5 1 1.5 2 2.5 3

E* Lepton (GeV)

Dat

a -

Bac

kgro

und

MC

E* Lepton (GeV)

Dat

a -

Bac

kgro

und

MC

-40

-20

0

20

40

60

80

0 0.5 1 1.5 2 2.5 3

Use charm vertex to suppress bkgd

MX < 1:6 signal region

S=B = 0:10



Inclusive jVubj - LEP Summary0 1 2 3 4 5 6

BR(B → Xu l υ) x 103

LEP Average 1.71 ± 0.31 ± 0.37 ± 0.21

OPAL 1.63 ± 0.57 ± 0.48 ± 0.25

L3 3.3 ± 1.3 ± 1.4 ± 0.5

DELPHI 1.69 ± 0.54 ± 0.39 ± 0.25

ALEPH 1.73 ± 0.56 ± 0.51 ± 0.21

LEP jVubj Working Group



jVubj from lepton spectrum and b! s

dΓ(b→c)/dEe

10 dΓ(b→u)/dEe

Ee (GeV)

dΓ/d

E e

∆E

0 1 2

To measure b! u`�

Must suppress b! c`�

Cutting on E` introduces problems:

� Large model dependence

(What fraction above cut?)

� At edge of spectrum

sensitive to b quark motion

Idea:1 Reduce problems by using b! s photon spectrum

Common shape function for b! light transitions (to leading order)

Tells how to smear from b! s to B ! Xs and b! u`� to B ! Xu`�

1(Neubert, Kagan, De Fazio ; Leibovich, Low, Rothstein)



SemileptonicB


jVub jfrom

leptonspectrum

andb!

s

MeasureB!Xu`�inaleptonmomentuminterval(p)atthe�B!X`��

endpoint

��Bub (p)isthebranchingfractionforB!Xu`�in(p),

�fu(p)isthefractionoftheB!Xu`�spectrumin(p),and

�Bub �B(B!Xu`�)istheB!Xc `�branchingfraction.

New

m

easurem

entoffu(p)

��tb!s datatoashapefunction(Kagan-Neubert)

�useshapeparameterstodeterminefu(p)(DeFazio-Neubert)

ThengetBub

from�Bub (p)=fu(p)Bub

andobtainjVub jfrom

jVub j= h(3:07�0:12)�10�3 i� �Bub

0:001

1:6ps

�B

�12

(Hoang-Ligeti-Manohar)(Bigi-Uraltsev-Shifman-Vainshtein)

8May2002


35


jVubj from lepton spectrum and b! s

Lept

ons

/ (50

MeV

/c)

5000

2500

1500

3000

0

0

3.002.752.502.252.00Momentum (GeV/c)

( a )

( b )

0970102-001

In (2:2 < p` < 2:6) GeV/c

� suppress and subtract q�q

� subtract B ! Xc`� yield

� Nub = 1901� 122� 256

B ! Xu`� events

� �Bub = (2:35�0:15�0:35)�10�4

� From the b! s spectrum

fu = 0:130� 0:024� 0:015

Improvement on fu from use of b! s spectrum {

knowledge of non-perturbative QCD in B to light decays

jVubj = (4:08� 0:34exp � 0:44fu � 0:16� � 0:24�=MB

)� 10�3

Improved 15% uncertainty CLEO hep-ex/0202019 (to appear in PRL)



BABAR lepton endpoint PRELIMINARY

10

10 2

10 3

10 4

10 5

(a)B A B A R

-1000

0

1000

2000

3000

1.5 2 2.5 3 3.5

(b)

Electron Momentum (GeV/c)

Num

ber

of T

rack

s / 5

0 M

eV/c

(20.6 fb�1 )

Similar to CLEO (9.1 fb�1)

Less O�-�(4S) data

(2.6 fb�1 vs 4.35 fb�1)

Fit q�q to subtract

solid=data open=B �B bkgd

hist=b! u`� ISGW2

�Bub(2:3{2:6 GeV/c) = (0:152� 0:014� 0:014)� 10�3

Good agreement with CLEO �Bub = (0:143� 0:010� 0:014)� 10�3



SemileptonicB


SummaryandOutlook

jVcb j

�agreement(?)inclusiveandexclusivetechniquessub5%

�datainhandatBfactoriestoputourunderstandingtothetest

�ExclusiveFuture

{unquenchedlatticeforF(1)

{dataonformfactorR1 ,R2 ,shape

�InclusiveFuture

{newB,�fromBelleandBabar

{lookspromisingbutneedcon�rmationwithmoremoments

{E-momentsinthesummer

8May2002


38


SemileptonicB


jVub j

�againgoodagreementoninclusiveandexclusive15{20%

�ExclusiveFuture

{MorestatisticsfromBelle,Babar,CLEO

{Latticeformfactorfor�`�

�InclusiveFuture

{bettershapefunctionfromb!s statistics

{useofMX

andq2cuts-isthereargreement?

{bettercontroloftheoryuncertainties?

{highertwistcorrectionstoshapefunction?

{betterb!c`�improvesb!u`�

ManyimprovementsinunderstandingtocomewithBfactorydata.

8May2002


39


SemileptonicB


BackupSlides

8May2002


40


D�`� at �(4S) and Z Experiments

Main di�erences arise from B momentum in lab frame:

At LEP pB � 30 GeV/c; At B �B threshold pB � 0:3 GeV/c

� w is boost of D� in B rest frame

� LEP resolution on �w �0.07{0.14 compared to �w � 0:03 at 4S

Constrained

Unconstrained

w Resolution

entr

ies

/ 0.0

4

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

-0.4 -0.2 0 0.2 0.4 0.6 0.8

DELPHI

2500

2000

1500

1000

500

0

Yie

ld /

0.00

8

wrec - wgen

3071101-034

0.10 0.05 0 0.100.05I I



1.00

0.75

0.50

0.25

01.0 1.51.41.31.21.11.0 1.51.41.31.21.1

0.20

0.25

0.15

0.10

0.05

0

( a ) ( b )

Slo

w P

ion

Effi

cien

cyW

3071001-036

Slo

w P

ion

Mo

men

tum

(G

eV/c

)

� 4S experiments su�er from � eÆciency turn on

At LEP EÆciency is at

{ In D�+ ! D0�+ the � momentum comes from the boost of the D�

{ Low eÆciency below 0.05 MeV - precisely most interesting events for

extrapolation to w=1.

{ Does not apply to D�0 ! D0�0; �0 eÆciency is at.



� LEP expts. have more exposure to B ! D�X`�

{ poorer missing mass resolution { 4S can separate sig/bkgd

{ larger systematic from poorly known B ! D��`� and non-resonant

B ! D��`� modes15000

10000

5000

010 5 0 5

Eve

nts

/ 0.

5

I I

cos ( B

D* )I

3071101-039

CLEO �ts D�X`� systematic=0.3%

BELLE cuts systematic=1.2%

LEP systematic=1.2{5%


cb (ub) w+ - university of pennsylvania · av erage for b! d ` f rom lep j v cb j w orking group up...

Documents