Semileptonic B Decays at the B Factories Concezio Bozzi INFN Sezione di Ferrara Representing Babar...

Semileptonic B Decays at the B Factories

Concezio BozziINFN Sezione di Ferrara

Representing Babar and Belle

At the XL Rencontres de Moriond LaThuile, Italy - March 2006

Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 2

Why?Measurements of |Vub| and |Vcb| from tree level processes

– Constraints on new physics in loops– Treatment of theoretical uncertainties is mature

B

X

c,u

Vcb,Vub

Probe the structure of B mesons – Inclusive decays: b quark mass, momentum

distributions– Exclusive decays: form factors

b ,c u

B,u d

,c uX

W


How?

• Inclusive measurements: |Vcb| & |Vub|– A glimpse on b→s

• Exclusive measurements: |Vcb| & |Vub|– A glimpse on charm SL decays


Inclusive decays: |Vcb|• Heavy Quark Expansion (HQE): double expansion in s and mb

-1

• Fit moments of inclusive distributions – lepton energy, hadron invariant mass– Determine HQ parameters and |Vcb|

• Many measurements from B Factories, CDF, Delphi• Recent measurements from Belle:

),a,m(mf||VΑ)ΑΑ(1||V192π

mGΓ icbOPE2

cbnonpertpertew2

cb3

5bF

clν

),a,m(mfdX

dX)X(X)(EX icb

'OPE

n0

cutn

dX

ddX

d

Depend on scheme, order of expansion

Benson, Bigi, Mannel, Uraltsev, hep-ph/0410080Gambino, Uraltsev, hep-ph/0401063

Benson, Bigi, Uraltsev, hep-ph/0410080

Electron energy, hep-ex/0508056Hadronic mass, hep-ex/0509013

140 fb-1

140 fb-1


b→s helps too… b s

B XS

CLEO

Belle Babar semi

Babar full

Phot

on M

omen

ts

Warning: Some debate going on:Spectrum? Moments?

Normalization Scheme? OPE? DGE?

Buchmueller, Flaecherhep-ph/0507253

0th moment 2nd moment


ResultsGlobal fit in thekinetic scheme

|Vcb| @ 2%mb < 1%mc @ 5%

Buchmüller, Flächerhep-ph/0507253

|Vcb| = (41.96 ± 0.23 ± 0.35 ± 0.59) 10-3

mb = 4.590 ± 0.025 ± 0.030 GeV

mc = 1.142 ± 0.037 ± 0.045 GeV

μπ2 = 0.401 ± 0.019 ± 0.035 GeV2

μG2 = 0.297 ± 0.024 ± 0.046 GeV2

ρD3 = 0.174 ± 0.009 ± 0.022 GeV3

ρLS3 = -0.183 ± 0.054 ± 0.071 GeV3

BRclv = 10.71 ± 0.10 ± 0.08 %

exp HQE ΓSL

b→sγb→clνcombined

b→clνcombined

Based on:Babar: • PRD69, 111103 (2004)• PRD69, 111104 (2004)• PRD72, 052004 (2005)• hep-ex/0507001Belle:• PRL93, 061803 (2004)• hep-ex/0508005CLEO: • PRD70, 032002 (2004) • PRL87, 251807 (2001) CDF: PRD71, 051103 (2005)DELPHI: EPJ C45, 35 (2006)


Inclusive decays: |Vub|

• Unfortunately:

• Kinematic cuts needed:

• Smaller acceptances, theory uncertainties increase– OPE breaks down – “shape function” to resum non-perturbative physics

• Strategy to minimize theory uncertainties: – maximize acceptance, or – choose “smart” regions/variables

• measure partial branching ratio B• get predicted partial rate (p) from theory

2

15

22

2

3( )22

9119

F u

b

b b su

Gm

V mB X

O Theoretical uncertainty ~5%

2

2

( ) 1( ) 50

ub

cb

Vb ub c V

2q

b c

b u

E

b c

b u

Xm

b cb u

Not to scale!

uX

B

q2 = dilepton mass squared

mX = hadron system mass

El = lepton energy

Close friends to the previous ones


Electron endpoint• First |Vub| measurement

– CLEO, November 1989 – Eℓ> 2.3 GeV, (p)~8%

• Precise knowledge of BB backgrounds

– Belle: Eℓ> 1.9GeV, (p)~30% – Babar: Eℓ> 2.0GeV, (p) ~25%– Smaller uncertainties from

theory• Typical requirements: missing

momentum, event shape• S/B~1/10, ~40%

Predicted partial rate from • HQE fits • Bosch et al. hep-ph/0402094,0504071

hep-ex/0504046

PRD73 (012006), hep-ex/0509040

88M BB2.0 GeV < El <2.6 GeV

fully corrected

spectrum


Hadronic B tag• Fully reconstruct one B• Study the recoiling B

– Known momentum and flavour• Access to all kinematic variables

BBrecoreco

BBrecoilrecoilXXuu ll

ee--

DD**

ee++

MX<1.7GeV,q2>8GeV

P+=EX-|pX| >0.66

hep-ex/0505088

hep-ex/0507017

MX<1,7GeV, q2>8GeV

MX<1,7GeV

|Vub|=

S/B~2 ~10-3

253M BB

210M BB

253M BB |Vub| = (4.70 ± 0.24stat ± 0.28syst ± 0.20SF +0.23-0.24th) × 10-3

|Vub| = (4.09 ± 0.19stat ± 0.20syst ± 0.18SF +0.14-0.16th) × 10-3

|Vub| = (4.19 ± 0.20stat ± 0.30syst ± 0.24SF +0.14-0.15th) × 10-3


Reducing model dependence• Relate charmless SL rate to b→s spectrum

• Reduced dependence from shape function• Recoil analysis on 88M BB

2

2 ( ) ( )( ) ub su

ts

W EV d B XB X dE

dEV

Weight function

Leibovich, Low, Rothstein hep-ph/0005124,0105066

mX cut

LLR : MX < 1.67 GeV: |Vub| = (4.43 ± 0.38stat ± 0.25syst ± 0.29theo) 10-3

OPE: MX < 2.50 GeV: |Vub| = (3.84 ± 0.70stat ± 0.30syst ± 0.10theo) 10-3

hep-ex/0601046

theory uncertainties

NEW!


Inclusive |Vub|: summary & outlookBabar (no SF)4.43 ± 0.45 ± 0.29

• Uncertainty on shape function parameters: 4.5%– mb~40 MeV– reduce SF dependence?

• Leibovich-Low-Rothstein hep-ph/0005124, 0105066• Lange-Neubert-Paz (JHEP 0510 (2005) 084), Lange (hep-

ph/0511098)• Other theory uncertainties ~5%

– Subleading SF: 3.5%– Weak annihilation: 2%, can be studied experimentally– Different theory approaches?

• Andersen-Gardi JHEP 0601 (2006) 097• Aglietti, Ferrara, Ricciardi hep-ph/0507285, 0509095,

0509271• Experimental uncertainties:

– Statistics: 2%– Detector systematics: 2.6%– Background modeling: 2%– Signal modeling: 2.2%

hep-ex/0601046 not included yet in

HFAG average

WARNINGvalues and errors adjusted by HFAG.

HQ parameters from hep-ex/0507243, predicted partial rates from hep-ph/0402094,0504071

|Vub| @ ~8%


How?

• Inclusive measurements: |Vcb| & |Vub|– A glimpse on b→s

• Exclusive measurements: |Vcb| & |Vub|– A glimpse on charm SL decays


Exclusive |Vcb|• Well-established method:

• F(1)=1 in the heavy quark limit; lattice QCD says: • Shape of F(w) unknown• Parametrized with 2 (slope at w = 1) and form factor ratios

R1, R2 ~ independent on wuse Caprini-Lellouch-Neubert

• Determine 2, R1, R2 via multi-dimensional fit to helicity amplitudes:

• H+,-,0 are functions of 2, R1, R2

wwVG

dwDBd cbF GF

482

3

22*

Phase space

Form factor

D* boost in B rest frame 0.0300.035(1) 0.919

FHashimoto et al, PRD 66 (2002) 014503

Nucl. Phys. B 530, 153 (1998)


New Babar measurement

stat. MC stat. syst.

Factor 5 improvement on FF uncertainty from previous CLEO measurement (1996!)

Reduced uncertainty on |Vcb| +2.9% -2.6% ± 0.5%

Total systematic error on |Vcb| 4.5% 3.5%

Systematic uncertainty on |Vub| for endpoint analyses is also reduced

hep-ex/0602023

NEW!

1D projections of fit result:

80 fb-180 fb-1


Exclusive |Vub|

• Experimentally:– Good S/B ratio, untagged analyses– Small branching fractions– Measure q2 dependence, compare to

theory

22 223

2 3

( )24

( )Fub

Gd B V fdq

qp

• Theoretically:– Uncertainties complementary to

inclusive approach– FF normalization dominates the error on

|Vub| (~10% for all models)

Calculations of f+(q2):– LQCD (q2>16) – Light-cone sum rules (q2<14)– Quark models (ISGW2)

MES for -0.15 < E < 0.25 GeV

Continuumclul crossfeed

Bl 83 x 106 BB

= missing

of the event ,E p

Fit of signal yield using B mass and E in bins of q2.

Babar untagged analysis: hep-ex/0507003


(Selected) results

253 fb-1

l

— Ball’01 — ISGW2 — UKQCD

d/d

q2 /

tot x

104

d/d

q2 /

tot x

104

l

q2 q2

D*lv tag

hep-ex/0507003

hep-ex/0508018

Lattice and LCSR

favored over ISGW2

untagged

80 fb-1


Summary of exclusive |Vub|

• Tagged: S/B~3, untagged: S/B~1• Comparable precision • Tagged measurements will improve

– statistical component in significant systematic uncertainties

|Vub| averages based on different models


Validate theory with D→K/l

80 fb-1

80 fb-1

NEW!

More results from CLEO-c this afternoon


Conclusion• Semileptonic B decays: very active area for both theory

and experiment• Substantial progress in HQE fits to inclusive decays:

– precise measurements of |Vcb|, mb and HQ parameters relevant to other decays

• Exclusive/inclusive determinations of |Vcb| in agreement • Increased precision in inclusive |Vub|

– improved measurements, – more comprehensive theoretical treatment– better determination of mb.

• Studies of exclusive charmless decays are improving as datasets increase. – Reducing the theoretical uncertainties to a comparable level is

challenging.


Backup


Inclusive decays: |Vcb|• Heavy Quark Expansion (HQE): double expansion in s and mb

-1

• Fit moments of inclusive distributions – lepton energy, hadron invariant mass– Determine HQ parameters and |Vcb|

),a,m(mf||VΑ)ΑΑ(1||V192π

mGΓ icbOPE2

cbnonpertpertew2

cb3

5bF

clν

),a,m(mfdX

dX)X(X)(EX icb

'OPE

n0

cutn

dX

ddX

d

Depend on scheme, order of expansion

Lept

on M

omen

ts

Had

ron

Mom

ents

Ecut (GeV)Buchmueller, Flaecher

hep-ph/0507253

Benson, Bigi, Mannel, Uraltsev, hep-ph/0410080Gambino, Uraltsev, hep-ph/0401063

Benson, Bigi, Uraltsev, hep-ph/0410080


Results• Global fit (in the kinetic scheme) gives:

|Vcb| @ 2%mb < 1%mc @ 5%

hep-ph/0507253

|Vcb| = (41.96 ± 0.23 ± 0.35 ± 0.59) 10-3

mb = 4.590 ± 0.025 ± 0.030 GeV

mc = 1.142 ± 0.037 ± 0.045 GeV

μπ2 = 0.401 ± 0.019 ± 0.035 GeV2

BRclv = 10.71 ± 0.10 ± 0.08 %

exp HQE ΓSL

Eℓ, hep-ex/0508056Hadronic mass, hep-ex/0509013• Recent measurements from Belle (to be included)

unfolded

0.4 GeV!

Stat. erro

rs only!


Hadronic B tag• Fully reconstruct one B• Study the recoiling B

– Known momentum and flavour• Access to all kinematic variables

BBrecoreco

BBrecoilrecoilXXuu ll

ee--

DD**

ee++

MX<1.7GeV,q2>8GeV

P+=EX-|pX| >0.66

hep-ex/0505088

hep-ex/0507017

MX<1,7GeV, q2>8GeV

MX<1,7GeV

|Vub|=

S/B~2 ~10-3

253M BB

210M BB

253M BB


Validate FF calculations with D→K/l

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