Semileptonic B Decays at the B Factories Concezio Bozzi INFN Sezione di Ferrara Representing Babar...
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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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 3
How?
• Inclusive measurements: |Vcb| & |Vub|– A glimpse on b→s
• Exclusive measurements: |Vcb| & |Vub|– A glimpse on charm SL decays
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 4
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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 5
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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 6
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)
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 7
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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 8
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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 9
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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 10
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!
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 11
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%
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 12
How?
• Inclusive measurements: |Vcb| & |Vub|– A glimpse on b→s
• Exclusive measurements: |Vcb| & |Vub|– A glimpse on charm SL decays
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 13
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)
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 14
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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 15
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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 16
(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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 17
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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 18
Validate theory with D→K/l
80 fb-1
80 fb-1
NEW!
More results from CLEO-c this afternoon
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 19
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.
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 20
Backup
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 21
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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 22
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!
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 23
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
Moriond EW, March 2006 Semileptonic B decays - Concezio Bozzi 24
Validate FF calculations with D→K/l