1. Review of |Vcb| and |Vub| measurements
Fabrizio Bianchi
University of Torino and INFN-Torino
Rencontres de Moriond EW 2009
La Thuile, 7-14 March 2009

2. Outline Introduction to the measurement of |Vcb| and |Vub|
Results from the B-factories:
|Vcb| from Spectral Moment
FF x|Vcb| from B D(*)ln
Inclusive |Vub|
|Vub|from exclusive SL charmless B decays
Summary and outlook

3. Constraints on Unitarity Triangleh a g b r
A precise determination of |Vub/Vcb| is crucial to be able to
observe deviations from the CKM mechanism due to New Physics

4. Semileptonic B Decays
|Vcb| and |Vub| are determined from semileptonic B decays.
At tree level everything is nice and clean.
|Vcb| , |Vub|
QCD corrections must be included.
Inclusive measurements: OPE
Exclusive measurements: Form
Factors from LQCD B
Xc , Xu

5. |Vcb| from Spectral Moments

6. OPE: Semileptonic Width
Wilson coefficients f, k, g, d, l can be calculated in
perturbation theory.
Non-perturbative parameters μπ , μG , ρD , ρLS are matrix
elements of local operators in HQET.

7. OPE: Other Observables
OPE for moments involves same matrix elements
and different, calculable Wilson coefficients.

8. Moment Analysis Moment Measurements Fit μπ μG ρD ρLS OPE Expressions
|Vcb| mb mc
μπ μG ρD ρLS
Fit
OPE
Expressions
External input: average B lifetime tB = ( / ) ps
Kinetic running mass
P.Gambino, N.Uraltsev, Eur.Phys.J. C34, 181 (2004)
D.Beson, I.Bigi, N.Uraltsev, Nucl.Phys. B710, 371 (2005)
1S mass
C.Bauer, Z.Ligeti, M.Luke, A.Manohar, M.Trott, Phys.Rev. D70, (2004)

9. Belle Results
Fit in the Kinetic Scheme
Phys. Rev. D78, (2008)

10. Belle Results

11. |Vcb| - HFAG Average Bell Moment Analysis not included
Adding Xsg Moments lowers mB
Belle result don’t show this effect
mB is input to |Vub| extraction !!!
Kinetic Scheme
Kinetic Scheme
Low c2/ndf
Are theoretical correlation properly accounted ?

12. FF x|Vcb| from B D(*)ln

13. VCB & Form Factors: HQET expansion of width:
Caprini et al. Parametrization of FF (Nucl.Phys.B 530 (1998), 153):
Experiments measure:
|Vcb|*FF(w→1)
 r2D, r2D* ( slopes of FF )
R1,R2 : form factor ratios (D*)

14. Untagged Analysis arXiv:0810.1657 [hep-ex] 140 fb-1 Decay chain:
Measure helicity angles (Ql, QV, c)
Fit:

15. Untagged Analysis Phys.Rev.D79:012002,2009 207 fb-1
Select D0(Kp)lnX, D+(Kpp)lnX events with pl > 1.2 GeV/c
Get D/D* rates with a binned
3-d fit to pl, pD, cosQBY
Relate BR(B0) to BR(B+)
using lifetime ratio
Extract from the fit:
r2D, r2D*, BF
Compute:
|Vcb|*F(1), |Vcb|*G(1)

16. Hadronic Tag Analysis arXiv:0807.4978 [hep-ex] 417 fb-1 D0
Select D0ln, D+ln decays
on the recoil of a fully
reconstructed B
Event yields from a fit
to MM2 in 10 w bins D+
G(1) |Vcb| and r2G from a
fit to w distribution
MM2 = (PB−PD−Pl)2 [GeV2/c4]

17. Hadr Tag Analysis arXiv:0808.0528 [hep-ex] 417 fb-1
Important to reduce systematic in |Vcb| excl. measurements.
Discrepancy between B->Xcln inclusive rate and sum of exclusive modes.
M(D(*)p – m(D(*)) [GeV/c2]

18. VCB & Form Factors: Averages
C. Bernard et al., arXiv: [hep.lat]
M. Okamoto et al., Nucl. Phys. Proc. Suppl. 140, 461 (2005)
VCB & Form Factors: Averages

19. Open Issues on |Vcb| Measurements
|Vcb| from Moment Analysis
Belle recent results in good agreement with HFAG average
Open questions on HFAG global fit:
Inclusion of the B ->Xs g data lowers the b-quark mass mb
c2/ndf = 29.7/57 (24.1/46) Too small ?
F(1)|Vcb| and G(1)|Vcb| from B->D(*)ln
Good agreement between experiments
|Vcb| extracted using LQCD 2s lower than result from
Moment Analysis

20. |Vub| from Inclusive
Semileptonic B Decays

21. Inclusive |Vub| Measurement I
Charm background ~50x larger than signal
Use kinematics to distinguish Xu signal from Xc BG (mc >> mu)
● ELEP = lepton energy
● q2 = momentum transfer squared = (pB-pX)2 = (pl+pn)2
● mX = mass of the hadronic system
● P+ = EX-|pX| = light-cone component of X momentum

22. Inclusive |Vub| Measurement II
Cut away B Xcln loose some B Xuln signal
We measure:
total rate
cut dependent constant
predicted by theory
fraction of signal that pass the cut
Must be corrected for QCD
Use HQE parameters from
B Xcln and B sg to
extrapolate to full phase
space and extract |Vub|
BLNP - B.O. Lange, M. Neubert and G. Paz,
Phys. Rev. D72: (2005)
DGE - J.R. Andersen and E. Gardi, JHEP 0601:097 (2006)
GGOU - P. Gambino, P. Giordano, G. Ossola, N. Uraltsev,
JHEP 0710:058,2007
BLL - C.W. Bauer, Z. Ligeti and M.E. Luke,
Phys. Rev. D64: (2001)

23. BaBar: Hadronic tag technique
PRL 100, (2008)
BaBar: Hadronic tag technique
B → Xu l n
B → Xc l n (bkgd)
B → Xu l n (outside
selected region)
Background subtracted
BLNP
DGE
Mx<1.55 GeV/c2
BLNP
DGE
P+<0.66 GeV/c2
BLNP
DGE
BLL
Mx<1.7 GeV/c2
Q2>8.0 GeV2/c2

24. Belle Multivariate Analysis
Presented at CKM
Belle Multivariate Analysis
Hadronic Tag
Boosted decision tree
based selection, use ~20
event parameters
2D fit to Mx, q2 with
backgrounds and signal
floated

25. Inclusive |Vub|: HFAG averages
Belle multivariate analysis not included
Inclusive |Vub|: HFAG averages
Different |Vub| values from different calculations
Nice agreement of |Vub| measurements

26. |Vub| from Exclusive
SL Charmless B Decays

27. Exclusive |Vub| Measurements
= p, h, h’, r, w
Complementary exp approaches:
Untagged (with n reconstruction)
Semileptonic tag
Hadronic tag
Different systematic errors and independent samples
Different form factor calculations
Perform measurement in q2 bins to reduce model dependency
See Talk of R. Sommer

28. B pln untagged Still most precise measurement PRL 98, 091801 (2007)
206 fb-1
Reconstruct neutrino from full event:
Extract signal yield in 12 q2 bins from fit to ΔE vs. mES distributions
Used by FNAL (arXiv: [hep-lat]) to extract |Vub| = (3.38 +/- 0.36)x10-3

29. B p, h, h’ l n Semileptonic Tag
arXiv: [hep-ex]
B p, h, h’ l n Semileptonic Tag
348 fb-1
Analysis Strategy:
Tag one B in D(*)ln and look for signal in the recoil;
Identify a signal lepton (right charge) and search for a:
p+, p−, p0
h → g g , h → p+ p− p0 , h → p0 p0 p0
h´ → h p+ p−
No additional tracks and low neutral energy;
Extract signal yields with unbinned maximum likelihood fit to cos2 ϕ B.

30. B p, h, h’ l n Semileptonic Tag
arXiv: [hep-ex]
B p, h, h’ l n Semileptonic Tag
348 fb-1
Using isospin relation
3.2 s significance
(90% CL)
CLEO (PRL 99,041802(2007):

31. B p, (r, w) l n Hadronic Tag arXiv:0812.1414 [hep-ex] 605 fb-1
Fully reconstruct the Breco
Know kinematics and flavor of signal B
Extract signal yields from M2miss≈ M2ν
distribution in 3 q2 bins

32. |Vub| from B pln: HFAG average
Consistent results
Form Factor systematic dominates
More exp q2 data to constraint FF

33. Open Issues in |Vub| Measurements
Inclusive measurements:
Nice consistency of |Vub| measurements extracted using the same
calculations
Different |Vub| values are obtained when using different calculations
(d|Vub|/|Vub|)exp ~ 4% (d|Vub|/|Vub|)Th ~ 6-7%
Exclusive measurements:
Uncertainties from Form Factors are the dominant systematic
(d|Vub|/|Vub|)exp ~ 5% (d|Vub|/|Vub|)FF=+17% -11%
Need more data to constraint different calculations
Looking for progress from LatticeQCD
Exclusive measurements give a lower |Vub| than inclusive ones

34. Conclusions Progressing in the understanding of B SL decays
Inclusive |Vcb| precision now at 2% level
Still remaining issues on global fit and B->Xsg data inclusion
Many new results on B->D(*)ln decays
Precision on |Vcb| measurements limited by form factor knowledge
Lower value (2 s) than from inclusive analysis
Inclusive |Vub| measurements now at 8% precision
Limited by calculation of theoretical phase space acceptances
Exclusive |Vub| measurements limited by form factor knowledge
Need more data and progress on theoretical calculation
Puzzle of exclusive vs inclusive |Vub| values not yet solved

35. Backup Slides

36. BABAR Detector

38. Experimental Methods

40. |Vub| from B pln SL Tag DB is the partial branching fraction
arXiv: [hep-ex]
|Vub| from B pln SL Tag
348 fb-1
DB is the partial branching fraction
Dz calculated using:
LCSR for q2<16 GeV2
Lattice QCD for q2>16 GeV2

41. B p, r, w l n Hadronic Tag

42. |Vub| from B pln Hadr. Tag
arXiv: [hep-ex]
|Vub| from B pln Hadr. Tag
605 fb-1
To extract |Vub| use:
LCSR for q2<16 GeV2
Lattice QCD for q2>16 GeV2