1. EXPERIMENTAL UPDATE ON |Vcb| (EXCLUSIVE) Arantza Oyanguren
( DELPHI - Valencia )
CKM WORKSHOP ‘03

2. |Vcb| FROM B D *l -  l Vcb From the s.l. decay width: q2 nl c b1
|Vcb| FROM B D *l - 
Vcb q2 l nl c b
From the s.l. decay width:
Known function
(Phase space)
Form factor of the B D* transition 
 Normalized by HQET (mQ  ) at q2max (w = 1) 
 1/ mQ and QCD corrections 
FD*(1)=1
FD*(1)= 0.91  0.04 *
* PDG ‘02
CKM ‘03
A. Oyanguren

3. SIGNAL RECONSTRUCTION2
SIGNAL RECONSTRUCTION
BABAR
(4S) BB
pB ~ 30 GeV
BELLE
pB ~ 1 GeV
ALEPH
DELPHI
OPAL
CLEO
Z  bb
pB ~ 0.3 GeV
CKM ‘03
A. Oyanguren

4. SIGNAL RECONSTRUCTION m= m(D0) -m(D0) ~ m(soft)3
SIGNAL RECONSTRUCTION
B  D* l - 
@ LEP p  1.0 GeV
@ (4S) p  0.1 GeV
D *- lepton candidates :
D0 soft
m= m(D0) -m(D0) ~ m(soft)
K- +
K- + + -
K- +0
Ks0 + -
Inclusive D0
Exclusive D0
OPAL
BABAR
CKM ‘03
A. Oyanguren

5. E, p conservation, vertex info...4
w RECONSTRUCTION
Efficiency:
E, p conservation, vertex info...
From decay products
From missing energy
Measured
LEP: ~
w Resolution:
(4S): ~ 0.03
ALEPH w
CKM ‘03
A. Oyanguren

6. BACKGROUND Disentangling D * ’s coming from D ** states... @ (4S)5
BACKGROUND
Disentangling D * ’s coming from D ** states...
b  D*+ X l_ l
@ (4S)
@ LEP
~ 66% charged particles
D*l  (73.5%)
D**l  (7.5%)
Fake lep (0.3%)
Uncorr (6.2%)
Correlated (1.5%)
Contin. (3.2%)
Fake D* (7.75%)
ElectronsK
BABAR
cosB,D*l
topology info
events/0.27
 data
D*l 
D**l 
Comb. Bg.
DELPHI
events/01
OPAL
CKM ‘03
A. Oyanguren

7. 6
FITS TO|Vcb|
 Parametrization of the form factor F(w) from I. Caprini,
L. Lellouch, M. Neubert [NPB 530, 153 ‘98]* as a function
of the slope form factor 2 and the form factor ratios R1
and R2 (measured by CLEO [PRL 76, 3898 ‘96] ).
 Fit d/dw to extract F(1)|Vcb| and 2 w w
BELLE
CLEO
Entries/0.05
FD*(1)|Vcb|
* See also C.G. Boyd, B. Grinstein, R.F. Lebed [PRD 56, 6895 ‘97]
CKM ‘03
A. Oyanguren

8. STATISTICS Analyzed events : OPAL D* l candidates DELPHI CLEO ALEPH7
STATISTICS
Analyzed events :
OPAL
D* l candidates
DELPHI
CLEO
ALEPH
BELLE
Statistical error
BABAR
ALEPH
DELPHI
OPAL
CLEO
BELLE (partial stat.)
BABAR
(expected)
Vcb/Vcb (%)
CKM ‘03
A. Oyanguren

9. SYSTEMATICS 8a @ LEP @ (4S) CKM ‘03 A. Oyanguren BABAR (BR) BELLE
Moriond EW ‘03
BELLE
PLB 526, 247 ‘02
hep-ex/
CLEO
@ (4S)
CKM ‘03
A. Oyanguren

10. 8b
SYSTEMATICS
@ LEP
hep-ex/
CKM ‘03
A. Oyanguren

11. 8c
SYSTEMATICS
@ (4S)
CLEO
CKM ‘03
A. Oyanguren

12. SYSTEMATICS BABAR (BR) BELLE @ (4S) 8d Moriond EW ‘03
PLB 526, 247 ‘02
CKM ‘03
A. Oyanguren

13. UPDATED WORLD AVERAGE Winter ‘03 PDG ‘03 Using F(1)=0.91  0.04
F(1)|Vcb| = (38.1  1.0) 10-3
r2 =1.57  0.14
PDG ‘03
F(1)|Vcb| = (38.8  0.5(stat).  0.9(sys.)) 10-3
r2 =1.49  0.05(stat.)  0.14(sys.)
2/d.o.f.=1.7
CL=6.9%
 Analyses rescaled to common parameters:
Using F(1)=0.91  0.04
|Vcb|= (42.6  0.6(stat)  1.0(sys)  2.1(th.)) 10-3
(Thanks to E. Barberio and U. Langenegger (HFAG) for the averages)
CKM ‘03
A. Oyanguren

14. |Vcb|= (42.4  3.7(exp.)  3.0(th.))10-3
|Vcb| FROM B D l - 
CLEO
BELLE
D0, D+ D+
ALEPH D+
BELLE
Winter ‘03
G(1)|Vcb| = (41.9  3.7) 10-3
rD2 =1.15  0.16
Using G(1)=1.00  0.07
PDG ‘03
G(1)|Vcb| = (42.4  3.7) 10-3
rD2 =1.14  0.16
2/d.o.f.=0.06
CL=99%
|Vcb|= (42.4  3.7(exp.)  3.0(th.))10-3
CKM ‘03
A. Oyanguren

15. 11
CONCLUSIONS
 |Vcb| from exclusive measurements limited by systematics from several sources and theory
 large systematics are correlated between experiments: B(b B0), B((4S) B0 B0), D BR’s, D ** contribution, R1 and R2 form factors...
CKM ‘03
A. Oyanguren

16. 12
PERSPECTIVES
 Waiting for BABAR results, and BELLE with larger analyzed statistics,
 waiting for more accurate lattice computations of FD*(1) and GD(1),
 the control of the main systematics by additio-nal measurements
 and CLEO-c results on D BR’s
CKM ‘03
A. Oyanguren