1. David Côté, Université de Montréal for the BABAR collaboration
Semileptonic B decays, B mixing and magnitudes of CKM elements at BABAR
David Côté, Université de Montréal
for the BABAR collaboration
DAΦNE 2004: Physics at meson factories

2. David Côté, Université de Montréal
Outline
88106 BB
∫ Lon dt = 82 fb-1
Results presented today used less than half of the data we have now.
|Vcb|
|Vub|
B0 – B0 mixing
semileptonic
B decays: BXc l  or BXu l 
md, ...
DAΦNE 2004
David Côté, Université de Montréal

3. Why studying semileptonic B decays and B0 - B0 mixing?
To (over-)constrain the Standard Model and determine some of its fundamental parameters: mb, mc and CKM matrix elements
To know more precisely parameters needed by other analyses (md, branching fractions, form factors,...)
To learn about QCD and effective QCD
DAΦNE 2004
David Côté, Université de Montréal

4. Inclusive |Vcb| measurement strategy
f , f0 : heavy quark expansion (HQE) formulae*
mb and mc : running quark masses (at  = 1 GeV)
G, , LS, D : non-perturbative QCD parameters
*Gambino & Uraltsev
hep-ph/
hep-ph/
Problem: large uncertainties in mb, mc, ’s and ’s
Solution: Measuring mb, mc, G, , LS, D, simultaneously to Br(BXc e ) and |Vcb| using HQE’s predictions of El and MXc moments.
i=1..3
i=1..4
DAΦNE 2004
David Côté, Université de Montréal

5. electron energy moments
Strategy: identify B  Xc e  decays with di-electron events
Require typical B-B event topology, one high momentum etag and one opposite charge esig
Subtract remaining backgrounds (mostly from data control samples)
Corrections applied for Bremsstrahlung, e ID efficiency, etc.
esig e- e+
Btag
Bsig ν
etag
Data sample:
∫ L dt = 47.4 fb-1
400,000 events!
Accepted by Phys. Rev. D
hep-ex/
esig energy spectrum used for moments measurement
DAΦNE 2004
David Côté, Université de Montréal

6. David Côté, Université de Montréal
hadronic mass moments
Strategy: identify B  Xc l  decays on the recoil of fully reconstructed B’s
Semileptonic side requirements :
exactly one e or  with p* > 0.9 GeV/c
Emiss, Pmiss consistent with a neutrino and net event charge  1
MXc reconstructed with a kinematic fit to all remaining particles
Corrections for small MXc reconstruction bias computed from Monte Carlo
Accepted by Phys. Rev. D
hep-ex/
BABAR
El* > 0.9 GeV D* l p e+
Breco
Brecoil Xc ν e-
Clear sign of higher charm resonances
DAΦNE 2004
David Côté, Université de Montréal

7. David Côté, Université de Montréal
Fit results
Accepted by
Phys. Rev. Lett.
hep-ex/
MXc and El moments as a function of minimum El cut
χ2 = 15
Ndof = 20
used in global fit
not used in global fit
Excellent agreement between lepton and hadron moments!
Excellent agreement between data and HQE predictions!
DAΦNE 2004
David Côté, Université de Montréal

8. |Vcb|: result and comparison
2% error on |Vcb|!
|Vcb|
Br(BX l )
DAΦNE 2004
David Côté, Université de Montréal

9. mb, mc: result and comparison
kinetic mass
scheme
theory
Conversion of mb and mc from kinetic mass to MS scheme by N. Uraltsev (hep-ph/ , hep-ph/ , hep-ph/ )
DAΦNE 2004
David Côté, Université de Montréal

10. David Côté, Université de Montréal
Inclusive |Vub|
Phys. Rev. Lett.
92:071802,2004
Strategy: same B  X l  selection as hadron mass moments (slide 6)
BXu l  selection: kaon veto, low MX
Measurement of for systematic errors cancellation
Monte Carlo
∫ L dt = 82 fb-1
*Br(BXu l ) extracted from Ru using ref Phys.Rev.D67:031101,2003
Several avenues currently considered in order to reduce further the theoretical uncertainties.
DAΦNE 2004
David Côté, Université de Montréal

11. David Côté, Université de Montréal
Exclusive |Vub|
Phys. Rev. Lett.
90:181801,2003
Strategy: untagged identification of B e  decays with “ reconstruction”
Signal extracted by requiring:
very high momentum electron
E = Ebeam - E - El - Emiss compatible with zero
M compatible with  mass
Rather high theoretical uncertainties (~15%)
Relatively high yield: 834  102 events (only electrons and 50.5 fb-1)
exclusive
analysis
advantage MC
GeV/c
∫L dt = 50.5 fb-1
Much more to be expected soon:
larger dataset
additional decay modes
reduced theoretical uncertainties
form factor(s) measurement
new recoil techniques
DAΦNE 2004
David Côté, Université de Montréal

12. David Côté, Université de Montréal
« classic » B0 - B0 mixing
(1) Phys.Rev.Lett.88:221802,2002
(2) Phys.Rev.Lett.88:221803,2002
(3) Phys.Rev.Lett.89:011802,2002
(4) Phys.Rev.D66:032003,2002
(5) Phys.Rev.D67:072002,2003
The B0 – B0 mixing technique is well-known and well-documented:
Determination of vertex and flavor of the two B’s
“t” between the two B’s estimated from distance between vertices
“mixed”
“unmixed”
Results (23106 BB):
(3)
(averaged 1,2,5)
DAΦNE 2004
David Côté, Université de Montréal

13. Generalized B0 - B0 mixing analysis
B0 – B0 total decay-rate difference, CP violation in mixing and CPT violation were always neglected in mixing and CP measurements
The validity of these assumptions was recently confirmed in a generalized B0 - B0 mixing analysis using 82 fb-1
ACP (ACP) is the amplitude
for B0fCP (B0fCP)
d/d : lifetime difference between BH and BL mass eigenstates (not “Bshort” and “Blong”)
(): difference between
flavor (mass) eigenstates
z  (0,0): imply CPT violation
|q/p|  1: imply
Phys.Rev.Lett.92:181801,2004
hep-ex/ , submitted to PRD
DAΦNE 2004
David Côté, Université de Montréal

14. David Côté, Université de Montréal
Summary
New BaBar precision measurement of |Vcb|, Br(BXc l ), mb, mc and 4 HQE parameters.
13% (18%) inclusive (exclusive) |Vub| measurement at BaBar using BXu l  decays (currently dominated by theory errors, but much progress to be expected soon).
New measurement of d/d, |q/p| and z generalized mixing parameters validate the assumptions used for previous BaBar’s mixing and CP measurements.
DAΦNE 2004
David Côté, Université de Montréal

15. backup slides

16. David Côté, Université de Montréal
- plane
DAΦNE 2004
David Côté, Université de Montréal

17. David Côté, Université de Montréal
md,s vs Vtd,s
 [known factors]
needs latttice QCD calculations
 [known factors]
also needs latttice QCD calculations,
but easier to compute.
DAΦNE 2004
David Côté, Université de Montréal

18. electron energy moments
Defining:
We measured...
the first moment:
the central moments:
n = 2,3
the partial branching fraction (0th moment):
DAΦNE 2004
David Côté, Université de Montréal

19. David Côté, Université de Montréal
HQE parameters
We use calculations in kinetic mass scheme by Gambino and Uraltsev
(HQE to order 1/mb3, as2 )
μπ2 - exp. value of kinetic energy of b quark inside B meson
μG2 - exp. value of chromomagnetic moment operator
ρD3 - exp. value of Darwin operator
ρLS3 – exp. value of Spin-Orbit operator
hep-ph/
hep-ph/
Ơ(1/mb2){
Ơ(1/mb3){
DAΦNE 2004
David Côté, Université de Montréal