1. Semileptonic B-decays (b to u transition)
Outline
Inclusive b to u decays
Exclusive b to u decays
Summary
(nothing new since ICHEP06)
Eunil Won
Korea University
Heavy Quarks and Leptons
16.10 ~ Munich, Germany
HQL06 Munich, Germany E. Won, Korea University

2. HQL06 Munich, Germany E. Won, Korea University
Status of
Measurements of provide
independent crosscheck
of the unitary trangle (UT)
With , can
constrain UT from tree level
processes alone
is established firmly by now
from inclusive measurements
:precision about 7%
accessing fraction of phase space  shape function is usually required
from exclusive decays
:precision worse than 10%
form factor has to be calculated  model dependence is introduced
HQL06 Munich, Germany E. Won, Korea University

3. HQL06 Munich, Germany E. Won, Korea University
from semileptonic B-decays
Semileptonic inclusive rates depend only on CKM matrix element and quark mass u
hadron level easy to calculate in OPE (<5% error)
BaBar PRD (2006)
But the problem is:
OPE does not work on limited phase space
HQL06 Munich, Germany E. Won, Korea University

4. HQL06 Munich, Germany E. Won, Korea University
: inclusive determination
Limited phase space to reduce the b to c transition background OPE fails
Non perturbative Shape Function to extrapolate to the full phase space
Shape function: lightcone momentum distribution function of the b quark inside the meson
Detailed shape not constrained theoretically, in particular the low tail
Shape function need to be determined from experimental data
Theoretical frameworks used by HFAG
BLNP : B. O. Lange, M. Neubert and G. Paz, PRD (2005)
DGE : J. R. Anderson and E. Gardi, JHEP 0601:097 (2006)
BLL : C. W. Bauer, Z. Ligeti and M. E. Luke, PRD (2001)
Also
(*) LLR : A. K. Leibovich, I. Low and I. Z. Rothstein, PLB (2000)
 for BaBar’s new analysis (less dependence on SF)
HQL06 Munich, Germany E. Won, Korea University

5. HQL06 Munich, Germany E. Won, Korea University
Inclusive
 Exploits different kinematics
: lepton energy
: lepton-neutrino mass squared
: mass of the hadronic system
Signal events have smaller and  Larger and
HQL06 Munich, Germany E. Won, Korea University

6. HQL06 Munich, Germany E. Won, Korea University
Lepton Endpoint
CLEO PRL (2002)
Belle PLB (2005)
BaBar PRD (2006)
First pioneered by CLEO
Subtraction of backgrounds crucial!
On resonance data
data
>
CLEO 9/fb
2.30 ± 0.15 ± 0.35
2.1 GeV
Belle 27/fb
8.47 ± 0.37 ± 1.53
1.9
BaBar 80/fb
5.72 ± 0.41 ± 0.65
2.0
BaBar
Off resonance data
(non BB bkg in)
After non-BB bkg
subtraction
Simulated BB
background
BaBar
Partial
branching fraction
After all bkg
subtraction
Simulated
Simulated
HQL06 Munich, Germany E. Won, Korea University

7. HQL06 Munich, Germany E. Won, Korea University
Measurements of
Belle PRL (2005)
BaBar hep-ex/
Reconstruct all decay products to measure
reco-side
Fully reconstruct B meson
- flavor and momentum known
- maximum purity but low efficiency
2) D(*) tag in reco-side
- lower purity but efficiency improved
signal-side
data
Phase space
Belle 253/fb
mX<1.7
12.4±1.1±1.0
mX<1.7,q2>8
8.4±0.8 ±1.0
P+<0.66
11.0±1.0 ±1.6
BaBar 211/fb
8.7±0.9 ±0.9
(preliminary)
Belle
Belle
First measurement of P+ (Belle)
Errors are larger than endpoint results
P+ (GeV)
mX(GeV)
HQL06 Munich, Germany E. Won, Korea University

8. HQL06 Munich, Germany E. Won, Korea University
Extracting from partial branching fraction
(“Morii diagram”)
Inclusive
SSFs
Shape Function
HQE Fit
Inclusive
HFAG main results:
HQ parameters from
and
hep-ph/
duality WA
HQL06 Munich, Germany E. Won, Korea University

9. HQL06 Munich, Germany E. Won, Korea University
Fitting the Shape Function
Belle PRL (2004)
BaBar PRD (2005)
quark level
hadron level
Belle
B Meson
s-quark
b-quark
Inclusive measurement
Easy to fit SF
E*g (CM frame)
Need to parameterize SF
(shape is not known a priori)
BaBar
Sub-leading shape function is considered (BLNP)
HQ parameters can be extracted from the photon spectrum in or
lepton spectrum in
Sum of exclusive decays
Lab frame (K* peak) Eg
HQL06 Munich, Germany E. Won, Korea University

10. Inclusive : BLNP framework
The total error in percentage:
statistical
2.2%
Expt. systematic
2.8%
model
1.9%
1.6%
HQ parameters
4.2%
Subleading SF +
Perturbative
3.8%
Weak Annihilation
Theoretical uncertainty is larger
(not by a lot)
HQL06 Munich, Germany E. Won, Korea University

11. HQL06 Munich, Germany E. Won, Korea University
Inclusive : DGE framework
Dressed Gluon Exponentiation (DGE): on-shell b-quark calculation converted into hadronic variables used as approximation to the meson decay spectrum
statistical
1.8%
Expt. systematic
2.5%
model
2.3%
1.2%
1.0%
Total SL width
3.0%
DGE theory
2.9%
WA missing here
HQL06 Munich, Germany E. Won, Korea University

12. HQL06 Munich, Germany E. Won, Korea University
+ weighted in
BaBar PRL (2006)
Instead of
assume ad-hoc model for SF and
get model parameters from bc and Bsg
Directly use measured photon energy spectrum in b sg (LLR approach)
residual SF dependence via signal MC
BaBar
(82/fb)
: partial decay rate of
: interferences btw EM penguin O7 w/ O2 and O8
: weights from in
Choose :
 Total error is minimal
Theory uncertainties
BaBar
Experimental uncertainties
HQL06 Munich, Germany E. Won, Korea University

13. HQL06 Munich, Germany E. Won, Korea University
with large acceptance
BaBar PRL (2006)
OPE allows to extract with ~ 5% error
measure entire spectrum up to 2.5 GeV
This gives acceptance ~ 97%
BaBar
(82/fb)
No shape function in extraction of
Residual SF dependence via signal MC
systematic: 5.0%
Need to subtract bc background
systematic: 3.8%
increased statistical uncertainty
Improvement in theory uncertainty
HQL06 Munich, Germany E. Won, Korea University

14. HQL06 Munich, Germany E. Won, Korea University
Exclusive decays to
measure exclusive final states
good suppression of bc decays, high signal-to-background
small branching fraction O(10-4)  need high statistics
require unknown form factor to extract
(complication due to QCD) u
need to measure q2 i.e. either 4-momentum of v or B
Channel is the most promising for
- one dominant form factor
- q2 shape and normalization needed
HQL06 Munich, Germany E. Won, Korea University

15. HQL06 Munich, Germany E. Won, Korea University
Determining the Form Factors
Earlier predictions made with quark models e.g. ISGW2
Lattice QCD
makes predictions at high q2 (q2 > ~ 16 GeV2)
unquenched calculations have become available recently
e.g. HPQCD PRD 73, (2006)
FNAL NP Proc. Suppl. 140, 461 (2005)
Light Cone Sum Rules (LCSR)
makes predictions at low q2 (q2 < ~ 14 GeV2)
e.g. Ball & Zwicky PRD (2005), PRD 71, (2005)
Parameterization has been used to extend Lattice QCD or LCSR to full q2 range
The normalization of FF becomes main issue when extracting
HQL06 Munich, Germany E. Won, Korea University

16. HQL06 Munich, Germany E. Won, Korea University
Range of Applicability of Method
Luminosity fb-1
Untagged
tag
Full reconstruction tag
Not an absolute but illustrative statement
Full reconstruction tag will become method of choice soon
Note:
Belle fb-1
BaBar fb-1 (now reached 1/ab for combined data)
HQL06 Munich, Germany E. Won, Korea University

17. HQL06 Munich, Germany E. Won, Korea University
CLEO PRD (2003)
CLEO untagged
FF models enter extraction of BF through
signal efficiency from MC
bu crossfeed and bc
CLEO
result
(p and r mode combined)
LCSR+LQCD
stat
syst
theory
FF shape
HQL06 Munich, Germany E. Won, Korea University

18. HQL06 Munich, Germany E. Won, Korea University
BaBar hep-ex/
BaBar untagged
preliminary
Updated from the last pub (PRD )
: now 227 BB pairs used
use much looser n reconstruction to improve signal efficiency
no harsh cut on |m2miss/Emiss|
calculate q2 from B momentum in “average” B-frame + unfolding
 q2 resolution still good (~400 MeV)
more parameters for background
 reduced systematics
5 times the signal yield: 25/fb-1
12 bins in q2
HQL06 Munich, Germany E. Won, Korea University

19. HQL06 Munich, Germany E. Won, Korea University
BaBar untagged
BaBar hep-ex/
preliminary
ISGW2 is incompatible with the data
LQCD & LCSR consistent with BaBar data
Covariance matrices are included in preprint  theorists can use for analyses
use BK parameterization for f+(q2,a)
Stat+syst. errors
QCD calculations
41.0
60.2
12.5
10.2
FNAL
HPQCD
37.2
13.0
Ball-Zwicky
0.07
34.1
ISGW2
3.6±0.2±
>16
FNAL
4.1±0.2±
HPQCD
3.6±0.1±
(uncertainty in FFs)
<16
Ball-Zwicky q2
 LCSR
Lattice QCD
HQL06 Munich, Germany E. Won, Korea University

20. HQL06 Munich, Germany E. Won, Korea University
Belle hep-ex/060424
Submitted to PLB
Belle with tag
Ratios of decay rates are measured and found to be consistent with isospin relations
from q2>16 GeV2 region, p-, p0 combined
q2(GeV2)
FNAL
>16
3.60±0.41± (LQCD)
HPQCD
4.03±0.46± (LQCD)
This gives ~13% experimental uncertainty on
HQL06 Munich, Germany E. Won, Korea University

21. HQL06 Munich, Germany E. Won, Korea University
BaBar with had. + SL tag combined
BaBar hep-ex/
Using 215/fb of data
Need to combine 4 measurements
2 x B-flavors:
charged and neutral B
2 x tagging methods
hadronic and semileptonic
 minimize total error in each bin of q2
BaBar
preliminary
BaBar
preliminary
q2(GeV2)
Ball-Zwicky
<16
3.2±0.2±
(uncertainty in FFs)
HPQCD
>16
4.5±0.5±
FNAL
4.0±0.5±
APE
4.1±0.5±
HQL06 Munich, Germany E. Won, Korea University

22. HQL06 Munich, Germany E. Won, Korea University
Belle with full reco tag
Belle-CONF-0666
Using 497/fb of data
Reconstruct the hadronic decay of B first
Identify a lepton and search for light mesons
Extract yield from the missing mass squared distributions
 high purity signal obtained
Belle
preliminary
MM2
Missing Mass2
MM2
MM2
Belle
preliminary
MM2
HQL06 Munich, Germany E. Won, Korea University

23. HQL06 Munich, Germany E. Won, Korea University
Summary of Exclusive
HFAG ICHEP 2006
Average
Note: updated Belle SL tag result now included
Untagged analyses currently the most precise
HQL06 Munich, Germany E. Won, Korea University

24. HQL06 Munich, Germany E. Won, Korea University
Summary of from Exclusive Decays
HFAG ICHEP 2006 (+ my bars for clarity)
LCSR
Lattice QCD
Using FF calculated in region of applicability
Using FF extrapolated to full q2 range
HQL06 Munich, Germany E. Won, Korea University

25. HQL06 Munich, Germany E. Won, Korea University
Summary
Inclusive measurements |Vub| ~ 7 % precision
shape function is one of main issues
Error is more or less equally shared by exp. and theory
BaBar’s new result (LLR) looks promising
- has residual SF dependence
Exclusive measurements |Vub| > 10 %
Form factor calculation is the main issue
Theoretical uncertainty is dominant
Question: |Vub| <5 % error achievable?
HQL06 Munich, Germany E. Won, Korea University

26. HQL06 Munich, Germany E. Won, Korea University
CLEO PRD (2003)
CLEO untagged
Search and fit for yields across a number of exclusive modes
CLEO
Isospin constraints imposed in fits on 9.7 x 106 BB pairs
Extract partial branching fraction in 3 q2 bins for and
result
HQL06 Munich, Germany E. Won, Korea University

27. HQL06 Munich, Germany E. Won, Korea University
Belle hep-ex/060424
Submitted to PLB
Belle with tag
Using 253/fb (275 million BB events)
Reconstruct tag side first
Identify leptons
Look for p or r in the remaining particles
Select events using
kinematical variables
p-ln
r-ln
Xuln
BB bkg
Extract the signal in (x2B,mX) plane with 4 signal and 3 bkg components
HQL06 Munich, Germany E. Won, Korea University

28. HQL06 Munich, Germany E. Won, Korea University
: inclusive vs exclusive
HFAG ICHEP 2006
inclusive
exclusive
HQL06 Munich, Germany E. Won, Korea University

29. HQL06 Munich, Germany E. Won, Korea University
: direct vs. indirect
Indirect measurements constrain |Vub|
 indicated as bands in the plot
inclusive
exclusive
There are two direct measurements
+: exclusive *:inclusive
The present value of sin2f1 is more compatible with exclusive determination of |Vub|
HQL06 Munich, Germany E. Won, Korea University