1. Charm Semileptonic decays with BaBar
Alessia D’Orazio pos-doc LAL
Arantza Oyanguren IFIC Valencia
Patrick Roudeau LAL
Justine Serrano phD LAL
João Costa phD LAL

2. Charm semileptonic decays
Introduction
Several measurements need precise Lattice calculations of
hadronic effects in weak interactions (fB, Bk, ξ ... )
Large effort from Lattice community to improve computation methods
lead to a better accuracy
Need to be validated
Charm semileptonic decays
Vcs, Vcd
Measurement
of form factors
Techniques validated in the charm sector can then be used
in the B sector to improve the accuracy on CKM parameters
determination

3. Charm Semileptonic Decays also provide other important informations:
ex: phase shifts between different orbital states in 4-body sl. decays (Dl4)
ex: mass of the hadronic system in 4-body sl. decays (Dl4):
DKπlν, DsKKlν, (in particular, 0+ states)
J/K*(892)0 K+-
(BES, hep-ex/ )
ex: determination of chiral theory parameters, determination of the strange quark mass

4. future! future! future! future! We want to: finished! in progress!
Measure the q2 variation of
various form factors entering in
Cabibbo allowed & supressed
semileptonic decays
finishing!
future!
in progress!
Measure channels with two hadrons
in the final state, in order to study
low mass K-π, K-K & π-π systems,
in particular from S-waves
future!
future!
Perform correponding measurements
of charmed baryons for semileptonic
decays ( only produced at B-factories)
future!

5. Charm Production at BaBar
Large cross section
Large integrated luminosity
cc ~1.3 nb
Large data sample available at Babar
400 fb-1
(typically 0.5M evts with BR=1%, ε =10%)
fragmentation (D, Ds,Λc,…)
main challenge : background control

6. Analysis method Analysis basis: - Untagged analyses:bb - cc
Untagged analyses:
 large statistics
 some background
From continuum events
 use event shape variables to remove BB’s
 use event topology and kinematical
variables to reduce the charm background
Kinematical fit to extract the q2=(pl+pn)2= (pXc-pXq)2
 input missing energy in the event and D direction estimates
Different fit methods to extract the form factor(s)
Data control samples: test the efficiency reconstruction,
resolution, control on systematics ...

7. after the fit with 2 constraints: mD* and mD
Decay characterisics
● DKen:
Mass difference distribution
q2 distribution
Peaking cc =46%
Non-peaking cc= 31%
BB= 21%
75 fb-1
q2 =(pD-pK)2
after the fit with 2 constraints: mD* and mD
dm (GeV/c2)
dm =m(K-l+np+)-m(K-l+n) after the fit with 1 constraint on mD
85000 events (13% bkg)

8. Results experiment stat mpole(GeV/c2) αpole ● DKen: preliminary
CLEO-c
281 pb-1
1.97±0.02±0.01
0.21±0.04±0.03
FOCUS
13k evts
1.93±0.05±0.03
0.28±0.08±0.07
Belle
282 fb-1
1.82±0.04±0.03
0.52±0.08±0.06
BaBar
75 fb-1
1.884±0.012±0.015
0.38±0.02±0.03
preliminary
PRL94 (05)
PRL97 (06)
arXiv:
 same accuracy as CLEO-c
 Pole mass below mD*s (=2.112 GeV), we exclude the simple pole mass model
 α measurement lower than lattice QCD value: α =0.50  0.04
PRL94 (05)
Disagreement between values from BaBar and CLEO-c  has to be clarified !

9. ● DKen: Similar distributions for f+(q2) between BaBar and Cleo-c
Disagreement non noticiable if regarding this plot

10. Results (Relative to D  Kp) ● DKen: Other models:
ISGW2
aI= ± ± GeV-2
Disagreement with predicted value
We exclude this model
aI= GeV-2
a1/a0 = -2.5 ± 0.2 ± 0.2
t  q2
Taylor expansion
a2/a0 = 2 ± 6 ± 4
 One parameter is enough to describe the FF shape
(Relative to D  Kp)
Branching fraction:
= (3.522 ± ± 0.045±0.065 )%
Lattice: f+(0)= 0.73 ± 0.03 ± 0.07

11. phD of Justine Serrano ● Dseν: Preliminary results
 75 fb-1 (1/5 of the total data)
   K+K- reconstruction
(no  reconstruction from Ds*Ds)
● Data  signal  BB  cc peaking  cc non-peaking  uds
 26% of background (13000 signal evts)
 The Ds en decay rate depends on
4 variables: q2,  v , l ,  and 2 form factor
ratios rv and r2
A1(q2), A2(q2), and V(q2) shapes:
 Pole form factors
 More sophisticated (B&K based) 
Fajfer and Kamenic, PRD72(05)

12. Preliminary results ● Dseν: phD of Justine Serrano
● Data  fit result
 BB  cc
 uds
● Data  fit result
 BB  cc
 uds
 Fit in 4D, using pole form
factor shapes:
with MA=2.5GeV and
MV =2.1 GeV
r2 = ± ± 0.029
rV = ± ± 0.038
hep-ex/
phD of Justine Serrano

13. r2 rv Soon: Determine A1(0) Publish a paper ● Dseν:
Preliminary results r2 rv
 Similar accuracy as D K*ln
 Letting free the axial pole mass in the fit :
r2 = ± ± 0.096
rV = ± ± 0.068
MA= ± GeV/c2
+0.54
-0.34
Soon:
Determine A1(0)
Publish a paper
phD of Justine Serrano

14. Measurement of form factors according to BK model
● Dπen:
 230 fb-1 (1/2 of the total data)
 60 % of background(~10000 signal events)
Measurement of form factors
according to BK model

15. Results expected soon with very competitive precision in α,
● Dπen:
Competition
0.37
Δα=0.05 (stat)
we expect to control systematics up to the same level as the stat. errors
Results expected soon with very competitive precision in α,
B pln
~17% of
B→ pln evts
dΓ/dw
D pln w
We also want to exploit the relation:
w overlap to relate D and B form factors ( lattice people this information concerns you!)

16. { q2, cos(θv= θK) , cos(θl) , χ, mKπ }
● DKπen:
4 body decay → 5 variables
{ q2, cos(θv= θK) , cos(θl) , χ, mKπ }
Channel dominated by K*0 ( JP = 1- ) decay mode
3 form factors (A1,A2,V)→(H+,H-,H0)
B0-B0bar
B+B-
uds
We can measure the form factors
for the K*0(892),
study the S-wave and try to give
some limits for the D-wave
bkg cc

17. ● DKπen:
Now we are measuring the phase shift variation between S-P waves with mKπ
Last measurement comes from LASS
BABAR
FOCUS
generic MC signal
generic MC
data (bkg subtracted)
+ data
~14k signal events
CLEO-C has 2.5k events
 347 fb-1
 33 % of background(~200k signal events)

18. F1= F1seiφs + F1peiφpcos(θK) F2= F2peiφp F3= F3peiφp
● DKπen:
Analysis done using PW
expansion
F1= F1seiφs + F1peiφpcos(θK)
F2= F2peiφp
F3= F3peiφp
(F1P,F2P,F3P)↔(H+,H-,H0)

19. To extract the phase shift we follow Pais & Treiman:
Interference terms
Each Ii term has a different combination of angular variables dependence, they are orthogonal states
To extract the phase shift we follow Pais & Treiman:
Only one of these moments is non-zero
for each one of these integrations

20. PRELIMINARY results for F1F2
● DKπen:
PRELIMINARY results for F1F2
Sin(δs – δp)
Cos(δs – δp)
K*0(892) pole
K*0(892) pole
More tests needed
More tests needed
green dots represent result with 120% bkg
blue dots represent results with 80% bkg

21. Conclusion
Charm Semileptonic decays are an important testing ground for LQCD
They also provide results for observables used in low energy effective theories
We have results for the form factors of :
and expect results soon for :
Measurement more precise than Lattice
Much more precise than previous experiments
And there are still lots of interesting things to be done..