1. Wiener Charm-Physik bei BELLE Laurenz Widhalm HEPHY Wien
Belle in a nutshell
Absolute Formfaktoren von semileptonischen D0-Zerfällen
Absolute Formfaktoren von semileptonischen Ds-Zerfällen
Inklusive & exklusive Verzweigungsverhältnisse bei D0-Zerfällen
located at KEK / Japan
KEKB Collider
B-Factory at (4s) resonance
peak luminosity /nb/s
integrated luminosity 600 1/fb (as of June 2006; 280 1/fb used in this analysis)
main physics goal: observation of CPV in B meson Decays e-
8GeV e+
3.5GeV bg
= 0.425
Laurenz Widhalm
HEPHY Wien
Belle Collaboration
KEK 高エネルギ

2. I. Charm2006

3. Semileptonic D0 Decays q² single form factor fD(q2)
calculable in LQCD, but
needs checking from data
D-System ideal for experimental input
results can be applied in B-physics (extraction of CKM parameters)

4. Method of Reconstruction (Event Topology)
additional primary mesons  IP
3.5 GeV e+ e-
8 GeV p K
recoil n D0
pslow
e/µ-
K/p+
D*-
„inverse“ fits D* p g
mass-constrained vertex fits D p p
note:
all possible combinations tried in parallel
cuts after complete reconstruction
equal weight for remaining combinations
 no event loss due to particle exchanges!
Ktag p 
tag side
signal side 

5. result D0 Signal and Background* after cuts background signal
* from decays without a D0 , or combinatorial background
control region
signal region
same sign
Ktag/pslow
s= GeV!
signal D0 invariant mass
result
(282 fb-1 of BELLE data)
yield
after cuts
95250
background
38789
signal
charge correlation
signal subtraction
stats bkg sample
56461
± 309stat
± 776syst
± 233syst
± 194syst
opposite sign
Ktag/pslow
note: data used for bkg subtraction,
MC shown only for comparison MC
charm (D°) MC B0
data (normalized) MC
charm, no D° MC
uds MC B± MC
wrong sign D°

6. Summary of Signal / Background Decomposition
D0  Ken
remaining signal
D0  pen
data
data
fake-D0 bkg
D0  Kmn
D0  pmn
hadronic bkg
data
Kln bkg
data MC
K*/rln bkg
mn² / GeV²
Results (282 fb-1 of data)
Ken
Kmn
pen
pmn
signal events
1318
± 37stat ± 7syst
1249
± 37stat ± 25syst
126
± 12stat ± 3syst
106
± 12stat ± 6syst
fake D0 bkg
12.6 ± 2.2
12.2 ± 4.8
12.3 ± 2.2
12.5 ± 4.5
semileptonic bkg*
6.7 ± 2.6
10.0 ± 2.5
11.7 ± 1.2
12.6 ± 1.9
hadronic bkg**
11.9 ± 5.6
62.1 ± 23.9
1.8 ± 0.7
9.7 ± 3.7
* error dominated by MC statistics ** error dominated by fit errors & bias special bkg sample

7. Absolute Branching Ratios
ratio to total number of recoil D0 tags
efficiency correction
corrected for bias due to differences data/MC
(1.9%±3.9%)
BRs (%)
this analysis
PDG
(2005)
CLEO-c
(hep-ex/ )
K-e+n
3.45 ± 0.10stat ± 0.19syst
3.62 ± 0.16
3.44 ± 0.10stat ± 0.10syst
K-m+n
3.45 ± 0.10stat ± 0.21syst
3.20 ± 0.17
p-e+n
0.279 ± 0.027stat ± 0.016syst
0.311 ± 0.030
0.262 ± 0.025stat ± 0.008syst
p-m+n
0.231 ± 0.026stat ± 0.019syst
0.24 ± 0.04

8.  no unfolding necessary!
Form Factors – q² distribution
D0  Ken
D0  pen
signal q²
non-D bkg
hadronic bkg
semileptonic bkg
s(q²) = GeV²/c²
(width of red line)
 no unfolding necessary!
D0  Kmn
D0  pmn
background shapes from data

9. (poles fixed at theo. values)
Form Factors – Comparison with Models
modified pole model
D0  Kln
lattice calculation
ISGW2 model
fit results
simple pole
pole mass (GeV)
Kln
1.82 ± 0.04stat ± 0.03syst
pln
1.97 ± 0.08stat ± 0.04syst
D0  pln
modified pole
(poles fixed at theo. values)
f+(0)
Kln
0.695 ± 0.007stat ± 0.022syst
pln
0.624 ± 0.020stat ± 0.030syst a
Kln
0.52 ± 0.08stat ± 0.06syst
pln
0.10 ± 0.21stat ± 0.10syst

10. Semileptonic Ds Decays
PDG:Ds

11. ... Reconstruction Method for Ds  3.5 GeV e+ e- 8 GeV p p K g g D Ds-
additional primary particles IP 
3.5 GeV e+ e-
8 GeV
Ds*-
recoil p p K
... g
recoil g
mass-constrained vertex fits D
„inverse“ fits
Ds- p p
recoil µ- n
Ktag p 
tag side
signal side 

12. DATA (Exp7-Exp49) Ds in BELLE data
~20000 events
measurements of inclusive & exclusive channels planned
reconstruction of decay products of Ds, e.g. muon and neutrino of
Ds  mn or Ds F m n
will further reduce ambiguity
Ds invariant mass / GeV

13. inclusive & exclusive BRs of D0
KK-Spectrum for D0(KK) X
Missing Mass for D0(KK) X
M(K+K-)
M(X)
D0 F X K0
D0K+K-
D0K+K-K0
D0K+K-p0 p0
p misidentified as kaon
p misidentified as kaon

14. Summary & Outlook
events searched in e+e-  D(*)D*cX and e+e-  DDs*KX (X=np/K/g)
new full-reconstruction-recoil method
absolute D0 BRs of better accuracy than previous experiments, in good agreement with recent CLEO measurements
high q² resolution, no unfolding necessary
absolute multi-bin measurement of f+(q²)
measured form factor in good agreement with theoretical predictions and other experiments
new Ds analysis will yield inclusive BR measurements and better knowledge of Ds form factor
improvements of various inclusive and exclusive BRs of D0  (KK)X (future: (Kp)X, (pp)X)
Phys.Rev.Lett.97:061804,2006 (hep-ex/ )

15. Spares

16. Best Candidate Selection (MC check)
Ds invariant mass
Ds invariant mass
no best candidate selection
largest “slow” pion energy taken
signal / no ambiguity
signal / several associations
signal / lost because wrong candidate selected
background

17. additional primary mesons
Method of Reconstruction (Event Topology)
tag side:
reconstruction & fit of D0,±  Kp, K2p, K3p
reconstruction & fit of D*0,±  Dp, Dg
use either D or D* as primary meson
signal side:
reconstruction & fit of inclusive D*0,± via recoil from e+e-  D(*) D*np/K
reconstruction & fit of inclusive D0 via recoil from D*  Dp
reconstruction & fit of neutrino via recoil from D  mpn
additional primary mesons e+ e- p K
( ) D* D* D p g D p p p K p
e/µ p n
tag
signal

18. Method of Reconstruction (Event Topology)
D*-sig
m/GeV
m/GeV
D*+tag
D*0 tag
D0sig
m/GeV

19. List of Cuts unstable particle selection: stable particle selection:
gammas:
p > 40 MeV
charged tracks (general):
p > 100 MeV
trk_fit.nhits(3) > 0
dr < 2 cm, dz < 4 cm
electron:
p > 500 MeV
eid.prob(3,-1,5) > 0.9
muon:
prerejection != 1
Muon_likelihood > 0.9
kaon / pion:
atc_pid (3,1,5,3,2)
prob*(1-prob_e-prob_mu) > 0.5
for meson in hlnu: > 0.9
List of Cuts
unstable particle selection:
pi0:
PDG mass ± 10 MeV
fit CL > 0.1
K0:
only via decay pi+pi-
PDG mass ± 25 MeV
D_tag:
channels Knpi, n=1-3
PDG mass ± 20 MeV
D*_tag:
channel Dpi, Dg
PDG mass ± 5 MeV
mass/vertex fit CL > 0
D*_signal:
via recoil from D*_tag+n pi/K, n=0-5
mass/vertex fit CL > 0.001
D_signal:
via recoil from D*_signal  Dpi n:
via recoil from D_signal  hlnu
|m²| < 0.05 GeV²
additional Klnu / pilnu cuts:
E_leftover < 700 MeV, no leftover charge
E_nu > 100 MeV
right charges of slow pions & lepton

20. Bias by mass-constrained Fits on Background?
no real D0  
with real D0
after fit of D*
before fit of D* 
D0 invariant mass
very sharp mass peak after fit
no bias on background 

21. D0 Signal and Background*
* from decays without a D0 , or combinatorial background
cuts
confidence level of all mass-constrained vertex fits >0.1% (released on D0 fit for righthand plot)
right charge correlation between slow pion and tag side kaon (right sign, RS)
control region
same sign
Ktag/pslow
signal D0 invariant mass
procedure to measure background:
select wrong charge correlation data (WS) to get shape of background
correct for small WS signal component
normalize to RS data in region GeV
signal region
opposite sign
Ktag/pslow
charm MC
B0 MC
data (normalized)
charm, no D°
uds MC
result (282 fb-1 of BELLE data)
yield
selected D0 events
95250
subtracted background
38789
signal
56461
± 309stat ± 830syst
B± MC
wrong sign true D°
systematics breakdown
events
charge correlation RS/WS
776
WS signal subtraction
233
statistics of WS sample
194

22. Measurement of Semileptonic Background (for pln)*
procedure to measure background:
1. crosstalk from Kln:
prepare special background sample, with K intentionally misidentified as p
normalize to standard Kln sample
then reweight the sample using known** efficiencies / fake rates (in p,)
2. background from vector mesons:
get shapes for K*ln and rln from MC (simulated ratio K*/r from PDG)
normalize to data in region m²n > 0.3 GeV²
recoil neutrino mass
control region for K*/r bkg measurement
D0  pln
signal region
data
non-D° bkg (measured as described previously)
* background for Kln is very small, and is handled the same way
** measured independently in data
measured bkg from Kln
measured bkg from K*ln
measured bkg from rln

23. Measurement of Hadronic Background (for pmn)*
procedure to measure background:
prepare special background samples, with K(p) intentionally misidentified as m (subtract fake D0 background in these samples with the method described above)
separate into same sign (SS) and opposite sign (OS) samples, with respect to the charges of the lepton and the slow pion
semileptonic channels are highly suppressed in OS  clean sample of hadronic background
perform a 2-parameter fit in the standard OS sample, using the shapes from the OS background samples for K and p, to measure the effective fake rates
then apply these fake rates in the background SS sample to obtain the backgrounds in the signal sample
same sign SS
signal: D*  D0p+
 p-m+n SS
both signs
D*  D0p+
 p-p+p0/K0
p-m± n
opposite sign OS
D*  D0p+
 K-p+p0
p+m-n SS OS OS
D*  D0p+
 K-p+p0/K0
p-m+ n
* significant background only for this channel; other channels are handled likewise

24. Fit of Hadronic Background (for pmn)*
D0  pmn
comparison with MC SS
MC true composition
use result of fit here 
green = particle seen in recoil mass
D0  p-p+p0
D0  K-p+p0
D0  K0p-p+
fit in this sample  OS
signal region
bkg from misidentified kaons
bkg from Kmn
bkg from misidentified pions
bkg from K*/rmn
* background for pen and Kln are much smaller
remaining events in signal region
fake-D0 bkg

25. Form Factors - Theory    f+(q²) = 1-q²/m²
in principle, two form factors f+(q²) and f-(q²)
kinematically only f+(q²) relevant, f-(q²) suppressed by ml²
three different models that are frequently discussed in literature:
simple pole
f+(q²) = 1-q²/m² 
 f+(0)
m......pole mass
= m D*s  2.11 GeV (Kln)
= m D*  2.01 GeV (pln)
modified pole
f+ (q²) = (1-q²/m²) (1-aq²/m²)
 0.50 (Kln) 
atheor.
G. Armoros, S. Noguera,
J. Portoles,
Eur. Ph. J. C27, 243 (2003)
 0.44 (pln)
ISGW2
f+ (q²) = (1-a(q²-q²max))²
N. Isgur and D. Scora,
Phys. Lett. B 592 1(2004) 

26. Measured Absolute Form Factors as function of q²
D0  Ken
D0  pen
D0  Kmn
D0  pmn
extracted by dividing q² distribution by kinematical factor
no unfolding necessary due to very good q² resolution