1. Semileptonic decay of D0  l and form factors
for the measurement of |Vub| at KEKB
Motivation, Method and preliminary results
G.Leder, J.MacNaughton, F.Mandl and L.Widhalm
Institute of High Energy Physics, Austrian Academy of Sciences
Nikolsdorfer Gasse 18, A-1050 Vienna, Austria, Europe
(BELLE Collaboration)
Abstract
When using the semileptonic decay B  l for a determination of |Vub| a form factor fB(q2) is needed. A corresponding form factor fD(q2) is measured in D0  l, since fB(q2) / fD(q2) has a smaller theoretical error. The analysis is based on about 152 fb-1 of data collected by BELLE at the e+e- assymetric collider KEKB. To get a significant number of D0  l decays events of the type e+eD(*)D(*) + i / K, i=0-5 are selected. Using a special tagging about 100 exclusive D0  l decays are obtained. Preliminary distributions fD(q2) are presented as well for the decay channel above as for D0  Klnu (the latter with about tenfold statistics). The aim of l < 10% is shown to be within reach even with currently available data. Several inclusive decays of the D0 can also be studied in view of the considerable number of D0’s.

2. Measurement of Vub via the decay B  pln
one has to use a form factor fB(q2)
an analogous form factor fD(q2)
can be measured in the decay
D  pln
the ratio fB / fD is well known by
numerical methods (lattice)

3. Method of Reconstruction
Additional
primary Mesons
3.5 GeV e+ e-
8 GeV p K
recoil D* D*
recoil p p
Mass- / Vertex Fit D
„Inverse“ Fit D
recoil
e/µ p n K p p p

4. Method of Reconstruction
There are more tasks which can be tackled by the
Method of Reconstruction
semileptonic form factors
f+D (q²) for D  pln, ambitious aim: error < 10%
may be used to reduce systematic error on f+B (q²) for |Vub| measurement
high resolution q² distribution for D  Kln
cross sections for D*D*(n p/K/p)
various channels: D*D*p, D*D*pp, D*D*KK, D*D*ppp, D*D*pppp, D*D*KKpp, ...., D*D*pp, ….
inclusive D decays BR
various channels, mostly poorly measured:
D  f, K*, , K±, e±, ± anything
Particle searches in
D*, D*K, D*p, etc.

5. Channels used for Reconstruction
D*+D*-, D*0D*0 (plus additional primary mesons)
mixed charged D*D* pairs ( i.e. D*0D*± )
D+, D- on tag side
D*0  D0, D00 on tag side
Current Statistics of D  mln , no bkg subtracted)
reconstructed neutrino mass
meson
lepton K p e
380 80
440 60
all
820
140
REAL DATA
Kln
mn² / GeV²
pln
mn² / GeV²
F.Mandl

6. Background Studies (work in progress) K/pln Analysis
Sources background for D  K/pln:
non-D events with fake D
hadronic D decays with fake lepton
fake kaon/pion in decay
reconstructed neutrino mass
REAL DATA
MC DATA
D  pln
D  Kln
non-D bkg
D  hadronic
Branching Ratio l, Kl :
compatible with PDG
mn² / GeV²

7. K/pln Analysis pln Analysis: q² distribution all preliminary Kln pln
very good q² resolution (~0.01 GeV²)
small variation of resolution with q² between and GeV²
bin width limited by statistics to much larger values (0.100 (K) (p))
therefore no unfolding necessary
MC DATA
q² resolution
REAL DATA
raw q² distribution
Kln
q² / GeV²
q²true -q²rec. / GeV²
pln
all preliminary
q² / GeV²

8. K/pln Analysis pln Analysis: q² distribution all preliminary Kln pln
shapes of bkg derived from MC except for non-D bkg (from D* side-band data)
bkg subtracted according to bkg measurement presented before
efficiency correction slightly rising with q² for K, rather flat for p
q² signal & background
Kln
REAL DATA
D  pln
non-D bkg
MC DATA
D  Kln
form factor f+(q²)
single-pole model
arbitrary normalization
REAL DATA
D  hadronic
pln
Kln
q² / GeV²
all preliminary
q² / GeV²
next step will be extraction of form factor f+(q²)
following BUTLER (Phys.Rev. D52, 2656), sf(q²) ~ spln (needs to be checked)
our advantage: comparatively clean, high resolution sample
pln
q² / GeV²

9. Inclusive decay D0  K* (892) X
(not in PDG list)
K-+ effective masses of combinations of charged particles from kinematically selected D0 via recoil, tagging only D*+D*-, D*+D*-0 and D*+D*-+- events
D0  K-+
D0  K*(892)X
Preliminary fit:
3 Gaussians
3rd order polynomial
reflection of
D0  K-+0
M(K+-)

10. Conclusion Plan statistics of ~100 D  pln (@152fb-1)
have already been reached
aim of spln<10% within reach even with currently available data
very good statistics (~28k) available for inclusive D decays
Plan
study systematics of form factor measurement
further background studies