1. Rare and forbidden charm decays
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
Rare and forbidden charm decays
Boštjan Golob
University of Ljubljana/Jožef Stefan Institute & Belle/Belle II Collaboration
Introduction
D10 → D0g
D0 → l+ l-
University
of Ljubljana
“Jožef Stefan”
Institute
Charm 2010, IHEP, Beijing, Oct 21 – 24, 2010

2. Introduction Experiments B-Factories BaBar @ PEPII SLAC Belle @ KEKB
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
Introduction
Experiments
B-Factories
PEPII
SLAC
KEKB
KEK
on resonance production
e+e- → U(4S) → B0B0, B+B-
s(BB)  1.1 nb (~109 BB pairs)
s(c c)  1.3 nb (~1.3x109 XcYc pairs)
Nrec(D*+ → D0 p+ → K- p+ p+)  2.5x106
continuum production g* c
B-factory=
charm factory
Belle Ldt  1020 fb-1
BaBar Ldt  550 fb-1

3. 1P → 1S radiative transition L=1 D mesons:
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
D10 → D0g M
[GeV]
D00 D1’ D10 D20
Motivation
1P → 1S radiative transition
L=1 D mesons:
broad (j=1/2) doublet
D00 → Dp, D1’0 → D*p
S-wave decays
narrow (j=3/2) doublet D10, D20
D-wave decays
L=1 Ds mesons:
“broad” doublet
Ds0+ → DK, Ds1’+ → D*K
narrow doublet Ds1+, Ds2+
exotic 4q states / convetional qq with
corrections to q model/HQL ?
2.75
2.25
1.75   
L=1
D mesons,
D** 
D*p Dp
j=1/2
j=3/2 JP M
[GeV]
Ds0+ Ds1’ + Ds1+ Ds2+
2.6
2.4
2.2  
D*K
L=1
Ds mesons,
Ds**  DK 
j=1/2
j=3/2 JP

4. 1P → 1S radiative transition
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
D10 → D0g M
[GeV]
D00 D1’ D10 D20
Motivation
1P → 1S radiative transition
use (not measured yet)
D** radiative transitions as
probes of internal structure;
test the HQL, mixing between
1+ states;
obvious 1st choice:
D10 → gD0 (p0D0 forbidden)
2.75
2.25
1.75   
L=1
D mesons,
D**  Dg JP
S. Godfrey, PRD72, (2005)

5. D10 → D0g Method D** from B decays B- →D10p - → (D0g)p - → (K-p+g) p -
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
D10 → D0g B- p- DJ
g, p0 D0 qJ
Method
D** from B decays
B- →D10p - → (D0g)p - → (K-p+g) p -
background from B- →D**0p - → (D0p0)p -
(D00/D20)
different helicity angle;
simultaneous fit in bins of cosqJ:
M(D0p0) for B- → (D0p0)p - decays;
MC: feed-down shape & relative e
for D0p0 reconstr. as D0g
MC using results on D00/D20 properties
from
Belle, 605 fb-1, preliminary
bins used in the
measurement
cosqJ
B- → (D0p0)p -
-1<cosqJ<-0.7
Belle, PRD69, (2004) 60 fb-1
M(D0p0)

6. D10 → D0g Method D** from B decays B- →D10p - → (D0g)p - → (K-p+g) p -
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
D10 → D0g
Method
D** from B decays
B- →D10p - → (D0g)p - → (K-p+g) p -
simultaneous fit in bins of cosqJ:
M(D0g) for B- → (D0g)p - decays;
feed-down from D0p0 fixed
Belle, 605 fb-1, preliminary
-1<cosqJ <-0.7
-0.7<cosqJ <-0.4
-0.4<cosqJ <0
0<cosqJ <0.4
sum
signal
feed-down
M(D0g)

7. D10 → D0g Result (first observation)
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
D10 → D0g
Result (first observation)
using B(B- → D10p -)=(1.5±0.6) ∙10-3
from PDG 
Belle, 605 fb-1, preliminary
sum over cosqJ bins
sum
signal
feed-down
Ns=104 ±15
M(D0g)
S. Godfrey, PRD72, (2005)

8. FCNC of uplike (c) quarks;  complementary constraints to B
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
D0 → l +l -
Motivation
FCNC of D mesons
FCNC of uplike (c) quarks;
 complementary
constraints to B
(and K) rare decays;
NP: enhancement of
B(D0 →m+m-), B(D0 →e+e-),
by orders of magnitude;
possibility of LFVB(D0 →e+m-);
example R SUSY:
B(D0 →m+m-)~4∙10-6
B(D0 →e+e-)~10-10
B(D0 →e+m-)~10-6
short distance, B~10-18
long distance, B~few 10-13
G. Burdman et al., PRD66, (2002)

9. M(ll ), q=M(ll ps)-M(ll )-mp , Emiss ,
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
D0 → l +l -
Method
Normalization D0 →p+p -
tagged D*+ →D0ps-;
blind optimization of
M(ll ), q=M(ll ps)-M(ll )-mp , Emiss ,
F.O.M.= ell /NUL
comb. backgr. from q sideband,
linear in M, q;
D0 →p+p - control sample:
same kinematic selection (except M);
normalization;
misid. background (p → m), using
measured misid. probabilities w(p,cos q)
Belle, PRD81, (2010), 660 fb-1
sideband
signal
region
excluded
sideband
Npp 
50·103

10. D0 → l +l - Results D0 →l +l - yield
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
D0 → l +l -
signal
window
Results
D0 →l +l - yield
U.L.’s calculated from N and Nbgexp
including systematic uncertainties
(negligible)
90% C.L.
Belle, PRD81, (2010), 660 fb-1
channel
D0 →mm
D0 →ee
D0 →em N 2 3
Nbgexp
3.1±0.1
1.7±0.2
2.6±0.2
90% C.L. U.L.;
comb. backg.;
D0 →p+p - backg.;
observed;
acc. to PRD(RC)

11. D0 → l +l - Results Constraints on NP l R SUSY:
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
D0 → l +l -
Results
Constraints on NP
R SUSY:
constraints on R couplings;
leptoquarks:
(genuine, coupling to l q;
contribute to D(s) → mn, D0 → mm)
B(D0 → mm)<1.4 ∙10-7
B(Ds → mn)=(0.590 ±0.033)%
fDs(LQCD)=(248.0±2.5) MeV c u l
J. Kamenik, private comm.
G. Burdman et al., PRD66, (2002)
1.5
1.0
Ds → mn
0.5
KL → mm
allowed
0.0
D → mn
I. Dorsner et al., PLB682, 67 (2009)
-0.5
-1.0
-1.5
x10-4
parametrization of
leptoquark couplings

12. D0 → l +l - Results Constraints on NP l R SUSY:
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
D0 → l +l -
Results
Constraints on NP
R SUSY:
constraints on R couplings;
leptoquarks:
(genuine, coupling to l q;
contribute to D(s) → mn, D0 → mm)
B(D0 → mm)<1.4 ∙10-7
B(Ds → mn)=(0.590 ±0.033)%
fDs(LQCD)=(248.0±2.5) MeV c u l
J. Kamenik, private comm.
G. Burdman et al., PRD66, (2002)
1.5
1.0
D0 → mm
Ds → mn
0.5
KL → mm
allowed
0.0
D → mn
I. Dorsner et al., PLB682, 67 (2009)
-0.5
-1.0
-1.5
x10-4
parametrization of
leptoquark couplings

13. B-factories active also in rare charm decays
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
Summary
B-factories active also in rare charm decays
1P → 1S charm meson radiative transition
measured for the first time
best UL’s on D0 →l +l -
FCNC of charm:
complementary constraints to rare B decays

14. Additional information
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
Additional information
D** from B decays
B- →D10p - → (D0g)p -
→ (K-p+g) p -
background from
B- →D**0p - → (D0p0)p -
(D00/D20)
different helicity angle;
simultaneous fit in bins
of cosqJ:
M(D0p0) for B- → (D0p0)p -
decays

15. Additional information
D10 → D0g motivation
D0 → l+ l- motivation
D10 → D0g method
D0 → l+ l- method
D10 → D0g results
D0 → l+ l- results
Additional information
Normalization D0 →p+p -
tagged D*+ →D0ps-;
D0 →p+p - control sample
F.O.M.= ell /NUL
background estimated
from tuned MC (6x data)
UL’s
FC w/o syst.
2.97