1. e+e−→ open charm via ISR X(4160) in J/ recoil
Galina Pakhlova
ITEP
for the Belle Collaboration
Quarkonium Working Group, October 20, 2007

2. Experiment Belle
“An unexpected bonus from the B-factory experiments has been
the discovery of a large number of charmonium-like meson states…”
23/02/2019
Galina Pakhlova

3. e+e− open charm final states

4. R-study around open charm threshold
PDG 2006
e+e- machines at s ~(3.7 -5) GeV
inclusive e+e-  hadrons cross-section
complicated structure
model and fit dependent description
For years no exclusive studies e+e-  specific final states
Last years new interest both in experiment and theory
A lot of new data!!!
23/02/2019
Galina Pakhlova

5. Exclusive e+e−D(*)D* cross-sections via ISR
s=(Ecm-E)2-p2 D 
reconstructed
not reconstructed
but constrained
Method
ISR at B-factories comparable with energy scan (CLEOc, BES)
Hard ISR photon takes away significant fraction of energy
Continuous ISR spectrum: access to whole s interval
em suppression, but ~ 700/fb at Belle vs ~ 60/pb CLEO-c
The first measurement
Belle: D*+D*-, D+ D*- with partial reconstruction
increase eff ~ 10 − 20 times
23/02/2019
Galina Pakhlova

6. e+e-D(*)D* with partial reconstruction
Phys. Rev. Lett. 98, (2007)
D*+D*-
D+ D*-
Mrec(D*+ISR)
Mrec(D+ISR)
ΔMrec
Full reconstruction D(*) ISR
wide peak in Mrec(D(*)ISR) at M D*
contribution from e+e-D(*)D* (n)πγ
Full reconstruction D(*) ISR + slow from unreconstructed D*
wide peak in Mrec(D(*)-ISR) at MD
Use recoil mass difference
ΔMrec = Mrec(D(*)ISR) - Mrec(D(*)ISR)
narrow peak at (MD* - MD)
cancellation of momentum smearing
Tight ΔMrec cut  small background
Use kinematical constraint Mrecoil(D(*) ISR)  MD* to improve resolution
MD*
MD*
with ΔMrec cut
RMD~1 MeV
23/02/2019
Galina Pakhlova

7. Exclusive e+e–D(*)D* cross-sections
550/fb
(4040)
(4415)
Phys. Rev. Lett. 98, (2007)
(4160)
Y(4260)
DD*
D*D*
PRELIMINARY
(4160)
Y(4260)
(4040)
CHARM 2007
Charged D(*)D*
½ from CLEOc
Systematic errors ≈ statistical errors
Submitted to Durham database
Y(4260) signal
DD* : hint, but not significant
D*D* : clear dip (similar to inclusive R)
23/02/2019
Galina Pakhlova

8. e+e−  DD at s~3.7−5 GeV via ISR
NEW
D0D0 or D+D– (full reconstruction)
no extra tracks
670 fb-1
Combinatorial bgs are estimated from D s/b
Other bgs are small and taken into account
D+D–
D0D0
detection of ISR is not required
if ISR is detected
M(DD ISR) is required ~ Ecm
ISR is not detected
Consistent with ISR production DD
ISR is detected
23/02/2019
Galina Pakhlova

9. Mass spectra of DD Belle&BaBar are in a qualitative agreement
arXiv:
(4160)
(3770)
(4040)
(4415)
Y(4260)
670 fb-1
arXiv:
(4415)
(4160)
(4040)
Y(4260)
384 fb-1
no signal Y(4260)DD
Belle&BaBar are in a qualitative agreement
23/02/2019
Galina Pakhlova

10. (e+e–  DD) DD Charm 2007 D*D* DD* Broad structure around 3.9 GeV
(4040)
(4160)
(4415)
670 fb-1
(3770)
(e+e–  DD)
(4040)
(4160) DD
PRELIMINARY
Charm 2007
D*D*
DD*
Phys. Rev. Lett. 98, (2007)
Broad structure around 3.9 GeV
is in qualitative agreement ??
with coupled-channel model
Phys. Rev. D21, 203 (1980)
Cross section above 4 GeV
has a similar shape to this
measured for ee  D*D* ?
σ(ee  D+D−)/σ(ee  D0D0) = 0.720.160.06
at MDD≈M(3770)
is consistent with BES/CLEOc
23/02/2019
Galina Pakhlova

11. e+e−  D0D–+ at s ~ 4−5 GeV via ISR
NEW
e+e−  D0D–+ at s ~ 4−5 GeV via ISR
Consistent with ISR production
670 fb-1
D0 D− +
full reconstruction
no extra tracks
similar analysis and bgs
no major bgs except for combinatorial
Clear (4415)DD signal
23/02/2019
Galina Pakhlova

12. Resonant structure in (4415)DD
M(D0+) vs M(D-+) from (4415) region
Clear D*2(2460) signals
Positive interference
Non D*2(2460) contribution is not seen
DD non DD*2(2460)
DD*2(2460)
~10σ
670 fb-1
arXiv: , submitted to PRL
M = 4411± 7 MeV
tot =77±20 MeV
Nev= 109± 25
Consistent with BES,
hep-ex/ ,
PDG06, Barnes at.al
Phys. Rev. D72, (2005)
σ(e+e-(4415))×Br((4415)DD*2(2460))×Br(D*2(2460) D)=(0.74±0.17±0.07)nb
Br((4415)  D(D)non D2(2460))/Br((4415) DD*2(2460))<0.22
23/02/2019
Galina Pakhlova

13. Contributions to the inclusive cross-section at 3.7-5GeV
D*D*
DD*
Phys. Rev. Lett. 98, (2007) DD
NEW
arXiv:
submitted to PRD(RC) 2 + +
DDπ
NEW
arXiv: , submitted to PRL = 2
uds-continuum
Anything else?
These 4 final states almost
saturate inclusive cross section
23/02/2019
Galina Pakhlova

14. New state in double charmonium production

15. New study of e+e−  J/ D(*)D(*)
693fb-1 D*
D*π D
arXiv:
All signals are > 5
The method is pioneered by Belle
Reconstruct J/ and one of
two D (or D*)
Unreconstructed D(*) is seen
as a peak Mrecoil (J/ D(*))
D and D* recoiling against reconstructed J/ D(*) are well separated (~2.5)
Simultaneous fit to D-signal
and D-sidebands to fix bg
Phys. Rev. Lett. 98, (2007)
23/02/2019
Galina Pakhlova

16. e+e–J/DD D D 3.8  Tag unreconstructed D:
|Mrecoil (J/ D) - M D | < 70MeV
Refit Mrecoil (J/ D) M D :
improve M DD by ~10
Broad peak at MDD is not consistent with non resonant
DD production in the process
e+e−  J/ DD
large fitting systematic error in the parameters of this enhancement
23/02/2019
Galina Pakhlova

17. D*-reconstructed D-tag
e+e– J/DD* and D*D D*
X(3940)
D reconstructed D*tag
6.0 
ee  J/ DD reflection
M = ±6 MeV
tot = ±12 MeV
Nev= ±11 +7 -6
+26
- 15
+24
- 16 D
D*-reconstructed D-tag
X(3940)
cross check
3.8 
X(3940)DD* confirmed with new data
M and  are in agreement with published results.
23/02/2019
Galina Pakhlova

18. D*reconstructed D*tag
e+e−  J/ D*D* D*
Broad clear peak at threshold
New state X(4160) ≠ ψ(4160) is observed in D*D* decay mode
M=( 15)MeV/c2
 =( 21)MeV
+25
−20
+111
−61
5.5 
X(4160)
D*reconstructed D*tag
One more particle to explain …
JPС=0− + (hc (4S)) is not excluded
23/02/2019
Galina Pakhlova

19. Summary

20. e+e− open charm D*D* DD* DD DD
complicated shape of cross section
consistent with CLEO_c at MD*D* ( ) GeV
clear dip at MD*D* ~ 4260GeV (similar to inclusive R)
DD*
broad peak at threshold (shifted relative to 4040 GeV)
consistent with CLEO_c at MDD* ( ) GeV
hint at MDD* ~ 4260GeV DD
consistent with CLEO_c at MDD ( ) GeV
σ(ee(3770)→DD) consistent with BES/CLEO_c
broad enhancement ~ 3.9 GeV – coupled channel effect?
above 4GeV similar shape as D*D*
DD
(4415) signal observed, dominated by (4415)  DD**2
DD + DD + D*D + D*D* cross section is close to
ee  hadrons ( - ee  uds continuum)
23/02/2019
Galina Pakhlova

21. Double charmonium production
X(3940)
is confirmed with a significance ~ 6.0
X(4160)
NEW state observed for the first time ~ 5.5 
23/02/2019
Galina Pakhlova