Institute of High Energy Physics, CAS
Surprises from charmonium decays
Qiang Zhao
Institute of High Energy Physics, CAS
and Theoretical Physics Center for Science Facilities (TPCSF),
CAS
zhaoq@ihep.ac.cn
第九届全国重味物理和CP破坏研讨会，2011年10月12-16日，杭州
Outline
1. Charmonium and charmonium-like states
2. Direct evidence for open charm threshold
effects in e+e-  J/, J/ 0, and c
3. Puzzles in charmonium decays
4. Summary
• Recent experimental progress
New charmonium-like states, i.e. X, Y, Z’s, are
observed in experiment
• Do not fit in the conventional charmonium spectrum as
quark-antiquark states.
• Most of these new states, such as X(3872), are located
close to a two-particle threshold.
• Evidence for charged charmonium states, e.g. Z(4430).
• Good candidates for hadronic molecules or other nonstandard configurations, e.g. tetraquarks, hybrids, etc.
• Greatly enrich our knowledge about strong QCD.
Charged charmonium
spectrum
-- A completely new
scenario of strong QCD!
States close to open
thresholds
-- The role played by
open D meson channels?
Close to DD* threshold
S=0,1
c
L
c
J=L+S
1010.5827
[hep-ph]
Observation of X(3872)
new Belle meas.
<MX>= 3871.46 ± 0.19 MeV
new CDF meas.
MD0 + MD*0
3871.8±0.4 MeV
dm = 0.35 ± 0.41 MeV
• The mass of X(3872) does not fit in (cc) 1++ state of quark model
• Small mass difference to DD* threshold
• Large isospin-violating decay modes
• JPC = 2 is not ruled out
Nature of X(3872)
• A good candidate for hadronic molecule
(Tornqvist 1991)
BX = 0.35 ± 0.41 MeV
• The compositeness criterion can be applied
• Tremendous contributions from theory commu.
A
B
C
.
.
.
Z
Proton
u
d
u

d
d
Neutron
u
Deuteron: p-n molecule
Charged charmonium-like states
S.K. Choi et al., PRL 100,142001 (2008)
• Resonant structure
Z(4430)
–
–
–
–
Close to D*D01 threshold
Q = 1, JP= 0,1,2
M= 4433 MeV
= 45 MeV
First direct evidence for an
exotic quark configuration,
i.e. (cc ud).
arXiv:1105.4583[hep-ex]
Look for direct evidence for open
charm threshold effects:
1) Spectrum studies
2) Production and decay processes (e.g.
e+e-  J/, J/ 0, c )
1010.5827[hep-ph]
X(3900)
Close to DD* threshold
i) Charmonium production in ee    final particles
*
1,
…
e
Belle, BaBar, and BEPC-II
……
e+
• Direct production of
vector charmonium states
• Dynamics for
charmonium interactions
with final states
• Signals for exotics?
X(3900)?
• Open charm effects in the cross section lineshape studies
e+e-  DD
• What is X(3900)?
• Not inlcuded in
PDG2010.
• Not in charmonium
spectrum
•……
Pakhlova et al., Belle
Colla., PRD77,
011103(2008).
Y.-J. Zhang and Q. Zhao,
PRD81, 034011 (2010)
e+e-  DD
e+e-  DD* + c.c.
DD* open threshold may explain:
Y.J. Zhang and QZ, PRD81, 034011 (2010)
ii) Direct evidence for open charm effects in ee  J/ , J/ 0
(3770)
J/ (I=0)
D0
(3770)
(I=0)
D
D0
 (I=0)
0 (I=1)
(b)
(a)
J/ (I=0)
D*
D*0
 (I=0)
0 (I=1)
For the isospin-violating J/0 production:
If mu = md ,
 m(D0) = m(D)
(a) + (b) = 0
If mu  md,
 m(D0)  m(D)
(a) + (b)  0
• Cross section lineshape of
e+e  J/ 
• Direct evidence for open charm effects in the cross section
lineshape of e+e  J/ 0
~ 8 MeV
Wang, Liu, Zhao, 1103.1095[hep-ph], PRD84, 014007(2011)
• Possible further evidence for open charm effects in the
cross section lineshape of e+e  c
Puzzles in charmonium decays
 “ puzzle” in J/,   VP decay
 (3770) non-DD decay
 M1 transition problem in J/,    c, ( c)
 Recent puzzling results for J/,    ,  
 Large c (c)  VV branching ratios
 Decays of c1  VV and c2  VP
 Isospin-violating decay of (3770) and   J/ 0,
and
hc0
Conjecture:
1) Could
These puzzles
could …
be related
to non-pQCD mechanisms in

be more
…
charmonium decays due to intermediate D meson loops.
2) The intermediate meson loop transition could be a mechanism for the
evasion of the helicity selection rule.
 “-疑难”和(3770)的非D介子衰变
• QCD理论可以在J/和衰变之间建立起一个简单的关系：
c
g
c
J/, '
c
*
J/, '
c
强衰变
• J/,   衰变严重
偏离这一“12%法则”：
R() =
电磁衰变
 0.2 %
c
• 实验观测的矛盾：
g
(3770)
BES-II发现(3770) 的非D介子对衰变分
支比约为15%；而CLEO-c发现这一衰变
分支比几乎可以忽略（上限约为9%）。
c
非D介子对
强衰变
• 微扰QCD理论计算发现：
[He, Fan, and Chao, PRL101, 112001 (2008)]
非相对论QCD领头阶的计算与CLEO-c的结果一致，但是次领头阶的修正
却极为重要，可以给出约为5%的分支比。
暴露出的问题：
QCD非微扰机制在粲偶素能区可能变得极为重要！
DD衰变阈会通过与“非淬火”效应相关的D介子圈影响(3686) 的衰
变性质，特别是压低  的强衰变振幅强度；同时导致(3770)的
非D介子对衰变的非微扰跃迁。
(3770)
(3770)
c cD
粲
偶
素
质
量
D(cq)
(ud)
c c
D
(3770)
DD 衰变阈
(3686)
D
(ud)
D
(3686)
(du)
c
c
J/(3096)
JPC
D(qc)
(du)
=
1 
(3770) 通过D介子圈衰变到非D介子对末态的
非微扰跃迁机制
可以合理解释(3770)较大的非D介子衰变分支比！
Y.-J. Zhang, G. Li and Q. Zhao, Phys. Rev. Lett. 102, 172001 (2009)
Mechanism suppressing the strong
decay amplitudes of   VP

Open-charm effects as an OZI-rule evading mechanism
J/ ()
c
g
V
J/ ()
c
D
V
D*
c*
SOZI: pQCD dominant
P
c
D
P
OZI-evading: non-pQCD dominant
• Interferences among the single OZI, EM and
intermediate meson loop transitions are unavoidable.
Decomposition of OZI evading long-range loop
transitions
D

D

J/ ()


J/ () D

D*
D
t-channel

J/ ()
…
V


s-channel
Zhang, Li and Zhao, 0902.1300[hep-ph]; Li and Zhao, PLB670, 55(2008)
Recognition of interferences
Property of the anti-symmetric tensor coupling allows a parametrization:
Overall suppression of the  strong decay coupling:
In order to account for the “ puzzle”, a destructive phase between
and
is favored.
Zhao, Li, and Chang, JPG2009
Preliminary results
The same mechanism should contribute in various processes
involving the same charmed meson loops
Nonrelativistic quark model: Isgur et al.
GI: Godfrey and Isgur
Lattice results: Dudek et al., PRD79, 094504 (2009)
Li and Zhao: PLB670, 55 (2008); PRD84, 074005 (2011)
Summary
• Surprises from higher charmonium states could be signals for
nonperturbative mechanisms due to open charms.
• Open charm effects could be essential for understanding
some of those long-standing puzzles in charmonium decays
(3770) non-DD decays
“ puzzle” in J/, ’  VP
M1 transition problem in J/,    c, ( c)
Isospin violating decay of  and (3770) J/0
Helicity selection rule violations (c1 VV, c2VP, c BB …)
Cross section lineshapes of e+e-  DD and DD*+c.c.
……
• Lots of opportunities for experiments accessible this energy
region, such as BES-III, Panda, Super-B …
 To firm up open charm effects …
1) Look for systematic constraints on the model uncertainties
in all relevant processes.
2) Look for effects of hadronic loop contributions as
unquenched effects in charmonium spectrum
(refs.: T. Barnes and E. Swanson, PRC77, 055206 (2008); Li, Meng and Chao,
PRD80, 014012(2009)
3) Compare different theoretical approaches, e.g. NREFT and
ELA in isospin-violating charmonium decays.
(refs.: Guo, Hanhart, and Meissner, PRL(2009); Guo, Hanhart, Li, Meissner, QZ,
PRD(2010); and PRD(2011).)
Part of relevant references:
1. G. Li and Q. Zhao, Phys. Rev. D 84, 074005 (2011), arXiv:1107.2037[hep-ph].
2. Q. Wang, X.-H. Liu and Q. Zhao, Phys. Rev. D 84, 014007 (2011).
3. Q. Zhao, Phys. Lett. B 697, 52 (2011).
4. F.-K. Guo, C. Hanhart, G. Li, Ulf-G. Meißner, Q. Zhao, Phys. Rev. D 83,
034013 (2011); arXiv:1008.3632[hep-ph].
5. X.-H. Liu and Q. Zhao, J. Phys. G 38, 035007 (2011); arXiv:1004.0496 [hepph].
6. F.-K. Guo, C. Hanhart, G. Li, Ulf-G. Meißner, Q. Zhao, Phys. Rev. D 82,
034025 (2010); arXiv:1002.2712[hep-ph].
7. X.-H. Liu and Q. Zhao, Phys. Rev. D 81, 014017 (2010)
8. Y.J. Zhang, G. Li and Q. Zhao, Phys. Rev. Lett. 102, 172001 (2009);
arXiv:0902.1300 [hep-ph].
9. Y.-J. Zhang and Q. Zhao, Phys. Rev. D81, 034011 (2010)
10. Y.J. Zhang and Q. Zhao, Phys. Rev. D 81, 074016 (2010)
11. Q. Zhao, G. Li and C.H. Chang, Chinese Phys. C 34, 299 (2010);
12. G. Li and Q. Zhao, Phys. Lett. B 670, 55(2008).
13. G. Li, Q. Zhao and C.H. Chang, J. Phys. G 35, 055002 (2008)
14. Q. Zhao, G. Li and C.H. Chang, Phys. Lett. B 645, 173 (2007)
Thanks for your attention!
Anomalously large isospin violations:
BESIII@Hadron2011
• Theoretical interpretation: Wu, Liu, Zhao and Zou, arXiv: 1108.3772[hep-ph]
Triangle singularity
a0-f0 mixing
 To pin down the underlying dynamics
Direct test of rho-pi puzzle:
• J/,  PP for the role played by EM annihilations (X.Q. Li)
• c, c  VV for the role played by strong annihilations (Wang,
Liu, QZ)
Indirect tests:
• Helicity selection rule violation processes and correlations
with the OZI rule violations (Liu et al; Liu, Wang, QZ)
• Strong isospin violations via charmed meson loops (Guo,
Hanhart, Li, Meissner, QZ)
• Open charm effects in the cross section lineshape studies
• B meson loops in Upsilon decays (Chao et al)
• Open threshold effects on the charmed meson spectrum
(Barnes et al; Chao and Meng)