Transcript Slide 1

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
[email protected]
2011年11月4日，USTC，合肥
Outline
1. Some facts about quarks
2. Charmonium and charmonium-like states –
resonance or non-resonance?
3. Direct evidence for open charm threshold
effects in e+e-  J/, J/ 0, and c
4. Puzzles in charmonium decays
5. Summary
-- surprising or not?
1. Some facts about quarks
pre-history of sub-atomic particles
1897: electron
Thomson
1919: proton
Rutherford
1932: neutron
Joliet-Curie
Chadwick
1933: positron
C.-Y. Chao Anderson
1935: pion predicted by Yukawa
p
n

Yukawa
From S. Olsen’s summer lecture
in Beijing, 2010
Elementary particle “Zoo” in
1963
meson resonances
“stable” hadrons
baryon resonances
X
S
L
N
K

m
e
X*
K*
w
Y*
r
Two “classes” of hadrons
K2*
“non-strange:”
, r,
“strange:”
L, S,n,K,p,K*,
……
D
From S. Olsen’s summer lecture
in Beijing, 2010
1961: Gell-Mann, Nishijima & Nee’man: The Eightfold Way
Quarks as building blocks of hadrons: meson (qq), baryon (qqq)
Simple rules for quarks (Particle Data Group):
1) Quark has spin 1/2 and baryon number 1/3;
2) Quark has positive parity and antiquark has negative parity;
3) The flavor of a quark has the same sign as its charge.
SU(3) multiplets of baryons made of u, d, and s
SU(3) octet
with JP=1/2+
S
X– (ssd)
2
X0 (ssu)
Gell-Mann - Nishijima:
Q=I3+Y/2=I3+(B+S)/2
1
S–
(sdd)
–1
S+
(suu)
S0, L (sud)
n (dud)
0
p (uud)
1
I3
333
=(3 6)  3
=(18)  (810)
SU(3) multiplets of baryons made of u, d, and s
S
SU(3) decuplet 10
with JP=3/2+
–(sss)

3
X*– (ssd)
S*–
(sdd)
3/2
D–(ddd)
2
1
S*+
(suu)
S*0 (sud)
1
1
D0(udd) 0
Decuplet 10:
–(sss)
X*0 (ssu)
D+(uud)
3/2
D++(uuu)
I3
m3
Symmetric spin wavefunction: S=3/2
Symmetric flavor wavefunction: sss
Symmetric spatial wavefunction: L=0
m1
6/2
2r
A problem encountered:
Violation of the Pauli principle and Fermi-Dirac
statistics for the identical strange quark system?
r3
r1
m2
r2
Jacobi coordinate
• An additional degrees of
freedom, Colour, is introduced.
• Quark carries colour, while
hadrons are colour neutral objects.
333
= (3  6)  3
= (1 8)  (8  10)
Again: Are quarks real objects?
Probe coloured quarks in electron-positron collisions
e
* eq
q
e
Hadrons
e
m
* e
q
m
e
Electron-Positron annihilations
R
  êq2
 (2/3)2  (1/3)2  (1/3)2  …
u
d
s
…
R   êq2
q:
u(3/2)
d(-1/3)
s(-1/3)
c(2/3)
b(-1/3)
(2/3)2  (1/3)2  (1/3)2
R
 [2/3]
 (2/3)2
[2/3]
t(2/3)
 [10/9]
(1/3)2
[10/9]
[11/9]
But if quark carries color, one should have
R  3 êq2
 [11/9]
 (2/3)2  [15/9]
R  3 êq2
q:
u(3/2)
d(-1/3)
s(-1/3)
c(2/3)
b(-1/3)
(2/3)2  (1/3)2  (1/3)2
R
2
 [2/3]
 (2/3)2
[2/3]
t(2/3)
 [10/9]
10/3
(1/3)2
[10/9]
[11/9]
 [11/9]
11/3
 (2/3)2  [15/9]
5
2/3
Particle Data Group 2010
1976 Nobel Prize:
B. Richter and S. C.-C. Ting
"for their pioneering work in the
discovery of a heavy
elementary particle of a new
kind"
Also seen in pNe+e-X

J
R=2.2
>>2/3
10
J.E. Augustine et al., PRL 33, 1406 (1974)
J.J. Aubert et al., PRL 33, 1404 (1974)
Quarks are real building blocks of hadrons: meson (qq), baryon (qqq)
• Quarks are not free due to QCD colour force (colour confinement).
• Chiral symmetry spontaneous breaking gives masses to quarks.
• Hadrons, with rich internal structures, are the smallest objects in
Nature that cannot be separated to be further finer free particles.
Convention (Particle Data Group):
1) Quark has spin 1/2 and baryon number 1/3;
2) Quark has positive parity and antiquark has negative parity;
3) The flavor of a quark has the same sign as its charge.
Quantum Chromo-Dynamics:
a highly successful theory for Strong Interactions
Meson
Confinement
Conventional hadrons
Baryon
Asymp. freedom
Remaining questions:
•Why are the proper effective degrees of freedom for hadron
internal structures?
•What are the possible color-singlet hadrons apart from the
simplest conventional mesons (qq) and baryons (qqq)?
•What’s happening in between “perturbative” and “nonperturbative”?
•… …
Multi-faces of QCD:
Exotic hadrons beyond conventional QM
Hybrid
Hadronic molecule
Glueball
Tetraquark
Pentaquark
The study of hadron structures and hadron spectroscopy
should deepen our insights into the Nature of strong QCD.
2. Charmonium and
charmonium-like states
• Charm quark and charmonium states
Parity:
P=(1)L+1
Charge conjugate:
C=(1)L+S
S=0
c
L
c
J/
S=1
c
L
c

……….
• 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]
3. 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
4. Puzzles in charmonium decays
Puzzles in charmonium decays
 “r 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.

Short-distance dominant – “12% rule”
• pQCD expectation of
the ratio between J/
and ' annihilation:
JPC = 1
c
g
*
J/, '
J/, '
c*
c*
R(r) =
c
 0.2 %
Large “12% rule”
violation in r ! –
“r puzzle”

(3770) non-DD decays
c
 Contradictions in exp.
observations:
(3770)
g
Non-DD
c
Up to 15 %
BES-II:
CLEO-c:
< 9 % at 90% C.L.
Updated results from CLEO-c : 1004.1358[hep-ex]
 Contradictions in pQCD calculations：
• NRQCD leading order calculations gave negligible
contributions from the (3770) non-DD decays.
Refs: Kuang and Yan, PRD41, 155 (1990); Ding, Qin and Chao,
PRD44, 3562 (1991); Rosner, PRD64, 094002 (2001)
• However, calculations including NLO yield significant
corrections.
Ref: He, Fan and Chao, PRL101, 112001 (2008)
pQCD calculation:
BR(non-DD) < 5%
 Short-range pQCD transition;
 Color-octet contributions are
included;
 2S-1D state mixings are small;
 NLO correction is the same
order of magnitude as LO.
 Results do not favor both
CLEO and BES
 NNLO ?
Questions:
1) Would QCD perturbative expansion still be valid in the
charmonium energy region?
2) Would other non-perturbative mechanisms play a role in
(3770)  non-DD ?
 Recognition of possible long-range transition
mechanisms
pQCD (non-relativistic QCD):
Non-pQCD:
If the heavy cc are good
constituent degrees of freedom, c
and c annihilate at the origin of
the (cc) wavefunction. Thus,
NRQCD should be valid.
Are the constituent cc good
degrees of freedom for (3770) 
light hadrons? Or is pQCD
dominant at all?
pQCD is dominant in (3770)
 light hadrons via 3g exchange,
hence the OZI rule will be
respected.
 (3770) non-DD decay
will be suppressed.
If not, how the OZI rule is
violated?
 Could the OZI-rule
violation led to sizeable
(3770) non-DD decay?
 How to quantify it?
The (3686) and (3770) will experience or suffer the most from the DD
open channel effects. Such effects behave differently in the kinematics
below or above the threshold.
Mass
(3770) non-DD decays
(3770)
(3770)
c cD
D(cq)
r(ud)
c c
D
(3770)
DD thresh.
(3686)
D
r(ud)
D
(3686)
(du)
c
c
J/(3096)
“r puzzle”
JPC
D(qc)
(du)
=
1 
(3770) hadronic decays via intermediate D meson
loops
Quantitative study of (3770)  VP is possible.
Y.-J. Zhang, G. Li and Q. Zhao, PRL102, 172001 (2009)
The V  VP transition has only one single
coupling of anti-symmetric tensor form
Transition amplitude can thus be decomposed as:
Long-range nonpQCD amp.
Short-range
pQCD amp.
iii) Predictions for (3770)  VP.
Could become sizeable, i.e. several percents, after add up a
number different channels!
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
r
D

J/ ()

r
J/ () D

D*
D
t-channel
r
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 “r puzzle”, a destructive phase between
and
is favored.
Zhao, Li, and Chang, JPG2009
Preliminary results
 M1 transition problem in J/,    c, ( c)
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)
5. Summary
• Surprises from higher charmonium states could be signals for
nonperturbative mechanisms due to open charm thresholds.
• Open charm effects could be essential for understanding
some of those long-standing puzzles in charmonium decays
(3770) non-DD decays
“r 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).
Thanks for your attention!
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)
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)
More than “r” … …
Branching ratios for J/ (cc)  V P
Same order
of magnitude !
Branching ratios for  V P
Comparable !?
• What accounts for such a large isospin violation?
• Correlation between the helicity selection rule and
OZI rule violations
• Implications of the “r puzzle” …
Theoretical explanations:
1. J/  r is enhanced
• J/-glueball mixing:
Freund and Nambu, Hou and Soni, Brodsky, Lepage and Tuan
Assuming a general validity of the pQCD hadron helicity theorem
• Final state interaction:
Li, Bugg and Zou (light meson loops)
• Intrinsic charmonium component within light vectors:
Brodsky and Karliner, Feldman and Kroll
Mechanisms for evading the helicity selection rule
2. '  r is suppressed
• Karl and Roberts: sequential fragmentation model
• Pinsky: hindered M1 transition model
• Chaichian and Tornqvist: exponential form factor model
• Chen and Braaten: color octet Fock state dominance in J/
• Rosner: ' and " mixing
• Suzuki: possible hadronic excess in (2S) decay due to
intermediate DD
•……
Natural and unnatural …


+/ EM + Long-range int.
3g
+/ EM + Long-range int.
3g
Helicity selection rule violating
• “12% rule” will not hold if EM, and/or other possible
transitions are important.
c
g
V
*
V
J/
J/
c*
c
P
c*
P
The isospin-violating decay channels also fit in “12%” rule?
Rth(%)
Rexp(%)
c
*
V
J/
c*
P
Are quarks real objects?
or just mathematical mnemonics?
助记符 기억하는
“Are quarks actually real objects?" Gell-Mann asked.
"My experimental friends are making a search for them
in all sorts of places -- in high-energy cosmic ray reactions
and elsewhere. A quark, being fractionally charged,
cannot decay into anything but a fractionally charged
object because of the conservation law of electric charge.
Finally, you get to the lowest state that is fractionally
charged, and it can't decay. So if real quarks exist, there is
an absolutely stable quark. Therefore, if any were ever
made, some are lying around the earth."
But since no one has yet found a quark, Gell-Mann
concluded that we must face the likelihood that quarks are
not real.
Slide from S. Olsen
Gell-Mann
Nobel
Prize
1969