Qiang Zhao

1
Institute of High Energy Physics, CAS
QCD exotics and production of threshold states

• Qiang Zhao
• Institute of High Energy Physics, CAS
• and Theoretical Physics Center for Science
  Facilities (TPCSF), CAS
• zhaoq_at_ihep.ac.cn

Sixth Asia-Pacific Conference on Few-Body
Problems in PhysicsAPFB 2014, April 7-11, 2014,
Hahndorf, Australia
2
Outline

1. Exotic feature of the spectra -- What drives
   the exotic feature?
2. Open threshold phenomena -- Production
   mechanism for threshold states
3. Some remarks

3
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
S0,1
c
?c
L
JLS
4
Charged heavy quarkonium states observed in exp.
Panel discussion in Charm 2013, Aug. 31-Sept. 4,
2013, Manchester
5
QWG, 1010.5827hep-ph
X(3872)
X(3900)
Close to D?D threshold
Y(4260)
Y(4360)
6
i) Vector charmonium production in e?e?
annihilations
c
1??, ?(c?c)/?(b?b)
?q
Charmed meson pair production, i.e. D(0?)?D(0?),
D(1?)?D(1?), D?D ?DD
e
?
q
e?
?c
Belle, BaBar, and BESIII

• Direct production of vector charmonium (JPC1??)
  states.
• Dynamics for vector charmonium interactions with
  final states.
• Whats the role played by the S-wave thresholds?
• Signals for vector exotics, e.g. Y(4260)? Or
  exotics produced in vector charmonium decays,
  e.g. X(3872) and Zc(3900)?

7

• Cross section lineshape in ee- annihilations
  into D?D pair

?(3770), 1D
?(4040), 3S
X(3900) ?
ee- ? D?D
?(4160)
?(4415)

• What is X(3900)? (see Wang et al., PRD84, 014007
  (2011))
• X(3900) has not been inlcuded in PDG2010 and
  PDG2012.
• Not in charmonium spectrum
• Why Y(4260) is not seen in open charm decays?

Y(4260)
Belle PRD77, 011103(2008).
8
?(ee- ? hadrons)
Y(4260)
Y(4260)
9
Observation of Y(4260) in J/? ?? spectrum
PRD77, 011105 (2008)
Belle
10

• Opportunities for a better understanding the
  nature of Y(4260)
• Theoretical prescriptions
• Hybrid
• Tetraquark
• Glueball
• Hadronic molecules
• Interference effects
• Calculations done by various approaches
• Quark model
• Hadron interaction with effective potentials
• QCD sum rules
• Lattice QCD

Cited 485 times!
See 1010.5827hep-ph for a recent review.
11

• Hybrid state, F.E.Close and P.R.Page,
  PLB28(2005)215 S.L.Zhu, PLB625(2005)212 E. Kou
  and O. Pene, PLB631(2005)164
• Radial excitation of a diquark-antidiquark state
  analogous to X(3872), L.Maiani, F.Piccinini,
  A.D. Polosa and V. Riquer, PRD71(2005)014028
• D1 D molecular state, G.J.Ding,
  PRD79(2009)014001 F. Close and C. Downum,
  PRL102(2009)242003 A.A.Filin, A. Romanov, C.
  Hanhart, Yu.S. Kalashnikova, U.G. Meissner and
  A.V. Nefediev, PRL105(2010)019101
• Strongly couple to ?c0?, M. Shi, D. L. Yao and
  H.Q. Zheng, hep-ph/1301.4004
• Hadro-quarkonium, M. Voloshin
• Inference effects, X. Liu et al

12
e
?
Y(4260)
?
e?
Zc
J/?

• The mass of the charged charmonium-like
  structure Zc(3900) is about 3.899 GeV, close to
  DD threshold!
• It could be an opportunity for understanding the
  mysterious Y(4260).

BESIII, PRL110, 252001 (2013) arXiv1303.5949
hep-ex
13
Belle, PRL110, 252002 (2013) arXiv1304.0121v1
hep-ex
Xiao et al., arXiv1304.3036v1 hep-ex
14
BESIII Collaboration, arXiv1308.2760 hep-ex
15
Zc(4020)
Zc(3900)?
Y(4260)
m(Zc(4020))
?(Zc(4020))
Both Zc(4025) and Zc(4020) are close to the ?DD
threshold. Are they the same state?
BESIII Collaboration, arXiv1309.1896 hep-ex
16
Zc(3900)?
Direct determination of the spin-parity!
JP 1?
JP 1?
JP 0?
BESIII Collaboration, arXiv1310.1163 hep-ex
17

• BESIII, PRL110, 252001 (2013) arXiv1303.5949
  hep-ex
• Theoretical interpretations
• Hadro-quarkonium (M. Voloshin et al.)
• Tetraquark (L. Maiani et al.)
• Born-Oppenheimer tetraquark (E. Braaten)
• Hadron loops (X. Liu et al.)
• Hadronic molecule produced in a singularity
  condition (Q. Wang, C. Hanhart, Q.Z.)

• Would Zc(3900) and Zc(4020/4025) be an analogue
  of the Zb and Zb in the charm sector?
• How those states are formed? Are there always
  thresholds correlated?
• What is the dominant decay channel of Zc and Zc
  ?
• What can we learn about the production mechanism
  for Zc and Zc from the lineshape measurement of
  J/psi pipi and hcpipi ?
• How to distinguish various proposed scenarios?

18
Breakdown of potential quark model
Linear conf.
V(r) ??/r ? ? r
?qq creation
Coulomb

• Color screening effects? String breaking effects?
  

• The effect of vacuum polarization due to
  dynamical quark pair creation may be manifested
  by the strong coupling to open thresholds and
  compensated by that of the hadron loops, i.e.
  coupled-channel effects.

E. Eichten et al., PRD17(1987)3090 B.-Q. Li and
K.-T. Chao, Phys. Rev. D79, 094004 (2009) T.
Barnes and E. Swanson, Phys.Rev. C77 (2008)
055206
19
In case that hadronic molecules can be formed by
mesons, the following points should be
recognized

• The constituent mesons are in a relative S wave
  as a prerequisite.
• Similar to the nuclear force, the long range
  interaction may play a crucial role.
• Different from the nuclear force, the nuclear
  repulsive core is not obvious. The role of the
  annihilation potential is not clear.
• The open threshold has strong impact on the
  spectrum.
• -- How to stabilize the hadronic molecular states
  made of mesons?
• -- How to recognize the molecular scenario in the
  spectroscopy?
• -- Do we have a coherent picture for
  understanding those XYZ states in heavy
  quarkonium spectrum?

20

• In case that the open threshold coupled channels
  play a role, typical ways to include such an
  effect are via hadron loops in hadronic
  transitions

Q. Wang et al, PRD2012
X.-H. Liu et al, PRD81, 014017(2010) X. Liu et
al, PRD81, 074006(2010)
Y.J. Zhang et al, PRL(2009) X. Liu, B. Zhang,
X.Q. Li, PLB(2009) Q. Wang et al. PRD(2012),
PLB(2012)
?? puzzle
G. Li and Q. Zhao, PRD(2011)074005 F.K. Guo and
Ulf-G Meissner, PRL108(2012)112002
The mass shift in charmonia and charmed mesons,
E.Eichten et al., PRD17(1987)3090 X.-G. Wu and Q.
Zhao, PRD85, 034040 (2012)
21
Can we learn something from nuclear interaction?
Hadronic molecule an analogue to Deuteron
Heavy-light quark-antiquark pairs form heavy
mesons, and the meson-antimeson pair moves at
distances longer than the typical size of the
meson. The mesons are interacting through
exchange of light quarks and gluons, similar to
nuclear force.
Proton
u
d
u
?
d
Neutron
d
u
Deuteron p-n molecule
22
Weinbergs Compositeness Theorem
Weinberg (1963) Morgan et al. (1992) Baru,
Hanhart et al. (2003) G.-Y. Chen, W.-S. Huo, Q.
Zhao (2013) ...
? Probability to find the hadronic molecule
component in the physical state A
The effective coupling geff encodes the structure
information and can be extracted
model-independently from experiment.
23
Y(4260) could be a hadronic molecule made of
DD1(2420)
D (c?q), JP0? D(c?q), JP1? D1 (c?q), JP1?.
Y(4260)
DD?
DD1(2420)
W 4020 MeV
W 4289 MeV
threshold state
D1(2420)
D1
D
Y(4260), 1??
Y(4260)
?
?D(1868)
?D
?D0
Q. Wang, C. Hanhart, QZ, PRL111, 132003 (2013)
PLB(2013)
24

• The signature of Y(4260) could be revealed by
  the associated Zc(3900) near the DD threshold
  via triangle singularity!
• J.-J. Wu, X.-H. Liu, B.-S. Zou, and Q.
  Zhao, PRL108, 081003 (2012)

Zc(3900), I,JP 1, 1?
J/?
D
?
?
?D
M(Zc) ? M(D) M(D) 3.876 GeV
A systematic study of the singularity regions in
ee- ? J/psi pipi, hc pipi and DDpi is
necessary.
25
Lagrangians in the NREFT

• Y(4260)D1D coupling

• Zc(3900)DD coupling

• D1Dpi coupling

Q. Wang, C. Hanhart, QZ, PRL111, 132003 (2013)
PLB(2013)
26

• The implementation of Weinberg theorem is
  possible
• S-wave dominates in the production of Zc(3900)
• S-wave dominates in DD scattering to J/psi pi
• The Zc(3900) decays into hc pi is not
  necessarily suppressed by the NREFT power
  counting

Non-local pion radiation via triangle singularity
kinematics
?
D1
D
D
?
J/? (hc)
27
Singularity kinematics in e?e?? J/???
?
D1
?
D
?
D
?
Zc
J/?
J/?
?(D1(2420) 27 MeV ?(D0) 190 keV
Wang, Hanhart and Zhao, PLB2013 arXiv
1305.1997hep-ph
28
prediction from a molecular Y(4260) in J/???
decay
BESIII, 1303.5949hep-ex
Q. Wang, C. Hanhart, QZ, PRL111, 132003 (2013)
PLB(2013)
29
Prediction for Y(4260) ? hc ?? with ?? final
state interactions
Q. Wang, C. Hanhart, and Q. Zhao, PRL111, 132003
(2013).
30
Singularity kinematics in Y(4170) ? J/psi ??
CLEO results
Q. Wang, C. Hanhart, and Q. Zhao, PLB725, 106
(2013).
31
Further test of the Y(4260) and Zc(3900)
properties in the cross section line shape
measurement
Belle
BESIII
D1D
D1D
M. Cleven, Q. Wang, C. Hanhart, U.-G. Meissner,
and Q. Zhao, 1310.2190.
32
Lagrangians including combinations of spin
doublets (D,D) and (D1, D2) in the NREFT

• Y(4260) couplings to D1D, D1D and D2D

• D1Dpi, D2Dpi and D2Dpi couplings

33
Prediction for the anomalous cross section line
shape
D1D
D1D
D2D
Data from Belle
34
Invariant mass spectra for D?, D?, and ?DD
Signature for D1(2420) via the tree diagram.
The Zc(3900) could have a pole below the DD
threshold.
35
Parameters fitted by the cross section lineshapes
in J/psi pipi and hcpipi channel
M. Cleven, Q. Wang, C. Hanhart, U.-G. Meissner,
and Q. Zhao, 1310.2190.
36

• The puzzling Y(4260) may have a prominent D1D
  molecular component.
• Given the existence of a pole structure for
  Zc(3900), its production will be driven by the
  low-momentum DD scattering via triangle
  singularity.
• The threshold phenomena explains the significant
  heavy quark spin symmetry breaking.
• Experimental observations of those threshold
  states , e.g. Z(4430), Zbs, and Zcs, have
  significantly enriched the hadron spectroscopy
  which are beyond the simple ?qq picture. The
  study of the production mechanisms for those
  states will provide novel insights into the
  underlying dynamics.

37
3. Some remarks -- We are far from knowing
the detailed properties of the strong QCD in
hadron structure and hadron interactions. The
observation of those threshold states expose
another face of the strong QCD apart from the
nuclear interaction.
38
(No Transcript)
39
Seventh Asia-Pacific Conference on Few-Body
Problems in Physics, APFB 2017, China
Date? Venue?
Please come and enjoy!
Thanks for your attention!
40
Observation of X(3872)
new Belle meas.

ltMXgt 3871.46 0.19 MeV
new CDF meas.
MD0 MD0 3871.80.4 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 1?? is confirmed by LHCb

41
X(3872) as an analogue to the deuteron
?c
?c
?D0
?D0
u
u
?0
?u
?u
D0
D0
c
c

• X(3872) ?D0D0 with Isospin 0.
• How about ?D0D0 with Isospin 1? If YES, we will
  have three states

D0?D0 c.c. c?u u?c D??D0 c.c. c?d
u?c D??D0 c.c. c?u d?c
Charged charmonium states!