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2. physics

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@ihep.ac.cn
Sixth Asia-Pacific Conference on Few-Body Problems in Physics
APFB 2014, April 7-11, 2014, Hahndorf, Australia
Outline
1. Exotic feature of the spectra
-- What drives the “exotic” feature?
2. Open threshold phenomena
-- Production mechanism for threshold states
3. Some remarks
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
Charged heavy quarkonium states observed in exp.
Panel discussion in Charm 2013, Aug. 31-Sept. 4, 2013, Manchester
QWG, 1010.5827[hep-ph]
X(3872)
X(3900)
Close to DD* threshold
Y(4260)
Y(4360)
i) Vector charmonium production in ee annihilations
e+
c
(cc)/(bb) … q
*
1,
q
e
Charmed meson pair
production, i.e.
D(0)D(0),
D*(1)D*(1),
D*D +DD*…
c
Belle, BaBar, and BESIII
Direct production of vector charmonium (JPC=1) states.
Dynamics for vector charmonium interactions with final states.
What’s 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)?
• ……
•
•
•
•
• Cross section lineshape in e+e- annihilations into DD pair
e+e-  DD
• What is X(3900)? (see
Y(4260)
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?
•……
Belle PRD77, 011103(2008).
(e+e-  hadrons)
Y(4260)
Y(4260)
Observation of Y(4260) in J/  spectrum
PRD77, 011105 (2008)
Belle
• Opportunities for a better understanding the nature
of Y(4260)
Cited 485 times!
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
See 1010.5827[hep-ph] for a recent review.
 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 Χc0ω, M. Shi, D. L. Yao and H.Q. Zheng, hepph/1301.4004
 Hadro-quarkonium, M. Voloshin
 Inference effects, X. Liu et al
 ……
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) [arXiv:1303.5949 [hep-ex]]
Belle, PRL110, 252002 (2013) [arXiv:1304.0121v1 [hep-ex]]
Xiao et al., arXiv:1304.3036v1 [hep-ex]
BESIII Collaboration, arXiv:1308.2760 [hep-ex]
Zc(4020)
Zc(3900)?
Y(4260)
m(Zc(4020)) =
(Zc(4020)) =
Both Zc(4025) and Zc(4020) are close to the D*D* threshold. Are they the
same state?
BESIII Collaboration, arXiv:1309.1896 [hep-ex]
Zc(3900)?
Direct determination of the spin-parity!
JP = 1
JP = 1
JP = 0
BESIII Collaboration, arXiv:1310.1163 [hep-ex]
BESIII, PRL110, 252001 (2013) [arXiv:1303.5949 [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?
• ……
Breakdown of potential quark model
Linear conf.
qq creation
Coulomb
V(r) = /r   r
• 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
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?
• 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)
“ puzzle”
Q. Wang et al. PRD(2012), PLB(2012)
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)
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
d
Neutron
u
Deuteron: p-n molecule
Weinberg’s 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.
Y(4260) could be a hadronic molecule made of DD1(2420)
Y(4260)
DD*
W= 4020 MeV
D (cq), JP=0;
DD1(2420)
D*(cq), JP=1;
D1 (cq), JP=1.
W= 4289 MeV
“threshold state”
Y(4260),
1
D1(2420)
D(1868)
Y(4260)
D1
D*

D
Q. Wang, C. Hanhart, QZ, PRL111, 132003 (2013); PLB(2013)
D0
• 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)]
D*
J/
Zc(3900), I,JP= 1, 1

D

M(Zc)  M(D) + M(D*) = 3.876 GeV
A systematic study of the singularity regions in e+e-  J/psi pipi, hc pipi
and DD*pi is necessary.
Lagrangians in the NREFT
• Y(4260)D1D coupling:
• Zc(3900)DD* coupling:
• D1D*pi coupling:
Q. Wang, C. Hanhart, QZ, PRL111, 132003 (2013); PLB(2013)
• 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)
Singularity kinematics in ee J/

D1
D

D*

J/

Zc
J/
(D1(2420) = 27 MeV
(D*0) = 190 keV
Wang, Hanhart and Zhao, PLB2013; arXiv: 1305.1997[hep-ph]
“prediction” from a molecular Y(4260) in J/ decay
BESIII, 1303.5949[hep-ex]
Q. Wang, C. Hanhart, QZ, PRL111, 132003 (2013); PLB(2013)
Prediction for Y(4260)  hc  with  final state interactions
Q. Wang, C. Hanhart, and Q. Zhao, PRL111, 132003 (2013).
Singularity kinematics in Y(4170)  J/psi 
CLEO results
Q. Wang, C. Hanhart, and Q. Zhao, PLB725, 106 (2013).
Further test of the Y(4260) and Zc(3900) properties in the cross section line
shape measurement
Belle
D1D
BESIII
D1D
M. Cleven, Q. Wang, C. Hanhart, U.-G. Meissner, and Q. Zhao, 1310.2190.
Lagrangians including combinations of spin doublets (D,D*)
and (D1, D2) in the NREFT
• Y(4260) couplings to D1D, D1D* and D2D* :
• D1D*pi, D2Dpi and D2D*pi couplings:
Prediction for the anomalous cross section line shape
D1D
D1D*
D2D*
Data from Belle
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.
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.
• 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), Zb’s, and Zc’s, 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.
•……
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.
Seventh Asia-Pacific Conference on Few-Body
Problems in Physics, APFB 2017, China
Date? Venue? …
Please come and enjoy!
Thanks for your attention!
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 = 1 is confirmed by LHCb
X(3872) as an analogue to the deuteron
c
D*0
u
u
c
D0
c
0
D
u
0
u
0
D*
c
• X(3872): D0D*0 with Isospin =0.
• How about D0D*0 with Isospin =1? If YES, we will
have three states:
D0D*0 +c.c. : [cu uc]
DD*0 +c.c. : [cd uc]
DD*0 +c.c. : [cu dc]
Charged charmonium states!