1. QCD exotics and production of threshold states Institute of High Energy Physics, CAS Sixth Asia-Pacific Conference on Few-Body Problems in Physics APFB 2014, April 7-11, 2014, Hahndorf, Australia Qiang Zhao Institute of High Energy Physics, CAS and Theoretical Physics Center for Science Facilities (TPCSF), CAS zhaoq@ihep.ac.cn

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 c L S=0,1 cc J=L+S

4. Charged heavy quarkonium states observed in exp. Panel discussion in Charm 2013, Aug. 31-Sept. 4, 2013, Manchester

5. QWG, 1010.5827[hep-ph] X(3900) Close to D  D* threshold X(3872) Y(4260) Y(4360)

6. 1 ,  (c  c)/  (b  b) … ** e+e+ ee Direct production of vector charmonium (J PC =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)? …… Belle, BaBar, and BESIII i) Vector charmonium production in e  e  annihilations c cc qq q Charmed meson pair production, i.e. D(0  )  D(0  ), D*(1  )  D*(1  ), D*  D +  DD*…

7. Belle PRD77, 011103(2008).  (3770), 1D  (4040), 3S  (4160)  (4415) X(3900) ? 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? … … e+e-  D  D Cross section lineshape in e+e- annihilations into D  D pair Y(4260)

8.  (e + e -  hadrons) 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 See 1010.5827[hep-ph] for a recent review. Cited 485 times!

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  D 1 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 Χ c0 ω, M. Shi, D. L. Yao and H.Q. Zheng, hep- ph/1301.4004  Hadro-quarkonium, M. Voloshin  Inference effects, X. Liu et al  ……

12. BESIII, PRL110, 252001 (2013) [arXiv:1303.5949 [hep-ex]] 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). e+e+ ee   J/  Zc Y(4260)

13. Belle, PRL110, 252002 (2013) [arXiv:1304.0121v1 [hep-ex]] Xiao et al., arXiv:1304.3036v1 [hep-ex]

14. BESIII Collaboration, arXiv:1308.2760 [hep-ex]

15. Zc(3900)? m(Zc(4020)) =  (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] Y(4260)

16. J P = 1  J P = 0  J P = 1  BESIII Collaboration, arXiv:1310.1163 [hep-ex] Direct determination of the spin-parity! Zc(3900)?

17. 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? …

18. V(r) =  /r   r Coulomb Linear conf. 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  qq creation Color screening effects? String breaking effects? Breakdown of potential quark model

19. 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 hadronic molecules can be formed by mesons, the following points should be recognized:

20. Q. Wang et al, PRD2012 Y.J. Zhang et al, PRL(2009); X. Liu, B. Zhang, X.Q. Li, PLB(2009) Q. Wang et al. PRD(2012), PLB(2012) The mass shift in charmonia and charmed mesons, E.Eichten et al., PRD17(1987)3090 X.-G. Wu and Q. Zhao, PRD85, 034040 (2012) G. Li and Q. Zhao, PRD(2011)074005 F.K. Guo and Ulf-G Meissner, PRL108(2012)112002 X.-H. Liu et al, PRD81, 014017(2010); X. Liu et al, PRD81, 074006(2010) 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 “  puzzle”

21. 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. u u d d u d d d d u  Proton Neutron Deuteron: p-n molecule Can we learn something from nuclear interaction?

22. 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 Weinberg’s Compositeness Theorem The effective coupling g eff encodes the structure information and can be extracted model-independently from experiment.

23. Y(4260) could be a hadronic molecule made of DD 1 (2420) Q. Wang, C. Hanhart, QZ, PRL111, 132003 (2013); PLB(2013) Y(4260) DD*  W= 4020 MeV DD 1 (2420) W= 4289 MeV D (c  q), J P =0  ; D*(c  q), J P =1  ; D 1 (c  q), J P =1 . D 1 (2420)  D(1868) Y(4260), 1  Y(4260) D1D1 DD D0D0 D*  “threshold state”

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)] J/  D* DD   M(Zc)  M(D) + M(D*) = 3.876 GeV Zc(3900), I,J P = 1, 1  A systematic study of the singularity regions in e+e-  J/psi pipi, hc pipi and DD*pi is necessary.

25. Y(4260)D 1 D coupling: Zc(3900)DD* coupling: D1D*pi coupling: Lagrangians in the NREFT 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:   J/  (hc) D* D D1

27.   J/  Zc   J/  D* D D1 Singularity kinematics in e  e   J/  Wang, Hanhart and Zhao, PLB2013; arXiv: 1305.1997[hep-ph]  (D 1 (2420) = 27 MeV  (D *0 ) = 190 keV

28. BESIII, 1303.5949[hep-ex] “prediction” from a molecular Y(4260) in J/  decay Q. Wang, C. Hanhart, QZ, PRL111, 132003 (2013); PLB(2013)

29. Prediction for Y(4260)  h c  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 BESIII Belle M. Cleven, Q. Wang, C. Hanhart, U.-G. Meissner, and Q. Zhao, 1310.2190. D1DD1D D1DD1D

32. Y(4260) couplings to D 1 D, D 1 D* and D 2 D* : Lagrangians including combinations of spin doublets (D,D*) and (D 1, D 2 ) in the NREFT D 1 D*pi, D 2 Dpi and D 2 D*pi couplings:

33. Prediction for the anomalous cross section line shape Data from Belle D1DD1D D1D*D1D* D2D*D2D*

34. Invariant mass spectra for D , D* , and  DD* Signature for D 1 (2420) via the tree diagram. The Zc(3900) could have a pole below the DD* threshold.

35. M. Cleven, Q. Wang, C. Hanhart, U.-G. Meissner, and Q. Zhao, 1310.2190. Parameters fitted by the cross section lineshapes in J/psi pipi and hcpipi channel

36. The puzzling Y(4260) may have a prominent D 1 D 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. … …

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.

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. new CDF meas. new Belle meas. M D0 + M D*0 3871.8±0.4 MeV = 3871.46 ± 0.19 MeV  m =  0.35 ± 0.41 MeV Observation of X(3872) 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 J PC = 1  is confirmed by LHCb

41. c c cc cc uu uu uu D0D0  D* 0 D0D0 D* 0 00 X(3872) as an analogue to the deuteron X(3872):  D 0 D* 0 with Isospin =0. How about  D 0 D* 0 with Isospin =1? If YES, we will have three states: D 0  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!