Qiang Zhao Institute of High Energy Physics, CAS and Theoretical Physics Center for Science Facilities (TPCSF), CAS “Surprises” from charmonium decays Institute of High Energy Physics, CAS 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 -- surprising or not? 5. Summary

1. Some facts about quarks

pre-history of sub-atomic particles 1897: electron 1919: proton 1932: neutron 1933: positron 1935: pion predicted by Yukawa Yukawa C.-Y. ChaoAnderson Joliet-Curie Chadwick Rutherford Thomson pn  From S. Olsen’s summer lecture in Beijing, 2010

Elementary particle “Zoo” in 1963 “stable” hadrons meson resonances baryon resonances Two “classes” of hadrons “non-strange:” n, p, ,  … “strange:” , , K, K*, … “flavors”     K   e K*   K2*K2* Y*  ** 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.

S n (dud)p (uud)  – (sdd)  – (ssd)  0,  (sud)  + (suu)  0 (ssu) I3I3 SU(3) octet with J P =1/2 + 0 11 22 –1–11 Gell-Mann - Nishijima: Q=I 3 +Y/2=I 3 +( B +S)/2 3  3  3 =(  3  6)  3 =(1  8)  (8  10) SU(3) multiplets of baryons made of u, d, and s

SU(3) decuplet 10 with J P =3/2 + S  0 (udd)  + (uud)  * – (sdd)  * – (ssd)  * 0 (sud)  * + (suu)  * 0 (ssu) I3I3 0 11 22 1  – (ddd)  – (sss) 33 11  ++ (uuu) 3/2  3/2 SU(3) multiplets of baryons made of u, d, and s Decuplet 10:  – (sss)

m1m1 m2m2 m3m3 r1r1 r2r2 r3r3 22  6 /2 Jacobi coordinate Symmetric spin wavefunction: S=3/2 Symmetric flavor wavefunction: sss Symmetric spatial wavefunction: L=0 A problem encountered: Violation of the Pauli principle and Fermi-Dirac statistics for the identical strange quark system? 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?

** ee ee Electron-Positron annihilations Probe coloured quarks in electron-positron collisions q qq Hadrons   ** ee ee eqeq e R    ê q 2  (2/3) 2  (1/3) 2  (1/3) 2  … u d s …

R   ê q 2 q : u(3/2) d(-1/3) s(-1/3) c(2/3) b(-1/3) t(2/3) R (2/3) 2  (1/3) 2  (1/3) 2  [2/3] [2/3]  (2/3) 2  [10/9] [10/9]  (1/3) 2  [11/9] [11/9]  (2/3) 2  [15/9] But if quark carries color, one should have R  3  ê q 2

q : u(3/2) d(-1/3) s(-1/3) c(2/3) b(-1/3) t(2/3) R (2/3) 2  (1/3) 2  (1/3) 2  [2/3] [2/3]  (2/3) 2  [10/9] [10/9]  (1/3) 2  [11/9] [11/9]  (2/3) 2  [15/9] 2 10/3 11/3 5

2/3 Particle Data Group 2010

10  J.J. Aubert et al., PRL 33, 1404 (1974) J.E. Augustine et al., PRL 33, 1406 (1974) J Also seen in pN  e + e - X R=2.2 >>2/ 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"

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. 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. 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.

Quantum Chromo-Dynamics: a highly successful theory for Strong Interactions Conventional hadrons Asymp. freedom Confinement Meson Baryon

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 “non- perturbative”? …

Multi-faces of QCD: Exotic hadrons beyond conventional QM Hybrid Glueball Tetraquark Pentaquark Hadronic molecule 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 c L S=0 cc c L S=1 cc Parity: P=(  1) L+1 Charge conjugate: C=(  1) L+S ………. J/  

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 non- standard configurations, e.g. tetraquarks, hybrids, etc. Greatly enrich our knowledge about strong QCD. Recent experimental progress

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

[hep-ph]

new CDF meas. new Belle meas. M D0 + M D* ±0.4 MeV = ± 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 = 2  is not ruled out

A good candidate for hadronic molecule (Tornqvist 1991) u u d d u d d d d u  Proton Neutron Deuteron: p-n molecule Nature of X(3872) The compositeness criterion can be applied Tremendous contributions from theory commu. A B C. Z B X =  0.35 ± 0.41 MeV

Charged charmonium-like states Resonant structure Z(4430) –Close to D *   D 0 1 threshold –Q =  1, J P = 0 ,1 ,2  –M= 4433 MeV –  = 45 MeV S.K. Choi et al., PRL 100, (2008) First direct evidence for an exotic quark configuration, i.e. (c  c u  d).

arXiv: [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 )

[hep-ph] X(3900) Close to D  D* threshold

1 ,  … ** e+e+ ee Direct production of vector charmonium states Dynamics for charmonium interactions with final states Signals for exotics? X(3900)? … Belle, BaBar, and BEPC-II i) Charmonium production in e  e     final particles

Pakhlova et al., Belle Colla., PRD77, (2008). Y.-J. Zhang and Q. Zhao, PRD81, (2010)  (3770), 1D  (4040), 3S  (4160)  (4415) X(3900) ? What is X(3900)? Not inlcuded in PDG2010. Not in charmonium spectrum … … e+e-  D  D Open charm effects in the cross section lineshape studies

Y.J. Zhang and QZ, PRD81, (2010) e+e-  D  D* + c.c. e+e-  D  D D  D* open threshold may explain:

ii) Direct evidence for open charm effects in e  e   J/  , J/   0  (3770) J/  (I=0)  (I=0) D0D0 D0D0 D* 0 (I=0)  0 (I=1) If m u = m d,  m(D 0 ) = m(D  ) (a) + (b) = 0 If m u  m d,  m(D 0 )  m(D  ) (a) + (b)  0 DD DD D*  (a)(b)  0 (I=1) For the isospin-violating J/  0 production:

Cross section lineshape of e + e   J/  

Direct evidence for open charm effects in the cross section lineshape of Wang, Liu, Zhao, [hep-ph], PRD84, (2011) e + e   J/   0 ~ 8 MeV

Possible further evidence for open charm effects in the cross section lineshape of e + e    c

4. 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 h c  0 Could be more … … Conjecture: 1)These puzzles could be related to non-pQCD mechanisms in 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. Puzzles in charmonium decays

pQCD expectation of the ratio between J/  and  ' annihilation: c J/ ,  ' g c c* ** J/ ,  ' c* J PC = 1   Short-distance dominant – “12% rule” R(  ) =  0.2 % Large “12% rule” violation in  ! – “  puzzle”

c  (3770) g cc Non-D  D  Contradictions in exp. observations: BES-II: CLEO-c: Up to 15 % < 9 % at 90% C.L. Updated results from CLEO-c : [hep-ex]   (3770) non-D  D decays

 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, (2001) However, calculations including NLO yield significant corrections. Ref: He, Fan and Chao, PRL101, (2008)

 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 ? pQCD calculation: BR(non-D  D) < 5% 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):  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.  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. Non-pQCD:  Are the constituent c  c good degrees of freedom for  (3770)  light hadrons? Or is pQCD dominant at all?  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?

J/  (3096)  (3686)  (3770) D  D thresh. Mass J PC = 1   c cc  (3770) D(c  q)  D(q  c)  (3686) c cc (ud)(ud) (du)(du) 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. D DD “  puzzle”  (3770) non-D  D decays  (3770) c cc (ud)(ud) (du)(du) D DD

 (3770) hadronic decays via intermediate D meson loops Y.-J. Zhang, G. Li and Q. Zhao, PRL102, (2009) Quantitative study of  (3770)  VP is possible.

Transition amplitude can thus be decomposed as: The V  VP transition has only one single coupling of anti-symmetric tensor form Short-range pQCD amp. Long-range non- pQCD amp.

iii) Predictions for  (3770)  VP. Could become sizeable, i.e. several percents, after add up a number different channels!

Open-charm effects as an OZI-rule evading mechanism J/  (  ) c cc V D DD D* Interferences among the single OZI, EM and intermediate meson loop transitions are unavoidable.  Mechanism suppressing the strong decay amplitudes of   VP c c* V P g P J/  (  ) SOZI: pQCD dominant OZI-evading: non-pQCD dominant

J/  (  )   t-channel J/  (  )   V     s-channel Decomposition of OZI evading long-range loop transitions D DD DD D D*  … … Zhang, Li and Zhao, [hep-ph]; Li and Zhao, PLB670, 55(2008)

Recognition of interferences Property of the anti-symmetric tensor coupling allows a parametrization: Zhao, Li, and Chang, JPG2009 In order to account for the “  puzzle”, a destructive phase between andis favored. Overall suppression of the  strong decay coupling:

Preliminary results

The same mechanism should contribute in various processes involving the same charmed meson loops M1 transition problem in J/ ,     c, (   c )

Nonrelativistic quark model: Isgur et al. GI: Godfrey and Isgur Lattice results: Dudek et al., PRD79, (2009) Li and Zhao: PLB670, 55 (2008); PRD84, (2011)

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 “  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 … 5. Summary

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, (2008); Li, Meng and Chao, PRD80, (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).) To firm up open charm effects …

Part of relevant references: 1.G. Li and Q. Zhao, Phys. Rev. D 84, (2011), arXiv: [hep-ph]. 2.Q. Wang, X.-H. Liu and Q. Zhao, Phys. Rev. D 84, (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, (2011); arXiv: [hep-ph]. 5.X.-H. Liu and Q. Zhao, J. Phys. G 38, (2011); arXiv: [hep- ph]. 6.F.-K. Guo, C. Hanhart, G. Li, Ulf-G. Meißner, Q. Zhao, Phys. Rev. D 82, (2010); arXiv: [hep-ph]. 7.X.-H. Liu and Q. Zhao, Phys. Rev. D 81, (2010) 8.Y.J. Zhang, G. Li and Q. Zhao, Phys. Rev. Lett. 102, (2009); arXiv: [hep-ph]. 9.Y.-J. Zhang and Q. Zhao, Phys. Rev. D81, (2010) 10.Y.J. Zhang and Q. Zhao, Phys. Rev. D 81, (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, (2008) 14.Q. Zhao, G. Li and C.H. Chang, Phys. Lett. B 645, 173 (2007) Thanks for your attention!

Anomalously large isospin violations: Theoretical interpretation: Wu, Liu, Zhao and Zou, arXiv: [hep-ph] Triangle singularitya0-f0 mixing

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) To pin down the underlying dynamics

Branching ratios for J/  (c  c)  V P Same order of magnitude ! More than “  ” … …

Comparable !? Branching ratios for  V P Particle Data Group What accounts for such a large isospin violation? Correlation between the helicity selection rule and OZI rule violations Implications of the “  puzzle” …

Theoretical explanations: 1. J/    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.  '   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 … …

3g “12% rule” will not hold if EM, and/or other possible transitions are important. c c* V P J/  g c c* V P J/  **  +/  EM + Long-range int. Natural and unnatural … Helicity selection rule violating

R th (%) R exp (%) The isospin-violating decay channels also fit in “12%” rule? c c* V P J/  **

Are quarks real objects? or just mathematical mnemonics? 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. Gell-Mann Nobel Prize 1969 助记符 Slide from S. Olsen