Exotic Hadrons (奇特强子态) Changzheng YUAN (苑长征) (BES & Belle Collaborations) 中国科技大学 2009年10月23日

2 Hadrons ： normal & exotic Hadrons are composed from 2 (meson) or 3 (baryon) quarks Quark model QCD allows hadrons with N quarks  2, 3 –glueball： N quarks = 0 (gg, ggg, …) –hybrid： N quarks = 2 + excited gluon –Multiquark state： N quarks > 3 –molecule： bound state of more than 2 hadrons

3 A bit of history on exotics hunting “The absence of exotics is one of the most obvious features of QCD” – R. L. Jaffe, 2005 Deuteron  H state, d’, d*,  -  - bound state No solid signature of glueballs Pentaquark state appeared and disappeared (“The story of pentaquark shows how poorly we understand QCD” – F. Wilczek, 2005) Do we still have hope? Yes!

4 Outline The XYZ states at B-factories + other experiments XYZ  charmonium + light meson X(3872) – molecular state? XYZ(3940) & X(3915) – charmonia? Y(4140) & X(4350) – tetraquark states? Y states in ISR – hybrids? Z + (4430)/Z + (4050)/Z + (4250) – cannot be charmonia!  (1S)   +X/Y – new results from Belle! Opportunity at BESIII and other experiments.

5 Most of the XYZ from B-factories + BES, CDF, D0

6 Charmonium spectroscopy Mass (MeV) J PC (2S+1) L J Open charm threshold.  (3770)  (4040) (potential Models) cc ’c’c J/  ’’  c2  c1  c0 hchc  (4415) We were very pride: Potential models worked well for charmonium. No big progress in last century!  (4160) hchc

7 Then we found lots of XYZ states M(MeV) J PC (2S+1) L J Open charm threshold  (3770)  (4040)  (4160) (potential Models) cc ’c’c J/  ’’  c2  c1  c0 X ZY X(3872)  (4415) XYZ(3940) X(3915) X(4160) Y(4008) Y(4140) Y(4260) Y(4360) X(4350) Y(4660) X(3915) X(4160) Y(4008) Y(4140) Y(4260) Y(4360) X(4350) Y(4660) Z(4430) Z(4250) Z(4050) Y (4140) What are they ? Charmonium? Hybrid? Tetraquark? Molecule? … Not all XYZ states are charmonia! hchc ? Y

8 X(3872) first and most puzzling state (observed in 2003 at Belle)

9 X(3872)      J/  arXiv: fb -1 = (2.7±1.6±0.4) MeV PRD77, (2008) 413 fb -1 recent results B ±  XK ± B 0  XK 0 N s =93±  N s =9±5 2.3 

10 X(3872)      J/  in CDF recent results arXiv: ~6000 events! M X = ± 0.16 ± 0.19 MeV  M X < % CL Fits for 2 nearby states

11 M(X(3872))     J/  mode only new CDF meas. PRL103, new Belle meas. M D0 + M D*0. = ± 0.19 MeV  m = ± 0.41 MeV BES III can improve on this No sign of a mass doublet a la Maiani et al  m(deuteron) = -2.2 MeV PRL103, (2009)

12 Mass in X 3872  D* 0 D 0 414fb -1 D 0 D 0  0 Belle 2006, 414/fb X 3872  D 0 D 0  0 BaBar 2006, 347/fb X 3872  D 0 D* 0 (  0 D 0,  D 0 ) Fit with truncated BW in both exps. Is this the higher mass partner state predicted by Maiani et al?

13 Belle update 605fb -1 D 0 D* 0 (D 0  605fb -1 D 0 D* 0 (D 0  0 ) Fit with a phase-space modulated BW Can also use other parameterizations to do the fit N signal = 48±11 evts Signif.=8.8  Agree with  J/  mode.

14 X(3872)   J/  &  ’ from BaBar X(3872)  J/  X(3872)   S  BABAR PRL 102, (2009) 3.0  3.5  Bf(B +  X 3872 K + )×(X 3872  J/  ) =(2.8 ± 0.8 ± 0.2) × Bf(B +  X 3872 K + )×(X 3872  ’  ) =(9.5 ± 2.7 ± 0.9) × C-parity = +1 (Belle also measured  J/  : ) J PC = 2 -+ disfavored  multipole suppression Bf(X 3872   ’) > Bf(X 3872   J/  )  bad for molecules Swanson PLB 598, 197 (2004)

15 B  K  X(3872) from Belle arXiv: fb -1 ~90 events Very weak K*(890) M(K  ) in GeV M(  J/  ) in GeV Backgrounds from J/  sidebands Bf(B  J/  K* 0 )/Bf(B  J/  K  NR ) ~ 4. Similar ratios for  c1,  (2S)! X is very different from other charmonia. Pure 3-body B decays? Check Dalitz plot!

16 Production of X(3872) in B decays

17 Decay of X(3872)

18 Decay of X(3872)

19 X(3872) summary Mass: Very close to D 0 D *0 threshold Width: Very narrow, < 3 MeV J PC =1 ++ favoured Production –in pp collison – similar to charmonia –In B decays – KX similar to cc, K*X smaller than cc Decay BR: open charm ~ 50%, charmonium~O(%) Nature (very likely exotic) –Loosely D 0 D *0 bound state (like deuteron?)? –Mixture of excited  c1 and D 0 D *0 bound state? –Many other possibilities (if it is not  c1, where is  c1 ?)

20 The states near 3940 MeV -circa M = ± 6 MeV  tot = ±12 MeV Nsig = ± 11 evts PRL 100, e + e -  J/  DD* M(DD*) M≈3940 ± 11 MeV  ≈ 92 ± 24 MeV PRL94, M(  J/  ) B  K  J/  M = 3929±5±2 MeV  tot = 29±10±2 MeV Nsig = 64 ± 18 evts   DD M(DD) PRL 96, X(3940)Y(3940) Z(3930) not seen in  J/  not seen in DD*Probably the  c2 ’ probably different BaBar: PRL 101, M≈3914 ± 5 MeV  ≈ 33 ± 10 MeV

21 New peak in    J/  X M: 3914  3  2 MeV,  : 23  MeV, N res = 55  events Signif. = 7.7 , preliminary Background only fit

22 Could it be the Z(3930)? M: 3914  3  2 MeV,  : 23  MeV, N res = 55  evts M = 3929±5±2 MeV  tot = 29±10±2 MeV Nsig = 64 ± 18 evts   DD    J/ 

23   partial width   B(  J/  ) = 69  eV (J P =0 + )   B(  J/  ) = 21  4 +2 eV (J P =2 + ) For comparison:  :   B( DD ) = 180  50 ± 30 eV If X(3915) = Z(3930) =  c2 ’   0.08 B(  c2 ’   J/  ) B(  c2 ’  DD) Huge for above-open-charm-threshold charmonium

24 The 4 states near 3940 X(3940) Y(3940) Belle Z(3930) Mass(GeV) This X(3915) Width(GeV) Range:  (  (stat.)  (sys.)) Good overlap with BaBar “Y(3940)” values

25 cc assignments for X(3915), X(3940) & Y(3940)? 3940MeV Y(3940) = X(3915) =  co ’ ?   (  J/  ) too large? X(3940) =  c ”?  mass too low?  (3S)=4040 MeV Z(3940) =  c2 ’ ?  (  M(J=2,0)=15±7 MeV?) c”c”  c ’’’ 3915MeV  c0 ’

States decaying into J/  Evidence for Y(4140) and a New Resonance at 4.35 GeV

27 The CDF Y(4140)   J/  B +  Y(4140)K + 14±5 events, >3.8  Mass: ± 2.9 ± 1.2 MeV Width: ± 3.7 MeV (It is narrow!) PRL102, (2009) D* s D* s molecule? [cscs] tetraquark?

28  Belle: B→J/ψ  K with 772M BB M(J/ψ  ) fit with Y(4140) parameters fixed [but low effciency at J/  threshold] Y(4140) not significant at BellePreliminary

29 Searched for in    J/  No Y(4140) A few events accumulate at 4.35 GeV in both J/   ee and  modes preliminary 825 /fb J P =0 + : Γ γγ Br(Y(4140)) →  J/  ) < 39 90% C.L. J P =2 + : Γ γγ Br(Y(4140)) →  J/  ) < % C.L.

30 Y(4140)= D s *+ D s *- molecule? Molecule state disfavored. J P =0 + : Γ γγ Br(Y(4140)) →  J/  ) = eV J P =2 + : Γ γγ Br(Y(4140)) →  J/  ) = eV T. Branz et al., PRD80, (2009): if Y is D s *+ D s *- molecule

31 Fit to  J/  invariant mass unbinned maximum likelihood method BW convoluted with Double Gaussian resolution function mass resolution is 5.5 MeV at 4.35 GeV preliminary S.S.=3.9 , const. bkg S.S.=3.2 , linear bkg J P =0 + : Γ γγ Br(X(4350)) →  J/  ) = ± 1.1 eV J P =2 + : Γ γγ Br(X(4350)) →  J/  ) = ± 0.3 eV 825 /fb

32 Preliminary results M(X(4350))= ± 0.7 MeV/c 2 Γ= ± 4.1 MeV/c 2 N (X(4350))= Statistical significance:  Excited P-wave charmonium? Tetraquark? Fl. Stancu, arXiv: D * s D * s0 molecule at 4.34±0.09 GeV? J.R.Zhang et al., arXiv: /fb

33 R values/  states/Y states The Y states should also appear in this plot (between 4.0 and 4.7 GeV!) From PDG } J PC = 1 --  ’,  ’’, Y…

34 Y family (vector states) e + e - →J/ψπ + π - γ ISR e+e - →ψ(2S)π + π - γ ISR Above DD threshold, decay to open charm? PRL 99, (2007)PRL 99, (2007) 550 fb -1 Y(4008) 7σ Y(4260) Y(4360) Y(4660) 6  670 fb -1 arXiv: Y(4260) 454 fb -1 Y(4008) ? M(J/ψππ) M(ψ(2S)ππ) Y(4360) 298 fb -1 Y(4660) ? PRL 98, (2007)

35 Y family  Y(4008), Y(4260), Y(4360), Y(4660) don’t match peaks in D (*) D (*) Xsection  Widths for ψππ transition too large for conventional charmonia  Y(4260) is DD 1 molecule/ccg hybrid? DD 1 [→DD*π] decay should dominate but no signal found D*D*D*D* DD *  (4040)  (4160) Y(4008)  (4415) Y(4660) Y(4260) Y(4350) DD DDπ Λc+Λc–Λc+Λc– ? PRD77,011103(2008) PRL100,062001(2008) PRL98, (2007) PRL101, (2008) e + e - →open charm γ ISR M=4630 Y(4660) ? [hep-ex] DD*π Y(4260) ψ(4415) M(DD*  )

36 What are the Y states? Between 4 and 4.7 GeV, at most 5 states expected (3S, 2D, 4S, 3D, 5S), 7 observed Hybrids are expected in this mass region Molecular states? Cannot rule out threshold effect/FSI/… Y(4260), Y(4360), Y(4660) are all narrow and similar

37 Charged state with hidden charm Z + (4430) and more Unambiguous tetraquark state?

38 Z(4430) ± →ψ(2S)π ±  Found in ψ(2S)π + from B→ψ(2S)π + K. Z parameters from fit to M(ψ(2S)π + )  Confirmed through Dalitz-plot analysis of B→ψ(2S)π + K  B→ψ(2S)π + K amplitude: coherent sum of Breit-Wigner contributions  Models: all known K*→Kπ + resonances only all known K*→Kπ + and Z + →ψ(2S)π +  favored by data  [cu][cd] tetraquark? neutral partner in ψ’π 0 expected  D*D 1 (2420) molecule? should decay to D*D*π PRL100, (2008) PRD80, (2009) Significance: 6.4σ Significance: 6.4σ M 2 (ψ(2S)π + ) M 2 (Kπ + ) K*(890) K 2 *(1430) Z + (4430) M 2 (ψ(2S)π + ) after K* veto 657M BB – ̶̶̶̶̶̶ – ̶̶̶̶̶̶ fit for model with K*’s only – ̶̶̶̶̶̶ – ̶̶̶̶̶̶ fit for model with K*’s and Z

39 Z ± (4430) in BaBar data?  Fits to M(ψ(2S)π + ): no significant Z(4430) signal  M(ψ(2S)π + ) is statistically consistent between BaBar & Belle  Better to have one more experiment to examine it PRD79, (2009) (χ 2 /ndf=54.7/58) M(  (2S)  + ) Belle peak position

40 Two Z ± →χ c1 π ±  Dalitz-plot analysis of B 0 →χ c1 π + K - χ c1 →J/ψγ with 657M BB  Dalitz plot models: known K*→Kπ only K*’s + one Z →χ c1 π ± K*’s + two Z ± states  favored by data M 2 (χ c1 π + ) M 2 (K - π + ) K 2 *(1430) K*(1680) K*(892) K 0 *(1430) K 3 *(1780) ??? M(χ c1 π + ) for 1<M 2 (K - π + )<1.75GeV 2 –̶̶̶̶̶̶ –̶̶̶̶̶̶ fit for model with K*’s –̶̶̶̶̶̶ –̶̶̶̶̶̶ fit for double Z model –̶̶̶̶̶̶ –̶̶̶̶̶̶ Z 1 contribution –̶̶̶̶̶̶ –̶̶̶̶̶̶ Z 2 contribution PRD 78, (2008) Significance: 5.7  Significance: 5.7  Waiting for experiments to confirm them!

41 Search for X/Y states in Y(1S) radiative decays

42 Y(1S)  γX/Y 5.8 fb Y(1S) res. 1.8 fb 9.43 GeV ● σ(e+e-  ψ (2S))=20.2 ±1.1(stat.) pb ● Except for the ISR produced ψ (2S), there are only a few events scattered above the ψ (2S) peak ● No events from J/ ψ sidebands. But one candidate around X(3872) mass region ● B(Y(1S)  γX(3872))B(X(3872)  π + π - J/ψ)<2.2x10 -6 preliminary NEW! ● There are two events scattered above 3.6 GeV. One is at 3.67 GeV, the other is at 4.23 GeV. The orresponding 3π masses are at 0.54 GeV and 1.04 GeV ● B(Y(1S)  γX(3872))B(X(3872)  π + π - π 0 J/ψ)<3.4x10 -6 ● B(Y(1S)  γX(3915))B(X(3915)  ω J/ψ)<3.4x10 -6 preliminary B(Y(1S)  γY(4140))B(Y(4140)   J/ψ)<2.6x10 -6

43 NEW! Y(1S)  γX CJ /η c 5.8 fb Y(1S) res. 1.8 fb 9.43 GeV 5.8 fb Y(1S) res. ● No clear XcJ or η signal is observed ● B(Y(1S)  γX c0 )<5.0x10 -4 ● B(Y(1S)  γX c1 )<1.5x10 -5 ● B(Y(1S)  γX c2 )<1.2x10 -5 ● B(Y(1S)  γ η c )<6.4x10 -5 ● The above upper limits do not contradict with the calculation in K.T.Chao et al.,hep-ph/ For comparison, we also studied: η c  K S Kπ, K+K- π+ π-, 2(π +π-), 2(K+K-) and 3(π +π-)

44 Possible BESIII contribution BESII fine scan 10 years ago ( one of the best cited BES papers ) BESIII will do it (USTC/IHEP group will submit proposal) The Y states should also appear in this plot The X states via decays of excited  s; is the Z + iso-vector? From PDG

45 Summary of the talk Many XYZ states were observed in B-factories and other experiments in XYZ  charmonium + light meson They could be exotic hadrons such as molecular state, tetraquark state, or hybrids or just charmonium states, threshold effect, FSI effect or some other unknown QCD effect. Both theorists and experimentalists should continue work hard and patiently for possibly very rare (even non-existing) exotic hadrons! (Is exotic hadron another ether?) Thanks a lot.

46 backup

47 NameJ PC Γ(MeV) Decay modesExperimentsinterpretation X(3872)1 ++ <2.3  J/ ,  J/ , DD*, … Belle/CDF/D0/BaBar DD* molecule? X(3940)0 ?+ ~37DD* (not DD, ωJ/ ψ ) Belle η c ’’ (?) Y(3940)? ?+ ~30 ω J/ψ (not DD *) Belle/BaBar Y(4140)? ?+ ~11  J/ψ Belle ccss? X(4160)0 ?+ ~140D*D* (not DD, DD*) Belle η c ’’ (?) Y(4008)1 -- ~220  J/  Belle (not Babar) Y(4260)1 -- ~80  J/  BaBar/CLEO/Belle ccg hybrid? X(4350)? ?+ ~13 ,  J/ψ Belle ccss? Y(4360)1 -- ~75  (2S) BaBar/Belle Y(4660)1 -- ~50  (2S), Λ c Λ c (?) Belle Z ± (4430)? ?? ~100ψ(2S)π ± Belle (not Babar) 4-quark? Z ± (4050)?????? ~80χc1π±χc1π± Belle 4-quark? Z ± (4250)?????? ~180χc1π±χc1π± Belle 4-quark? XYZ states charged Z neutral X and Y

48 Shows up in all data subsamples Z(4430)

49 Belle-B A B AR comparison (Z(4430)) Uncorrected data in the K* veto region B A B AR preliminary Both Belle and BABAR data are re-binned (to calculate χ 2 ) and side-band subtracted The BABAR data are normalized (*1.18) to the Belle sample; Luminosity ratio is 1.46 The data distributions are statistically consistent (χ 2 =54.7/58) From J. Brodzicka, LP09

50 BaBar doesn’t see a significant Z(4430) + “For the fit … equivalent to the Belle analysis…we obtain mass & width values that are consistent with theirs,… but only ~1.9  from zero; fixing mass and width increases this to only ~3.1 .” Belle PRL: (4.1 ± 1.0 ± 1.4)x10 -5

51 Compare with PRL results (Z(4430)) Signif: 6.4  Published results Mass & significance similar, width & errors are larger With Z(4430) Without Z(4430) Belle: = ( )x BaBar: No big contradiction K* veto applied

52 Charmonia 2 M(D) recently measured Quantum numbers  (4160)  (4415)  (4040)  (3770) χ c2 ′ ′′ ηc′ηc′ ηcηc J/  χ c2 χ c0 hchc χ c1 n (2S+1) L J n radial quantum number S total spin of qq L relative orbital mom. L = 0, 1, 2 → S, P, D L = 0, 1, 2 → S, P, D J = S + L P = (–1) L+1 parity C = (–1) L+S charge conj. c c Many empty slots to fill Expected broad states decaying to DD, DD*, D*D* All states observed Good agreement with QCD predictions

53  Energy scans by BESII in ‘98-99   Refit of R spectrum: with interferences between ψ 1 -- states Charmonia above DD PLB660, 315 (2008) Many decay channels allowed:  fit complicated  model dependence

54 The Y(2175) at BaBar Babar measured e + e - →  +/0  -/0 and  f 0 (980) observed the Y(2175)   f 0 (980). Phys. Rev. D 76, (2007) M = 2175±10 ±15 MeV  = 58±16 ±20 MeV Y(2175)   f 0 (980) L=232 fb - 1 J/ 

55 Y(2175) in J/    f 0 (980) at BESII Simultaneous fit to signal and sideband events with BW+p3 BES: PRL100, (2008) M = 2186 ± 10 ± 6 MeV  = 65 ± 23 ± 17 MeV B(J/    Y   f 0 (980)   ) =(3.23 ± 0.75 ± 0.73)x10 -4 ~5 

56 M(Y(2175))= 2079  13 MeV  (Y(2175))= 192  23 MeV The Y(2175) at Belle   f 0 (980)     M(  (1680))= 1689  7  10 MeV  (1680))= 211  14  19 MeV Two incoherent BWs fit as central values,  f0(980) fit as one source of error Agree with Babar’s and BES’s measurements Width larger than previous measurements  Y(2175) = excited  remains a possibility Belle: PRD80, (RC) (2009)

57 Combined BaBar+Belle data     1.8  Two incoherent BWs:  2 /ndf=170/111 (C.L.=0.03%!) M(  (1680)) = 1685  5 MeV  (  (1680)) = 208  11 MeV M(Y(2175)) = 2080  12 MeV  (Y(2175)) = 182  20 MeV

58 Combined BaBar+Belle data     2.8  Two coherent BWs:  2 /ndf=158/110 (C.L.=0.19%) M(  (1680)) = 1677  6 MeV  (  (1680)) = 233  16 MeV M(Y(2175)) = 2112  16 MeV  (Y(2175)) = 196  27 MeV

59 Combined BaBar+Belle data  f 0 (980) 2.7 

60 Y(5S) and Y(6S)  Energy scans above Y(4S): Belle: 7.9/fb Babar: 3.9/fb (0.13/fb from CESR)  Motvation: new spectroscopy like in cc?  Babar inclusive: fit to hadronic x-section  Belle exclusive: study of di-pion transitions  Large dipion widths. For other bb: O(keV) Pure bb state or Y b →Y(nS)ππ contributes? PRL100, (2008) arXiv: fit: coherent Y(5S) +Y(6S) fit: coherent Y(5S) +Y(6S) +continuum +continuum Y(nS)ππ x-section [pb] arXiv:  Inclusive and exclusive dipion x-sections inconsistent with PDG Y(5,6S) parameters

61 CLEO PRL 54, 381 (1985)  ( 5S ) Analogy ~ open threshold CLEO: PRL 54, 381 (1985) CUSB: PRL 54, 377 (1985) Y(2175) Y(4260) Y(10890)

62 CLEO PRL 54, 381 (1985)  ( 5S ) CLEO: PRL 54, 381 (1985) CUSB: PRL 54, 377 (1985) We are exploring a mass region with many open-flavor threshold! Constructive interference between amplitudes? Need more study! BES: PRL 88, (2002) What are  (5S),  (4260),  (??)?

63 Is X(3872) a molecule? Simulation by models Production rate in CDF