New Results on Hadron Spectroscopy (Experimental Review) Shan JIN Institute of High Energy Physics (IHEP) Chinese Academy of Sciences August 20, 2004 ICHEP 2004, Beijing

Multi-quark State, Glueball and Hybrid  Hadrons consist of 2 or 3 quarks ： Naive Quark Model ：  New forms of hadrons: Multi-quark states ： Number of quarks > ＝ 4 Hybrids ： qqg ， qqqg … Glueballs ： gg ， ggg … Meson （ q q ） Baryon （ q q q ）

Multi-quark states, glueballs and hybrids have been searched for experimentally for a very long time, but none is established. However, during the past one year, a lot of surprising experimental evidences showed the existence of hadrons that cannot (easily) be explained in the conventional quark model.

There are so many exciting unexpected new observations as well as many negative search results that I will not be able to cover many “conventional” topics, such as charm baryons, charmonium production… I would deeply apologize to those experiments who contribute these beautiful results to the conference.

Outline  Multi-quark candidates: Pentaquarks X(3872) D sJ (2632) Resonant structures near mass thresholds and  J/  mass thresholds.  Light scalar mesons: σ, κ, f 0 (980), f 0 (1370), f 0 (1500), f 0 (1710), f 0 (1790)  Other interesting results from BES and CLEO-c

Observations of pentaquarks

Θ + (1540)  First evidence of pentaquark was presented by LEPS in the process : N event = 19 +/- 2.8 Significance: ~ 4.6 σ  Minimum quark content: uudds Its mass and width are consistent with chiral soliton model prediction. M nK + LEPS at 90% CL

CLAS M(nK + ) CLAS

SAPHIR M(nK + ) (fit)

M(pK s ) Inclusive γ*- production HERMES

Fragmentation ZEUS (fit)  R Λ ~ 0.04 Assuming the production rate of Λ*(1520) is 5 times smaller than Λ, I estimated: R Λ*(1520) ~ 0.2 M(pK s )

Asratyan et al. - induced DIANA M(pK s )

Pentaquarks at JINR How many pentaquarks did they see? M(nK + )

(LEPS) MΘMΘ F. Close and Q. Zhao, hep-ph/

ΓΘΓΘ  PDG 04: (R.N. Cahn, G.H.Trilling, PR D R, based on the production cross-section estimation from DIANA data, σ R =AB i B f Γ)  Consistent with other estimation of the upper limit on the width based on K + N partial wave reanalysis ( < 1 MeV ) Why the width is so narrow seems very hard to understand.

Isospin of Θ + (1540)  No Θ ++ was observed by SAPHIR, HERMES or other experiments.  Θ + is an isoscalar

Ξ -- (1862)  Also evidence for Ξ 0 (1862) ( I = 3/2 ) NA49 pp collision at E cm =17.2GeV

Θ c (3099)  Minimum quark content: uuddc DIS (Q 2 > 1GeV 2 ) Poisson Prob.

Negative search results on pentaquarks

BES Upper 90% C.L. BR (  (2S)     (K S p)(K - n) + (K S p)(K + n)) < 0.84X10 -5 BR ( J/      (K S p)(K - n) + (K S p)(K + n)) < 1.1 X10 -5  (2S)J/  R Λ*(1520) < ?

ALEPH  No evidence for Θ + (1540), Ξ -- (1862), Ξ 0 (1862), Θ c (3100) in Z decays M(pK s )

Also no evidence for Θ + (1540), Θ ++ (1540) at DELPHI ALEPH Limits at 95% C.L.

 No evidence for Θ + (1540) in two photon collisions. L3

CDF  No evidence of Θ + (1540), Ξ -- (1862), Ξ 0 (1862) or Θ c (3100) observed at CDF. M(pK s ) Θ c (3100) Θ + (1540)

HERA-B M(pK s ) No evidence of Θ + (1540), Ξ -- (1862), Ξ 0 (1862) at HERA-B (proton-nucleus collisions at )

 Θ c (3099) was not observed at ZEUS in a data sample which is 1.7 times of the H1 data sample. M(D*p) 95% C.L. upper limit: Inconsistent with H1: ~0.01 ZEUS More quantitative comparisons require detector efficiency corrections.

BaBar  No evidence of Θ + (1540), Ξ -- (1862) or other possible pentaquarks was observed at BaBar. Upper limits were set.  R Λ*(1520) < ~ 90 % CL

Belle  Belle did not see Θ + (1540): R Λ*(1520) < 90 % CL  Θ c (3100) was not seen either. 155fb -1  (1520) nothing m(GeV) pK - pK S

Inconsistencies (I)  Width of Θ + (1540) Two “positive” experiments: HERMES: Γ Θ = 17  9  2 MeV ZEUS: Γ Θ = 8  4 MeV K + N PWA results indicates Γ Θ < 1 MeV  Mass of Θ + (1540)

(LEPS) MΘMΘ

Inconsistencies (II)  Production rate (e.g. for Θ + (1540) ) “Positive” experiments: SAPHIR: R Λ*(1520) ~ 0.3 HERMES: R Λ*(1520) ~ 1.6~3.5 ZEUS: R Λ*(1520) ~ 0.2 ( I estimated from R Λ ~ 0.04 ) SVD-2: R Λ*(1520) > 0.2 ( estimated by SPHINX, hep-ex/ ) “Negative” experiments: ALEPH: R Λ*(1520) < 0.1 BaBar: R Λ*(1520) < ~ 0.01 Belle: <0.02 HERA-B: R Λ*(1520) < 0.027~0.16 SPHINX: R Λ*(1520) < 0.02

 The “negative” experiments have much larger statistics, also are at relatively higher energies (but Babar and Belle are at low energy). Pentaquarks do not exist, or Pentaquarks have very exotic production mechanism. via N*? Then why N* has much higher production rate at low energy?  Looking forward to more experimental results at low energy with high statistics, especially those photo-production experiments !

Comments on statistical significance  Using to estimate statistical significance seems too optimistic. Even if we have firm knowledge on the background  CL b as LEP Higgs used is recommended.  When the background is estimated from the fit of sideband, the likelihood ratio with D.O.F. taken into consideration is a better estimator of statistical significance. In this case, the uncertainty of all possible background shapes should be included in the uncertainty of significance.  Do not optimize/tune the cuts on the data! Determine the cuts based on MC optimization before looking at data. The sys. uncertainty on significance from “bias” cut is hard to estimate.  “Look elsewhere” effect may reduce the significance by 1~2σ.

X(3872)

First observed by Belle Experiments in:

M(      J/   ) – M(J/   )  ’   J/  X(3872) 10σ effect Belle at 90% C.L.

X(3872) at CDF and D0 5.2  effect 11.6  effect

X(3872) at BaBar  The significance is low (about 3.5 σ), but its production rate is consistent with Belle: 3.5 σ effect BaBar

 No evidence of X   is observed in B 0  X  K +, B   X  K 0 s with X    J/   -  0.  So, isovector hypothesis of X   disfavored. Search for B  X   K at BaBar Mode B   J/    0 K + B   J/    0 K 0 s n obs n bkg ± ± 6.2 n signal ± ± %CL < 5.8 x < 11 x 10 -6

CLEO – γγFusion and ISR (90% C.L) Consistent with Yuan et al. estimation from BES data: J PC =1 - - disfavoured

New decay mode observed at Belle  Belle observed a new decay mode of X(3872)   *J/    +  -  0 J/    (X   J/  )/  (X      J/  ) = 0.8 ±0.3± 0.1 M(       ) M(J/        ) B  K X(3872) N evt =10.0 ± 3.6 Signif = 5.8 

No other decay modes of X(3872) are observed  So far, it is only observed in  J/  and  *J/  modes. 90% C.L. upper limits (most from Belle):  Non-observation of DD modes suggests that J P =0 +, 1 -, 2 +,…, is ruled out. BaBar

Is X(3872) a Charmonium?  All possible charmonium assignments seem to have difficulties (S.L. Olsen, hep-ex/ ): StatenicknameJ PC comment 1 3 D 2 ψ2ψ Mass wrong; Г γχc1 too small 2 1 P 1 h’ c 1 +- Ruled out by |cosθ J/ψ | distribution 1 3 D 3 ψ3ψ Mass & width wrong; Г γχc2 too small; Spin is too high 2 3 P 1 χ ’ c Г γJ/ψ too small 11D211D2 η c B(π + π - J/ψ ) expected to be very small 3 1 S 0 η”cη”c 0 -+ Mass and width are wrong

DD* “Molecular State”?  M X(3872) is very close to M D + M D*.  It was suggested that a DD* multi-quark “molecular state” have large BR(X  D 0 D 0  0 ). Belle observes: Some theoretical calculations predict the above ratio is small. (Swanson’s talk in Session 10)  Swanson also predicts: Consistent with Belle new observation. at 90% C.L.

D sJ (2632)

D sJ (2317) and D sJ (2460) BaBar - D sJ (2317) CLEOBelle D SJ (2317) D SJ (2460) D SJ (2317) D SJ (2460)

D SJ (2632) at SELEX  A narrow resonance was observed in mode.  N event = 45.0  9.3  The significance is about 7.2 σ using. Probability of 6 bins region with > 100 events anywhere on this plot with background of 54.4+/-2.5: 3x10 -6  ~4.6σ (Talk given by P.S. Cooper at PIC 2004) D sJ (2632)

 D SJ (2632) was also observed in D 0 K + mode.  N event = 14.0  4.5  The significance is about 5.3 σ (?) using.

Properties of D SJ (2632)  Mass:  1.6 MeV ( above D (*) K threshold )  Narrow Width: < 17 MeV at 90% C.L.  Unusual decay pattern: What is it? First radial excitation of DS*(2112)? A csg hybrid? A tetraquark or molecular state? ( Y.Q. Chen and X.Q. Li, hep-ph/ ; K.T. Chao, hep-ph/ ; T. Barnes et al., hep-ph/ ; Y.R. Liu et al., hep-ph/ … )  Next talk

D SJ (2632) search at CLEO  SELEX noted one-bin excess at 2636 MeV in CLEO 2.16 fb -1 data.  However, CLEO did not observe a narrow peak around 2632 MeV in 20 fb -1 data. D sJ (2632) ?

D sJ (2632) + Events/10 MeV/c 2 D SJ (2632) search at BaBar BaBar did not see D SJ (2632) in the same decay modes as SELEX in 125 fb -1 data.

 D sJ (2632) B (D sJ (2632))  D 0 K)  D sJ (2573) B(D sJ (2573))  D 0 K) < Known state D sJ (2573) is clearly seen (N=7292  164) but no sign of D sJ (2632) (N=-66  64) D sJ (2632) N/ 2MeV D 0 K + mass D s  mode under study cf. SELEX 56  27% 550  M(MeV) 850 SELEX D SJ (2632) search at Belle 155fb -1 Belle

Resonant structures near, KΛ mass thresholds and  J/  mass thresholds

Observation of an anomalous enhancement near the threshold of mass spectrum at BES II M=1859 MeV/c 2  < 30 MeV/c 2 (90% CL) J/    pp M(pp)-2m p (GeV) body phase space acceptance  2 /dof=56/56 acceptance weighted BW  10  25 BES II

 With threshold kinematic contributions removed, there are very smooth threshold enhancements in elastic “matrix element” and very small enhancement in annihilation “matrix element”:  much weaker than what BES observed ! NO strong dynamical threshold enhancement in cross sections (at LEAR) |M| 2 BES Both arbitrary normalization

Any inconsistency? NO!  For example: with M res = 1859 MeV, Γ = 30 MeV, J=0, BR(ppbar) ~ 10%, an estimation based on: At E cm = 2m p + 6 MeV ( i.e., p Lab = 150 MeV ), in elastic process, the resonant cross section is ~ 0.6 mb : much smaller than the continuum cross section ~ 94  20 mb.  D ifficult to observe it in cross sections.

Why can it be seen in J/  decays, but not in cross sections?  Reason is simple: J/  decays do not suffer large t-channel “background”.  It is an s-channel effect ! >>

Final State Interaction ? —— Not favored 1.Theoretical calculation (Zou and Chiang, PRD (2003)) shows: The enhancement caused by one-pion-exchange (OPE) FSI is too small to explain the BES structure. 2.The enhancement caused by Coulomb interaction is even smaller than one-pion-exchange FSI ! BES one-pion-exchange FSI |M| 2 Both arbitrary normalization BES Both arbitrary normalization Coulomb interaction

Final State Interaction ? —— Not favored Theoretical calculation might be unreliable, however, according to Watson’s theorem, we can use elastic scattering experiments to check the FSI effect, i.e., if the BES structure were from FSI, it should be the same as in elastic scattering : But it is NOT !  FSI cannot explain the BES structure. elastic scattering |M| 2 BES Both arbitrary normalization

pp bound state (baryonium)? + n+  deuteron: loosely bound 3-q 3-q color singlets with M d = 2m p -  baryonium: loosely bound 3-q 3-q color singlets with M b = 2m p -  ? attractive nuclear force attractive force? There is lots & lots of literature about this possibility E. Fermi, C.N. Yang, Phys. Rev. 76, 1739 (1949) … I.S. Sharpiro, Phys. Rept. 35, 129 (1978) C.B. Dover, M. Goldhaber, PRD 15, 1997 (1977) … A.Datta, P.J. O’Donnell, PLB 567, 273 (2003)] M.L. Yan et al., hep-ph/ Observations of this structure in other decay modes are desirable.

Observation of an anomalous enhancement near the threshold of mass spectrum at BES II BES II 3-body phase space For a S-wave BW fit: M = 2075  12  5 MeV Γ = 90  35  9 MeV

PS, eff. corrected Observation of a strong enhancement near the threshold of mass spectrum at BES II (Arbitrary normalization) BES II NX*NX*

 A strong enhancement is observed near the mass threshold of M K  at BES II.  Preliminary PWA with various combinations of possible N* and Λ* in the fits —— The structure N x *has: Mass 1500~1650MeV Width 70~110MeV J P favors 1/2 -  consistent with N*(1535) The most important is: It has large BR(J/ψ  pN X *) BR(N X *  KΛ)  2 X 10 -4, suggesting N X *has strong coupling to KΛ. indicating it could be a KΛ molecular state (5 - quark system). cf: f 0 (980)

 Fit with BW: Observation of an anomalous enhancement near the threshold of mass spectrum at Belle Belle

 If it is fit with a BW:  Significance: > 8  Observation of an anomalous enhancement near the threshold of  J/  mass spectrum at Belle Belle B  K  J/ 

Threshold Enhancements in J/  decays and B decays  They may come from different mechanism: There is “fragmentation” mechanism in B decays but NOT in J/  decays. Belle BES II “Threshold” enhancement in B decays is much wider and is not really at threshold. It can be explained by fragmentation mechanism. Threshold enhancement in J/  decays is obviously much more narrow and just at threshold, and it cannot be explained by fragmentation mechanism.

Is the STRONG threshold enhancement universal in J/  decays ? —— NO !  Actually in many other cases we do NOT see STRONG threshold enhancements !  For example: In J/  decays at BES II

Light Scalar Mesons: σ, κ, f 0 (980), f 0 (1370), f 0 (1500), f 0 (1710), f 0 (1790)

Why light scalar mesons are interesting?  There have been hot debates on the existence of σ and κ.  σ, κ and f 0 (980) are also possible mutiquark states. They are all near threshold.  Lattice QCD predicts the 0 ++ scalar glueball mass ~ 1.6 GeV. f 0 (1500) and f 0 (1710) are good candidates.

σ at BES  BES II observed σ in J/    +  -.  Pole position from PWA: BES II

 BES II observed  in J/  K*K  K  K .  Preliminary PWA result Pole position: κ at BES BES II Preliminary

 Important parameters from PWA fit:  Large coupling with KK indicates big component in f 0 (980) BES II Preliminary f 0 (980) at BES f 0 (980)

 f 0 (980) is observed in    f 0 (980)    at KLOE (Background: ISR, FSR and  ).  The results support that f 0 (980) has large coupling with KK. f 0 (980) at KLOE KLOE Preliminary f 0 (980) Background subtracted

 There has been some debate whether f 0 (1370) exist or not.  f 0 (1370) clearly seen in J/   , but not seen in J/   . BES II Preliminary PWA 0 ++ components f 0 (1370) NO f 0 (1370) f 0 (1370) at BES

 Clear f 0 (1710) peak in J/    KK.  No f 0 (1710) observed in J/    ! f 0 (1710) at BES BES II Preliminary f 0 (1710) NO f 0 (1710)

 ZEUS observed a narrow peak around 1730 MeV in K S K S mode:  Its width is much narrower than BES and others. Spin-parity needed.  How many mesons in this mass range? f 0 (1710) (?) at ZEUS f 0 (1710) ???

 A clear peak around 1790 MeV is observed in J/   .  No evident peak in J/    KK. If f 0 (1790) were the same as f 0 (1710), we would have: Inconsistent with what we observed in J/   ,  KK New f 0 (1790) at BES BES II Preliminary f 0 (1790) ?  f 0 (1790) is a new scalar !

Scalars in J/   ,  KK  Two scalars in J/    : One is around 1470 MeV, may be f 0 (1500)? The other is around 1765 MeV, is it f 0 (1790) or a mixture of f 0 (1710) and f 0 (1790)?  One scalar f 0 (1710) in J/    KK. BES II Preliminary

f 0 (1500) at BES  One scalar with a mass = 1466  6  16 MeV is needed in J/   , is it f 0 (1500)? Why the mass is different from PDG?  No peak directly seen in ,  KK, ,  KK.

OZI rule and flavor tagging in J/  hadronic decays  In J/  hadronic decays, an  or Φ signal determines the or component, respectively.  OZI rule

Unusual properties of f 0 (1370), f 0 (1710) and f 0 (1790)  f 0 (1710): It dominantly decays to KK (not to  )  It is mainly produced together with  (not  )  What is it ?  f 0 (1370) and f 0 (1790) They dominantly decays to  (not to KK)  It is mainly produced together with  (not  )  What are they ?  Scalar Puzzle

Other interesting results from BES and CLEO-c

Possible new N*(2050) at BES II N*(1440)? N*(1520) N*(1535) N*(1650) N*(1675) N*(1680) ? BES II Preliminary

 decays and 12% rule test  Puzzle: Q h <<12%   VP Most channels BRs are consistent. BES BR(  ) > CLEO by ~ 3 , because PWA takes into acount the interference. BR(K* 0 K 0 ) are deviated

CLEO-c

Summary  Pentaquarks need confirmation, then we need to answer: The exotic production mechanism of pentaquarks. Why the widths are so narrow? What are their J P ?  One new decay mode X(3872)   *J/  is observed at Belle. We still need to: Find more decay modes of X(3872) Understand its nature: a charmonium or molecular state?  D sJ (2632) needs confirmation, then we need to understand its width and unusual decay properties, also its unusual production mechanism.

 A unique very narrow threshold enhancement is observed in decays at BES II: It is not observed in elastic cross section  it cannot be explained by FSI. It is obviously different from the structure observed in B decays and it cannot be explained by fragmentation.  We need to understand the nature of the strong anomalous baryon-antibaryon, baryon-meson threshold enhancements in J/  decays: multiquark states or other dynamical mechanism ? (keeping in mind that there are no strong threshold enhancements in many cases)  We need to understand the Scalar Puzzle: why many scalar mesons behave differently in the production and decay properties? We also need to answer: How will the new observed f 0 (1790) change the scalar glueball picture?

 No matter what are the interpretations for the recent new surprising observations, these discoveries certainly open a new window for understanding the strong interaction and hadron spectroscopy.  We need to have a global picture if there are new forms of hadrons beyond the naïve quark model —— any pentaquark, tetraquark, molecular state or other multiquark states cannot stay alone ! A lot of opportunities for BES III and other experiments working on hadron spectroscopy !!! Prospects

谢 谢！ Thank You!

ZEUS  No evidence for Ξ -- (1862), Ξ 0 (1862) in deep inelastic scattering data.

WA89  Ξ - - (1862) was searched for with Ξ - candidates at WA89.  No evidence 99.9% C.L. hep-ex/

SPHINX  SPHINX systematically searched for Θ + (1540) in many final states.  No evidence was observed. R Λ*(1520) 90 %CL Cross Section Limit vs. M(NK) hep-ex/

MARK-III & DM2 Results Threshold enhancement Claimed in Phys. Rep. 174(1989) Too small statistics to draw any conclusion on the threshold enhancement, e.g., cannot exclude known particles such as  (1760) MARK-III DM2