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Recent Results from BES Weiguo Li IHEP, Beijing Representing BES collaboration ICFP2005

Explore recent findings from BES, including unexpected hadron structures and multiquark candidates. Study on mesons and excited baryon states offers new insights into particle physics mysteries.

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Recent Results from BES Weiguo Li IHEP, Beijing Representing BES collaboration ICFP2005

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  1. Recent Results from BES Weiguo Li IHEP, Beijing Representing BES collaboration ICFP2005 NCU, Chungli, Taiwan Oct. 5, 2005

  2. BESII Detector VC: xy = 100 m TOF: T = 180 ps counter: r= 3 cm MDC: xy = 250 m BSC: E/E= 22 % z = 5.5 cm dE/dx= 8.4 %  = 7.9 mr B field: 0.4 T p/p=1.8(1+p2) z = 2.3 cm Dead time/event: 〈10 ms

  3. Data from BESI and BESII

  4. Recent J/ Results from BESII • Multiquark candidates study at BES * pp threshold enhancement in *observation of X(1835) in * p threshold enhancement in * Kthreshold enhancement in *  enhancement in • Light scalar mesons -- , , f0(980), f0(1370), f0(1500) … • Excited baryon states • Measurements of J/ and c decays

  5. During the past two years, a lot of surprising experimental evidences, including some BES results showed the existence of hadrons that cannot (easily) be explained in the conventional quark model.J/ decay is a good place to search for the new form of hadrons.

  6. Observation of an anomalous enhancement near the threshold of mass spectrum at BES II J/ygpp BES II acceptance weighted BW +3 +5 -10 -25 M=1859 MeV/c2 G < 30 MeV/c2 (90% CL) 0-+ c2/dof=56/56 0 0.1 0.2 0.3 M(pp)-2mp (GeV) 3-body phase space acceptance Phys. Rev. Lett., 91 (2003) 022001

  7. Observation of X(1835) in X(1835) 5.1  X(1835) 6.0  hep-ex/0508025 Accepted by PRL

  8. Combine two channels 7.7 Statistical Significance 7.7  X(1835) BESII Preliminary BESII Preliminary

  9. Refit to J/ pp including FSI M = 1830.6  6.7 MeV  = 0  93 MeV Include FSI curve from A.Sirbirtsev et al.(hep-ph/ 0411386) in the fit (I=0) BES II Preliminary In good agreement with X(1835)

  10. X(1860) from BES has large BR to pp • BES measured: • For a 0-+ meson: • So we would have: Considering that decaying into pp is only from the tail of X(1860) and the phase space is very small, such a BR indicates X(1860) has large coupling to pp !

  11. X(1835) could be the same structure as pp mass threshold enhancement. • It is likely to be a pp bound state since it dominantly decays to pp when its mass is above pp mass threshold. • ’ mode is expected to be the most favorable decay mode for a pp bound state below pp mass threshold G.J. Ding and M.L. Yan, PRC 72 (2005) 015208

  12. Phys. Rev. Lett. 93, 112002 (2004) 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

  13. Similar enhancement also observed in 4 away from phase space.

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

  15. A strong enhancement is observed near the mass threshold of MKat BES II. • Preliminary PWA with various combinations of possible N* and Λ* in the fits —— The structure Nx*has: Mass 1500~1650MeV Width70~110MeV JP favors 1/2- The most important is: BES II Preliminary It has large BR(J/ψ  pNX*) BR(NX* KΛ)2 X 10-4 , suggesting NX* has strong coupling to KΛ.

  16. Observation of  threshold enhancement in J/   DOZI process M3 MKK    BES II Preliminary

  17. BES II Preliminary

  18. A clear threshold enhancement is observed Eff. curve Phase Space BES II Preliminary Side-band S wave fit:

  19. Study of the scalars • There have been hot debates on the existence of  and. • Lattice QCD predicts the 0++ scalar glueball mass in the range 1.5 - 1.7 GeV. f0(1500) and f0(1710) are good candidates.

  20. study  in study  in • studyf0(980), f0(1370), f0(1500), f0(1710) and f0(1790)in 0++

  21. The study of  • evidence for a low mass pole in the early DM2 and BESI data on J/   . • huge event concentration in the I=0 S-wave  channel seen in M~ 500 – 600 MeV in the pp central production exp. • to explain  scattering phase shift data， should be introduced in chiral perturbative theory. • FNAL E791 exp. D++-+ data

  22. The  pole in at BESII 0  M(+-0) M()   M(+-)

  23. Fit to J/→+ (whole mass region) Method I: Channels fitted to the data: J/f2(1270)  f0(980) b1(1235) ’(1450) f2(1565) f2(2240) b1(1235) preliminary f2 contribution f0 contribution

  24. Fit to J/→+ (M < 1.5 GeV) f2 contribution Method II: Channels fitted to the data: J/f2(1270)  f0(980) b1(1235) phase space f0 contribution

  25. Breit-Wigner for :

  26. Fit results: I II Averaged pole position: MeV Phys. Lett. B 598 (2004) 149

  27. The study of  • A possible  pole is controversial. • Some analyses of LASS K scattering data need (800), some don’t. • Scadron et al. favors a nonet made up of , (800), f0(980) and a0(980). • Julich group used t-channel exchanges to explain K scattering data. • evidence of  in FNAL E791 data on D+ K-++ • slightly lower statistics of CLEO D0 K-+0 data find no evidence of  • FOCUS data on K+K-++ require K*0 interfere with either a constant amplitude or a broad 0+ resonance in K

  28. κ hep-ex/0506055 Submitted to PLB

  29. BES Preliminary K*0(1430) 

  30. Pentaquark searches +(1540) • not forbidden by QCD: definite evidence of pentaquark states would be an important addition to our understanding of QCD. • a baryon with S=+1 is a natural candidate

  31. Need more experimental facts(through different processes)BES:e+ e- collision; has relatively clean data samples with less backgroundsinvestigate the pentaquark state  in the hadronic decays of charmonium

  32. y(2S) J/y No pentaquark state (1540) (or ) is observed.

  33. Upper limits @ 90% C.L. PRD70 (2004) 012004

  34. Study of other scalars • Lattice QCD: • the lightest scalar glueball in the region of 1.5- 1.7 GeV • Glueball searches should be performed in • simultaneously. • I will skip the other parts of J/ decay results to save time, please refer to the BES talks at Hadron05.

  35. BES preliminary c0→+K+K (2S) and CJ Decays • Different way for scalar study: • Start from JPC=0++, 1++, 2++ • Start from gluon+gluon • Pair production of scalars, very different information than in J/ decays • Can study different kinds of resonances: • (    )(K  K ) • (K    )(K    ) • (K  ) K c0 1371 evts c1 c2 hep-ex/0508050 Submitted to PRD

  36. BES preliminary,c0→+K+K (+ ) (K+K ) f0(980) f0(980) f0(2200) f0(1710) f0(1370) (770) Q. Zhao, hep-ph/0508086, try to understand these data and the scalars …

  37. (K  )(K  ) BES preliminary c0→+K+K With kappa-kappa K*(892)0 K*0/2(1430) K*0(1950) Without kappa-kappa S=39.

  38. (K  )K BES preliminary, c0→+K+K 1371 events K1(1270) K1(1400) K1(1270) M(K) [896±60] K1(1270) The mixing angle between K1A and K1B>57 degrees, while in ’ decays to K1K, the angle is <29 degrees. Why? M() [700,850]

  39. “12% rule”and“ puzzle” • Violation found by Mark-II , confirmed by BESI at higher sensitivity. • Extensively studied by BESII/CLEOc • VP mode:  , K*+K-+c.c., K*0K0+c.c., 0,… • PP mode: KSKL • BB mode: pp, , … • VT mode: K*K*2, f2’, a2, f2 • 3-body: pp0, pp, +-0, … • Multi-body: KSKShh, +-0 K+K- , 3(+-), … MARK-II K*K ρπ

  40. Extension of the “12% rule” • In Potential model, if J/, ’, and ’’ are pure 1S, 2S, and 1D states, one expects • but ’ and ’’ are known not pure 2S and 1D states, PRD17, 3090 (1978); 21, 203 (1980); 41, 155(1990); … • Let’s look at data … (and first, the story of )

  41. ’ + - 0 BESII: PLB619, 247 (2005) CLEOc: PRL94, 012005 (2005) 2290s 1960s BESII CLEOc BES and CLEOc in good agreement!

  42. ’ + - 0 Dalitz plots after applying 0 mass cut! Very different from J/3! CLEOc BESII J/ Similar Dalitz plots, different data handling techniques: PWA vs counting! ’ is observed, it is not completely missing, BR is at 10-5 level!

  43. J/ + - 0 Make  mass cut, and count events PWA analysis assuming  interferes with excited  states L. P. Chen and W. Dunwoodie, Hadron’91, MRK3 data PDG: 1.270.09% Very different!

  44. ’’ + - 0 Very small in ’’ decays φ phase interference interference • Continuum contribution is crucial in ’’ analysis: • Total ’’ charmless decays (<2nb) is much less than total continuum process (~16nb), • Interference between amplitudes BESII preliminary

  45. ’’ + - 0 BESII: hep-ex/0507092 CLEOc: CLEO-CONF 05-01 BESII preliminary CLEOc preliminary 3.773GeV 3.650GeV 3.773GeV 3.670GeV BES and CLEOc are in good agreement! X-section at ’’ peak is smaller than at continuum!

  46. BESII: hep-ex/0507092 CLEOc: CLEO-CONF 05-01 ’’ + - 0 BESII preliminary CLEOc preliminary 3.773 3.65 3.773 3.67 Subtle difference in handling efficiency and ISR correction. BES and CLEOc are in good agreement! X-section at ’’ peak is smaller than at continuum! non-zero ’’ amplitude.

  47. BESII: hep-ex/0507092 CLEOc: CLEO-CONF 05-01 ’’  Wang, Yuan and Mo:PLB574,41(2003) Total cross section Three unknowns with two equations --- One can plot the BR versus phase . B depends on efficiency and ISR correction, efficiency and ISR correction depends on B(s) ! Iteration is necessary!

  48. BESII: hep-ex/0507092 CLEOc: CLEO-CONF 05-01 ’’  BES data restrict BR and phase in a wide range (@90% C.L.): CLEOc data further restrict BR and phase in a ring*. At =-90: *Toy MC is used to get BR from CLEOc data (not CLEO official results)!

  49. J/ , ’ , ’’  ρπ • Partial width of ψ’’ρπ is larger than that of ψ’ρπ! • hard to understand if ψ’’ is pure 1D state, also hard if ψ’’ is 2S and 1D mixture. In S-D mixing model, using mixing angle θ=12°, using Rosner’s assumption (12% rule for 1S and 2S), one predicts Q’ρπ =(2.7-5.3)% ! -90 or imperfect model?

  50. Other ’ decay modes • ’    is suppressed by a factor of 60! • ’’    is enhanced! • Other modes may supply more information! We list a few new measurements using BESII/CLEOc data …

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