1 / 34

Pentaquark search and other multiquark candidates at BES

Pentaquark search and other multiquark candidates at BES. Xiaoyan SHEN Representing BES Collaboration Institute of High Energy Physics, CAS shenxy@ihep.ac.cn ICHEP 2004 August 16 - 22, 2004, Beijing, P. R. China. Outline. Introduction Pentaquark searches at BES

renee-roth
Download Presentation

Pentaquark search and other multiquark candidates at BES

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Pentaquark search and other multiquark candidates at BES Xiaoyan SHEN Representing BES Collaboration Institute of High Energy Physics, CAS shenxy@ihep.ac.cn ICHEP 2004 August 16 - 22, 2004, Beijing, P. R. China

  2. Outline • Introduction • Pentaquark searches at BES • Other multiquark candidates at BES *pp threshold enhancement in * p threshold enhancement in * Kthreshold enhancement in • Summary

  3. Introduction World J/ and (2S) Samples (×106) BESII Detector BESII 58MJ/ J/ BESII 14M(2S) • VC: xy = 100 m TOF: T = 180 ps • MDC: xy = 220 m BSC: E/E= 21 % • dE/dx= 8.5 %  = 7.9 mr • p/p=1.78(1+p2) z = 2.3 cm • counter: r= 3 cm B field: 0.4 T z = 5.5 cm (2S)

  4. Pentaquark searches at BES +(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

  5. experimental status of +(1540) • “Positive” experiments: • many • “Negative” experiments: • many • BES: • ALEPH: RΛ*(1520) < 0.1 • DELPHI: • L3: • HERA-B: RΛ*(1520) < 0.02 • SPHINX: RΛ*(1520) < 0.02 • CDF: (LEPS) MΘ

  6. 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

  7. y(2S)  KSpK-n and KSpK+nDecays pentaquark  NK NK

  8. J/y KSpK-n and KSpK+nDecays

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

  10. Upper limits @ 90% C.L.

  11. Upper limits @ 90% C.L.

  12. Multiquark candidates at BES 1.Near pp threshold enhancement in enhancement c Phys. Rev. Lett., 91 (2003) 022001

  13. Fit results Fitted peak J/ygpp BES II +3 +5 -10 -25 Mass: M=1859 MeV/c2 Width: G < 30 MeV/c2 (90% CL) Fitted curve c2/dof=56/56 0 0.1 0.2 0.3 M(pp)-2mp (GeV) Eff. curve BG curve

  14. MARK-III & DM2 Results MARK-III Threshold enhancement DM2 Claimed in Phys. Rep. 174(1989) 67-227 Too small statistics to draw any conclusion on the threshold enhancement, e.g., cannot exclude known particles such as h(1760)

  15. Belle sees low-mass pp systems in B decays BppK BD0pp M pp (GeV) M pp Statistics is also low.

  16. This enhancement is important: • FSI not favored • mass≤2mp，width is narrow  Hard to be explained as a conventional qq meson

  17. pp bound state (baryonium)? There is lots & lots of literature about this possibility deuteron: baryonium: attractive nuclear force attractive force? + n + - loosely bound 3-q 3-q color singlets with Md = 2mp- e loosely bound 3-q 3-q color singlets with Mb = 2mp-d ? Observations of this structure in other decay modes are desirable.

  18. 2. Observation of an enhancement near mass threshold in process  Data/MC The clear Λ signal in data shows high purity of signal.

  19. Phase Space Data Data

  20. S-wave BW fit results P-wave BW fit results • M = (2075 12  5) MeV Γ = (90  35  9) MeV BR = (5.9  1.4  2.0) 10-5 • M = (2044 17) MeV • Γ = (20  45) MeV • 2/d.o.f = 32.5/26 • 2/d.o.f = 31.1/26 • About 7σ statistical significance high L hypotheses fail The systematic errors are carefully studied in S-wave case. Accepted by P. R. L. Hep-ex/0405050

  21. Near threshold enhancement is also observed in Fix the parameters, 4 away from phase space. Accepted by P. R. L. Hep-ex/0405050

  22. 3. Near threshold enhancement in Nx Nx Events/10MeV (Arbitrary normalization) PS, eff. corrected Nx

  23. PWA is performed to • possible N* and *states listed in PDG are fitted • N(1720), N(1900), (1520), (1690), … • manydifferent combinations are tried • different form factors are used • different JP of Nx is tried • also tried N(1535) to fit Nx

  24. N(1720), N(1900), (1520), (1690) …. included in the PWA fit An example: • Mass and Width scan M  1520 – 1620 MeV   110 MeV • JP = 1/2- • Total fit (S=-952) • Nevent: Fraction Nevent NX 22% 1210 Mass scan(GeV/c2) Ln L Width scan(GeV/c2)

  25. Events/10MeV Crosses: data Hist.: PWA fit projection Dalitz plot (MC) Dalitz plot (data)

  26. JP check with various combinations  • JP½- ½+ 3/2- 3/2+ non • A -940 -848 -848 -930 -813 • B -845 -783 -806 -833 -752 • C -952 -841 -844 -916 -768 • D -880 -768 -752 -822 -650 • E -957 -889 -893 -944 -875 • F -970 -920 -925 -963 -919 • G -954 -925 -919 -944 -909

  27. fit results

  28. An abnormal enhancement is observed in the mass threshold of MK • Its mass and width: (large uncertainty near threshold, high statistics is crucial!) Mass 1500~1650MeV Width70~110MeV JP favors 1/2- • large BR(J/pNx)Br(NxK) (2*10-4). What is it?? Possibly N*(1535) with large coupling to K Kmolecular state ??

  29. Summary • no (1540) seen in both J/ and (2S) hadronic decays. • a near pp threshold enhancement observed in J/pp decay. Baryonium?? • a near p threshold enhancement observed in both J/ pK and (2S) pK decays. • a near K threshold enhancement observed in J/pK. large coupling to K. K molecular state??

  30. Thank you! 谢谢！

  31. FSI ? —— Not favored • Theoretical calculation (Zou and Chiang, PRD69 034004 (2003))shows that the enhancement caused by one-pion-exchange FSI is too small to explain the BES structure. • For FSI, the BES structure should be the same as in elastic scattering (Bugg, hep-ph/0406293): But it is NOT ! The enhancement caused by Coulomb interaction is even smaller than one-pion-exchange FSI ! |M|2 BES BES |M|2 Both arbitrary normalization Both arbitrary normalization one-pion-exchange FSI

  32. NO strong threshold enhancement in collision (at LEAR) • 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 ! |M|2 |M|2 BES BES Both arbitrary normalization Both arbitrary normalization

  33. Any inconsistency? NO! • For example: with Mres = 1859 MeV, Γ = 30 MeV, J=0, BR(ppbar) ~ 10%, based on: At Ecm = 2mp + 6 MeV ( i.e., pLab = 150 MeV ), in elastic process, the resonant cross section is only~ 0.6 mb : much smaller than the continuum cross section ~ 94 +/- 20 mb  Very difficult to observe it in collisions.

  34. PWA of the near-threshold enhancement(NX) in mK PWA with: • a: NX,N(1720),N(1900),(1520), (1570), (1690), (1810), X(2075) • b: NX,N(1720),N(1900)，(1520), (1690), (1810), X(2075) • c: NX,N(1720),N(1900),(1520), (1570), (1690), (1890),X(2075) • d: NX,N(1720),N(1900),(1520), (1690), (1890),X(2075) • e: NX,N(1720),N(1900),(1520), (1570), (1690), (1810), (1890),X(2075) • f: NX,N(1720),N(1900),N(2050), (1520), (1570), (1690), (1810), (1890),X(2075) • g: NX,N(1720),N(1900),N(2050), (1520), (1570), (1690), (1810), (1890) J(p) 1/2(-) 3/2(+) 3/2(+) 3/2(+) 3/2(-) 1/2(-) 3/2(-) 1/2(+) 3/2(+) 1(-) m(GeV)1.535,1.720, 1.900, 2.050, 1.5195, 1.570, 1.690, 1.810, 1.890, 2.080 (GeV) 0.150, 0.150 0.300, 0.200, 0.0156, 0.070, 0.060, 0.150, 0.100, 0.080 • h:N(1535),N(1650),N(1720),N(1900), (1520), (1570),(1690), (1810), (1890),X(2075) • i: N(1535),N(1650),N(1720),N(1900), (1520), (1690), (1810), (1890),X(2075) J(p)1/2(-) 1/2(-), mN(1650)=1.650, N(1650)=0.150 • j: 18Res All possible N* and *states listed in PDG and N(1900)(3/2-),N(2050)(1/2+,3/2+), (1570), X(2075) N(1535）=NX

More Related