1. Nstars: Open Questions Nstars: Open Questions L. Tiator, Institut für Kernphysik, Universität Mainz  Introduction  Roper and S 11  the role of the D 15 or P 11 pentaquark in eta production  missing resonances in etaprime and kaon production  Summary and Conclusion

2. MAID collaboration Dieter Drechsel and L.T. Institut für Kernphysik, Universität Mainz, Germany Sabit Kamalov Laboratory of Theoretical Physics, JINR, Dubna, Russia Wen-Tai Chiang and Shin Nan Yang (for  and  ‘) Physics Department, National Taiwan University, Taipei, Taiwan Terry Mart (for  ) Departemen Fisika, FMIPA, Universitas Indonesia, Depok, Indonesia

3. What is a resonance? What is a resonance? - a peak in the cross section

7. What is a resonance? What is a resonance? - a peak in the cross section - a peak in the imaginary part of a pw amplitude associated with a zero in the real part

8. P 33 partial wave W=1232 MeV S 11 partial wave W=1535 MeV no zero crossing for S 11 (1535) it works for the  (1232) pw amplitudes of pion photoproduction

9. What is a resonance? What is a resonance? - a peak in the cross section - a peak in the imaginary part of a pw amplitude associated with a zero in the real part - a pole of the T-matrix in the 2nd Riemann sheet e.g. with speed-plots of pw amplitudes

11.  Argand Diagrams and Speed-Plots

12. What is the origin of a resonance? What is the origin of a resonance? - a (qqq) bound or excited state with possible admixtures of (qqqg) or (qqq qq) etc. - a dynamically generated object of nucleon + meson interaction, e.g.:   (1232) = N +  does not work P 11 (1440) = N +  may work well (e.g. Krewald et al) (but e.m. properties are not yet tested) S 11 (1535) =  +  also works in some cases (Waas, Weise, Kaiser) (cannot describe n/p ratio, also form factors would be a real test) - M. Lutz (GSI): all resonances, except  (1232), can be dynamically generated)

13. How can resonances be tested? - mass, width, pole position and hadronic decay modes (branching ratios) in different channels - e.m. transition moments or photon couplings - e.m. transition form factors

15. 4 missing resonances in the gap 1800 MeV < W < 1900 MeV

17. open questions for  Roper and S 11 resonances photon couplings of most resonances are still quite inaccurate, even for 4-star D 13 partial wave has ambigous solutions below the resonance

18. comparison between MAID and SAID

19. SAID MAID

20. comparison between MAID and SAID

21. current situation with the P 11 (Roper) multipoles W=1440 MeV W=1710 MeV

26. CB proposal with MAMI C

27. open questions for  qqq resonances vs. dynamically generated resonances with  N or with , e.g. S 11 (1535) target asymmetry in S 11 /D 13 region exotic resonances: Does the  + pentaquark exist? if so, it should have a non-strange partner P 11 (~1700)

28. Maid cannot describe the target polarization in the D 13 -S 11 region below 800 MeV, but other models fail as well Target Polarization  Maid 2001 data: Bonn 1998

29. However, a fit is possible if a phase difference of ~90° is introduced between the D13(1520) and S11(1535) resonances. But this is impossible within an isobar model. (L. Tiator et al., Phys. Rev. C60 (1999) 035210) Target Polarization  Maid 2001 data: Bonn 1998 model-independent fit

30. Comparison with preliminary data from CB-ELSA total c.s. on proton and neutron (I. Jaegle, priv. comm. 2006)  Maid with a strong D 15 resonance

31. ETA - MAID 2003 standard isobar model (strong D 15,   = 17 % ) reggeized isobar model (weak D 15,   = 0.7 % ) (preliminary data from CB-ELSA, I. Jaegle, priv. comm. 2006) only the model with the strong D 15 can describe the neutron data

34. pentaquark solution

35. open questions for  ‘ missing or misidentified resonances we find S 11 (1904) and P 13 (1926) role of the D 13 resonance are there 2 resonances: D 13 (2080) as given in PDG and a D 13 (1940) as „seen“ in 

36. fit to preliminary  ‘ data from JLab/CLAS (M. Dugger, N*2005 and private comm.) fit to SAPHIR 1998 data

37. open questions for    how many resonances should be built in ? do we really see “missing resonances” ? data discrepancies between SAPHIR and CLAS are very disturbing partial wave analysis in terms of multipoles is not yet possible due to imcomplete database

38. p    total cross section in the second peak the D 13 plays an important role

39. which resonance is important? Resonances found in SAPHIR data analysis Resonances found in CLAS data analysis D 13 (2080)  2 =(  2 all  2 all  N* )/  2 all

40. extracted multipoles Fit 1 Fit 2 Fit 3 Kaon-Maid

41. Summary  nail down the Roper resonance in   improve  database for D waves  solve puzzle of target asymmetry in   it will help to resolve the structure of the S 11 (1535)  clarify the situation with the P 11 pentaquark in   good chance to find missing resonances in  ‘ S 11 (1905), P 13 (1925)   K  may be the most difficult reaction to analyze (large background and many resonances) but probably also the first reaction for a complete experiment

48. comparison of old  ‘-Maid with SAPHIR(98) data only S11 resonance required P11 or even higher resonances are not really necessary