Nstars: Open Nstars: Open Questions Questions

L. Tiator, Institut für Kernphysik, Universität Mainz

Introduction

Roper and S11

the role of the D15 or P11 pentaquark in eta production

missing resonances in etaprime and kaon production

Summary and Conclusion

MAID collaborationMAID collaboration

Dieter Drechsel and L.T.Institut für Kernphysik, Universität Mainz, Germany

Sabit KamalovLaboratory 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

What is a resonance? What is a resonance?

- a peak in the cross section

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

P33 partial wave

W=1232 MeV

S11 partial wave

W=1535 MeV

no zero crossing for S11(1535)it works for the (1232)

pw amplitudes of pion photoproductionpw amplitudes of pion photoproduction

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

Argand Diagrams and Speed-PlotsArgand Diagrams and Speed-Plots

What is the origin of a resonance? What is the origin of a resonance?

- a (qqq) bound or excited state with possibleadmixtures of (qqqg) or (qqq qq) etc.

- a dynamically generated object of nucleon + meson interaction, e.g.:

(1232) = N + does not workP11(1440) = N + may work well (e.g. Krewald et al)

(but e.m. properties are not yet tested)

S11(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)

How can resonances be tested?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

4 missing resonances in the gap4 missing resonances in the gap

1800 MeV < W < 1900 MeV1800 MeV < W < 1900 MeV

open questions foropen questions for

• Roper and S11 resonances

• photon couplings of most resonances are still quite

inaccurate, even for 4-star

• D13 partial wave has ambigous solutions below the

resonance

comparison between MAID and SAIDcomparison between MAID and SAID

comparison between MAID and SAIDcomparison between MAID and SAID

SAIDMAID

comparison between MAID and SAIDcomparison between MAID and SAID

current situation with the Pcurrent situation with the P1111 (Roper) multipoles (Roper) multipoles

W=1440 MeVW=1710 MeV

CB proposal with MAMI CCB proposal with MAMI C

open questions for open questions for

• qqq resonances vs. dynamically generated resonances

with N or with , e.g. S11(1535)

• target asymmetry in S11/D13 region

• exotic resonances: Does the + pentaquark exist?

if so, it should have a non-strange partner

P11(~1700)

Maid cannot describe the target polarization in the D13-S11 region

below 800 MeV, but other models fail as well

Target PolarizationTarget Polarization

Maid 2001

data: Bonn 1998

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 PolarizationTarget Polarization

Maid 2001

data: Bonn 1998

model-independentfit

Comparison with preliminary data from CB-ELSAComparison with preliminary data from CB-ELSAtotal c.s. on proton and neutron (I. Jaegle, priv. comm. 2006)

Maid with a strong D15 resonance

ETA - MAID 2003ETA - MAID 2003

standard isobar model

(strong D15, = 17 %)

reggeized isobar model

(weak D15, = 0.7 %)

(preliminary data from CB-ELSA, I. Jaegle, priv. comm. 2006)

only the model with the strong D15 can describe the neutron data

pentaquark solution

open questions for open questions for ‘‘

• missing or misidentified resonances

• we find S11(1904) and P13(1926)

• role of the D13 resonance

are there 2 resonances: D13(2080) as given in PDG

and a D13(1940) as „seen“ in

fit to preliminary fit to preliminary ‘ data from ‘ data from JLab/CLASJLab/CLAS(M. Dugger, N*2005 and private comm.)

fit to SAPHIR 1998 data fit to SAPHIR 1998 data

open questions for 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

pptotal cross sectiontotal cross section

in the second peak

the D13 plays an important role

which resonance is important?

Resonances found in SAPHIR data analysis

Resonances found in CLAS data analysis

D13 (2080)

2=(2all2

allN*)/2all

extracted multipolesextracted multipolesFit 1Fit 2Fit 3Kaon-Maid

Summary 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 S11(1535)

clarify the situation with the P11 pentaquark in

good chance to find missing resonances in ‘ S11(1905), P13(1925)

Kmay be the most difficult reaction to analyze (large background and many resonances) but probably also the first reaction for a complete experiment

comparison of old comparison of old ‘-Maid with SAPHIR(98) data ‘-Maid with SAPHIR(98) data

only S11 resonance requiredP11 or even higher resonancesare not really necessary