nstars: open questions
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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
- 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
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
current situation with the Pcurrent situation with the P1111 (Roper) multipoles (Roper) multipoles
W=1440 MeVW=1710 MeV
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
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
which resonance is important?
Resonances found in SAPHIR data analysis
Resonances found in CLAS data analysis
D13 (2080)
2=(2all2
allN*)/2all
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
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