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Nucleon Resonances in Nucleon Resonances in Scattering Scatteringup to energies up to energies W < 2.0 GeVW < 2.0 GeV
introduction
a meson-exchange model for scattering
conventional resonance parameters
pole positions and residues
summary and outlook
G.Y. Chen, S.S. Kamalov, S.N. Yang, D. Drechsel and L.T.NTU Taipei, JINR Dubna, Universität Mainz
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• dynamical meson exchange models for pion-nucleon scattering have been developed over many years, mostly in the energy region of the resonance
• the first goal is to extract N* parameters to investigate the structure of QCD and to compare with lattice calculations
• an open question is still: How can we understand the very successfull description of N* properties by constituent quark models
• and why does it fail in some other cases
Dynamical ModelsDynamical Models
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• another important point is the dynamical amplitude(formerly called off-shell amplitude), which plays a significant role in electromagnetic reactions,
like loop effects in pion photoproduction
• within the dynamical models one can calculate the pion-loop contributions for threshold photo- and electroproduction in a similar way as in ChPT,
but unrestricted in energy and momentum
Dynamical ModelsDynamical Models
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previous work on Taipei meson exchange previous work on Taipei meson exchange model:model:
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recent work on dynamical models for W<2 recent work on dynamical models for W<2 GeV:GeV:
Mainz-Dubna-Taipei:Mainz-Dubna-Taipei:
Chen, Kamalov, Yang, Drechsel, L.T., nucl-th/0703096
with nucleon resonance analysis (this presentation)
EBAC (JLab):EBAC (JLab):
Diaz, Lee, Matsuyama, Sato, nucl-th/0704.1615
with first step of a bigger project
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results of the fits to the SAID partial wavesresults of the fits to the SAID partial waves
S wavesS waves
single-energy pw analysis from SAID
nonresonant background
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P wavesP waves
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D and F wavesD and F waves
we find noimprovementincluding F17(1990)
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Extraction of resonance Extraction of resonance parametersparameters
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bare and physical resonance masses, total widths, bare and physical resonance masses, total widths, branching ratios and background phases branching ratios and background phases
for N* resonances (I=1/2)for N* resonances (I=1/2)
bare phys
our analysisPDG
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our analysisPDG
baremass
physical mass
additional res.
additional res.
additional res.
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resonance parametersresonance parametersfor for resonances (I=3/2) resonances (I=3/2)
baremass
physical mass
our analysisPDG
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resonance parametersresonance parametersfor for resonances (I=3/2) resonances (I=3/2)
baremass
physical mass
our analysisPDG
additional res.
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pole positions and residuespole positions and residuesfor N* resonances (I=1/2)for N* resonances (I=1/2)
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pole positions and residuespole positions and residuesfor N* resonances (I=1/2)for N* resonances (I=1/2)
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pole positions and residuespole positions and residuesfor for resonances (I=3/2)resonances (I=3/2)
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pole positions and residuespole positions and residuesfor for resonances (I=3/2)resonances (I=3/2)
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a new meson-exchange model has been presented for pion nucleon scattering that fits the S,P,D,F waves very well up to W = 2.3 GeV
for all but one PDG resonances below 2200 we can determine conventional resonance parameters and pole positions
we cannot find the F17(1990) resonance (same as SAID),but find 4 broad states that are not listed in PDG: S11(1878), D13(2152), P13(2204), P13(2204)
this model is very well suited for an application ofpion and eta photo- and electroproduction
Summary and Summary and ConclusionsConclusions