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
• 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
• 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
previous work on Taipei meson exchange previous work on Taipei meson exchange model:model:
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
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
P wavesP waves
D and F wavesD and F waves
we find noimprovementincluding F17(1990)
Extraction of resonance Extraction of resonance parametersparameters
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
our analysisPDG
baremass
physical mass
additional res.
additional res.
additional res.
resonance parametersresonance parametersfor for resonances (I=3/2) resonances (I=3/2)
baremass
physical mass
our analysisPDG
resonance parametersresonance parametersfor for resonances (I=3/2) resonances (I=3/2)
baremass
physical mass
our analysisPDG
additional res.
pole positions and residuespole positions and residuesfor N* resonances (I=1/2)for N* resonances (I=1/2)
pole positions and residuespole positions and residuesfor N* resonances (I=1/2)for N* resonances (I=1/2)
pole positions and residuespole positions and residuesfor for resonances (I=3/2)resonances (I=3/2)
pole positions and residuespole positions and residuesfor for resonances (I=3/2)resonances (I=3/2)
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
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