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