13,739 research outputs found
Dynamical coupled-channels: the key to understanding resonances
Recent developments on a dynamical coupled-channels model of hadronic and
electromagnetic production of nucleon resonances are summarized.Comment: Invited Plenary talk at the 20th European Conference on Few-Body
Problems in Physics (EFB20), September 10-14 2007, Pisa, Italy. To appear in
the proceedings in Few-Body System
Extraction of P11 Resonance from pi-N Data and Its Stability
An important question about resonance extraction is how much resonance poles
and residues extracted from data depend on a model used for the extraction, and
on the precision of data. We address this question with the dynamical
coupled-channel (DCC) model developed in Excited Baryon Analysis Center (EBAC)
at JLab. We focus on the P11 pi-N scattering. We examine the model-dependence
of the poles by varying parameters to a large extent within the EBAC-DCC model.
We find that two poles associated with the Roper resonance are fairly stable
against the variation. We also develop a model with a bare nucleon, thereby
examining the stability of the Roper poles against different analytic structure
of the P11 amplitude below pi-N threshold. We again find a good stability of
the Roper poles.Comment: 6 pages, 8 figures, Contribution to the proceedings of 24th
International Nuclear Physics Conference (INPC), Vancouver, Canada, 4-9 July
201
Double and single pion photoproduction within a dynamical coupled-channels model
Within a dynamical coupled-channels model which has already been fixed from
analyzing the data of the pi N -> pi N and gamma N -> pi N reactions, we
present the predicted double pion photoproduction cross sections up to the
second resonance region, W< 1.7 GeV. The roles played by the different
mechanisms within our model in determining both the single and double pion
photoproduction reactions are analyzed, focusing on the effects due to the
direct gamma N -> pi pi N mechanism, the interplay between the resonant and
non-resonant amplitudes, and the coupled-channels effects. The model parameters
which can be determined most effectively in the combined studies of both the
single and double pion photoproduction data are identified for future studies.Comment: Version to appear in PRC. 16 pages, 13 figure
Derivation of a multilayer approach to model suspended sediment transport: application to hyperpycnal and hypopycnal plumes
We propose a multi-layer approach to simulate hyperpycnal and hypopycnal
plumes in flows with free surface. The model allows to compute the vertical
profile of the horizontal and the vertical components of the velocity of the
fluid flow. The model can describe as well the vertical profile of the sediment
concentration and the velocity components of each one of the sediment species
that form the turbidity current. To do so, it takes into account the settling
velocity of the particles and their interaction with the fluid. This allows to
better describe the phenomena than a single layer approach. It is in better
agreement with the physics of the problem and gives promising results. The
numerical simulation is carried out by rewriting the multi-layer approach in a
compact formulation, which corresponds to a system with non-conservative
products, and using path-conservative numerical scheme. Numerical results are
presented in order to show the potential of the model
Extraction of P11 resonances from pi N data
We show that two P11 nucleon resonance poles near the pi Delta threshold,
obtained in several analyses, are stable against large variations of parameters
within a dynamical coupled-channels analysis based on meson-exchange
mechanisms. By also performing an analysis based on a model with a bare nucleon
state, we find that this two-pole structure is insensitive to the analytic
structure of the amplitude in the region below pi N threshold. Our results are
M_pole = (1363^{+9}_{-6} -i79^{+3}_{-5}) MeV and (1373^{+12}_{-10}
-i114^{+14}_{-9}) MeV. We also demonstrate that the number of poles in the 1.5
GeV < W < 2 GeV region could be more than one, depending on how the structure
of the single-energy solution of SAID is fitted. For three-pole solutions, our
best estimated result of a pole near N(1710) listed by Particle Data Group is
(1829^{+131}_{-65} -i192^{+88}_{-110}) MeV which is close to the results of
several previous analyses. Our results indicate the need of more accurate pi N
reaction data in the W > 1.6 GeV region for high precision resonance
extractions.Comment: 15 pages, 4 figure
Single photo and electroproduction of pions at EBAC@JLAB
Within the Excited Baryon Analysis Center we have performed a dynamical
coupled-channels analysis of the available data in the region of
1.6 GeV and 1.45 (GeV/c). The channels included are
, , , and which has , , and components. With the hadronic parameters of the model
determined in our previous investigations of reaction, we have
found that the available data in the considered 1.6 GeV region can be
fitted well by only adjusting the bare helicity amplitudes
for the lowest states in , , and
partial waves. The meson cloud effect, as required by the unitarity conditions,
on the form factors are examined.Comment: 6 pages, invited talk at NSTAR 2009, Beijing (China), 2009, to appear
in the proceeding
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