3,570 research outputs found
Models of Meson-Baryon Reactions in the Nucleon Resonance Region
It is shown that most of the models for analyzing meson-baryon reactions in
the nucleon resonance region can be derived from a Hamiltonian formulation of
the problem. An extension of the coupled-channel approach to include
channel is briefly described and some preliminary results for the
excitation are presented.Comment: Latex 13 pages; to appear in the Proceedings of Workshop on the
Physics of excited nucleons (NSTAR2004), Grenoble (France), March 24-27, 200
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
Strain differences in carcinogenesis by urethane administration to suckling mice with special reference to induction of lung cancer.
Disentangling the dynamical origin of P11 Nucleon Resonances
We show that two almost degenerate poles near the threshold and
the next higher mass pole in the partial wave of scattering
evolve from a single bare state through its coupling with , and
reaction channels. This finding provides new information on
understanding the dynamical origins of the Roper and
resonances listed by Particle Data Group. Our results for the resonance poles
in other partial waves are also presented.Comment: Improved version, accepted Phys. Rev. Let
Dynamical Coupled-Channels Effects on Pion Photoproduction
The electromagnetic pion production reactions are investigated within the
dynamical coupled-channels model developed in {\bf Physics Reports, 439, 193
(2007)}. The meson-baryon channels included in this study are , , , and the , and resonant components
of the channel. With the hadronic parameters of the model determined
in a recent study of scattering, we show that the pion photoproduction
data up to the second resonance region can be described to a very large extent
by only adjusting the bare helicity amplitudes, while the
non-resonant electromagnetic couplings are taken from previous works. It is
found that the coupled-channels effects can contribute about 10 - 20 % of the
production cross sections in the (1232) resonance region, and can
drastically change the magnitude and shape of the cross sections in the second
resonance region. The importance of the off-shell effects in a dynamical
approach is also demonstrated. The meson cloud effects as well as the
coupled-channels contributions to the form factors are found
to be mainly in the low region. For the magnetic M1
(1232) form factor, the results are close to that of the Sato-Lee Model.
Necessary improvements to the model and future developments are discussed.Comment: Corrected version. 14 pages, 10 figure
Dynamical coupled-channels analysis of 1H(e,e'pi)N reactions
We have performed a dynamical coupled-channels analysis of available
p(e,e'pi)N data in the region of W < 1.6 GeV and Q^2 < 1.45 (GeV/c)^2. The
channels included are gamma^* N, pi N, eta N, and pi pi N which has pi Delta,
rho N, and sigma N components. With the hadronic parameters of the model
determined in our previous investigations of pi N --> pi N, pi pi N reactions,
we have found that the available data in the considered W < 1.6 GeV region can
be fitted well by only adjusting the bare gamma^* N --> N^* helicity amplitudes
for the lowest N^* states in P33, P11, S11 and D13 partial waves. The
sensitivity of the resulting parameters to the amount of data included in the
analysis is investigated. The importance of coupled-channels effect on the
p(e,e' pi)N cross sections is demonstrated. The meson cloud effects, as
required by the unitarity conditions, on the gamma^* N --> N^* form factors are
also examined. Necessary future developments, both experimentally and
theoretically, are discussed.Comment: 14 pages, 11 figures. Version to appear in PR
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