266 research outputs found
Spin structure of the Delta(1232) and inelastic Compton scattering
Radiative transitions gamma + Delta(1232) -> N^* are discussed in the
nonrelativistic quark model with spin-orbit corrections for the 70-plet L^P=1^-
nucleon resonances N^*. The reaction gamma + N -> gamma + Delta is considered
as a tool to measure some of these transitions. A particular sensitivity to
photoexcitations of S_{11}(1535), D_{13}(1700), and D_{15}(1675) is predicted.Comment: 4 pages, 1 figure. Talk given at NSTAR01, Mainz, German
The GDH sum rule for the Delta isobar: A possible anomaly?
The GDH sum rule is discussed for the Delta(1232) resonance. It is shown that
apart from ordinary excitations to higher-energy states, the sum rule contains
a large negative contribution due to de-excitation into the nucleon state.
Therefore, a fulfillment of the sum rule assumes a strong coupling of Delta^+
and Delta^0 to resonances of spin 5/2 and higher. Calculations performed in
quark models suggest that D15(1675) may be such a resonance. However, its
strength is found to be not sufficient for bringing the GDH sum rule to a
theoretically expected positive magnitude.Comment: 5 pages, no figures. Extended talk at the GDH2000 Symposium, Mainz,
June 14-17, 2000. To appear in proceeding
Deuteron Compton scattering and electromagnetic polarizabilities of the nucleon
Differential cross section of deuteron Compton scattering has been calculated
using the Bonn NN-potential, a consistent set of meson-exchange currents and
seagulls, and lowest- and higher-order electromagnetic polarizabilities of the
nucleon. Estimates of the polarizabilities of the neutron are obtained from
recent experimental data.Comment: 3 pages, 2 figures, Latex2e with ps fonts. Talk at the FB16
Conference, Taipei, March 6-10, 2000. To appear in proceeding
Structure of the -meson and diamagnetism of the nucleon
The structure of the meson and the diamagnetism of the nucleon are
shown to be topics which are closely related to each other. Arguments are found
that the meson couples to two photons via its non-strange
structure component. This ansatz leads to a quantitative explanation of the
-channel component of the difference of electromagnetic polarizabilities,
(\alpha-\beta)^t(\alpha-\beta)^t_{p,n}=(5\alpha_e g_{\pi MM})/(6\pi^2 m^2_\sigma
f_\pi)=15.310^{-4}{\rm fm}^3(\alpha-\beta)^t_p=15.1\pm 1.3(\alpha-\beta)^t_n=14.8\pm 2.7\pi\pi\sigma(\alpha-\beta)^t_{p,n}=14\pm 2$, what also is in agreement with
the experimental results.Comment: Contribution made by Martin Schumacher to the International Workshop
on the Physics of Excited Baryons, 12 - 15 Oct. 2005, Tallahasse, Florida US
Observation of eta-mesic nuclei in photoreactions: results and perspectives
Recent results from the LPI experiment on searching for eta-mesic nuclei in
photoreactions are discussed and further perspectives are summarized.Comment: 4 pages, 4 figures. Talk given by G.A.S. at NSTAR01, Mainz, German
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