1,973 research outputs found
Nuclear mass form factors from coherent photoproduction of mesons
Data for coherent photoproduction of mesons from nuclei (C,
Ca, Nb, Pb), recently measured with the TAPS detector at
the Mainz MAMI accelerator, have been analyzed in view of the mass form factors
of the nuclei. The form factors have been extracted in plane wave approximation
of the reaction and corrected for final state interaction
effects with the help of distorted wave impulse approximations. Nuclear mass
rms-radii have been calculated from the slope of the form factors for . Furthermore, the Helm model (hard sphere form factor folded with Gaussian)
was used to extract diffraction radii from the zeroes of the form factor and
skin thicknesses from the position and height of its first maximum. The
diffraction radii from the Helm model agree with the corresponding charge radii
obtained from electron scattering experiments within their uncertainties of a
few per cent. The rms-radii from the slope of the form factors are
systematically lower by up to 5% for PWIA and up to 10% for DWIA. Also the skin
thicknesses extracted from the Helm model are systematically smaller than their
charge counter parts.Comment: Accepted for publication in Eur. Phys. J.
Photoproduction of eta-mesons from light nuclei
In a series of experiments coherent and quasifree eta-photoproduction from
light nuclei (4He, 3He, 2H) was investigated with the TAPS-detector at the
Mainz MAMI-accelerator. The experiments were motivated by two different
subjects: the determination of the isospin structure of the electromagnetic
excitation of the S11(1535) resonance and the study of the eta-nucleon and
eta-nucleus interaction at small momenta. The results for the deuteron and 4He
are summarized and first preliminary results for 3He are presented.Comment: 5 pages, 3 figures, Proceedings of Meson2002 workshop, Kraka
In-medium properties of nucleon resonances
Recent experimental results for the in-medium properties of nucleon
resonances are discussed. The experiments were done with the TAPS detector at
the tagged photon beam of the MAMI accelerator in Mainz. Measured was the
photoproduction of mesons (final states , , and
) from the nuclei C, Ca, Nb, and
Pb up to the second resonance region. The results were analyzed in view
of the in-medium properties of the P(1232), the D(1520), and the
S(1535) resonances.Comment: to be published in Acta Physica Hungaric
Surface and volume effects in the photoabsorption of nuclei
Recent experimental results for meson photoproduction from nuclei obtained
with TAPS at MAMI are analyzed in view of the suppression of the second nucleon
resonance region in total photoabsorption. The cross sections can be split into
a component from the low density surface region of nuclei and a component which
scales more like the nuclear volume. The energy dependence of the surface
component is similar to the deuteron cross section, it shows a clear signal for
the second resonance peak assigned to the excitation of the P11(1440),
D13(1520), and S11(1535). The volume component behaves differently, it is
lacking the second resonance peak and shows an enhancement at intermediate
photon energies.Comment: accepted for publication in Eur. J. Phys.
Study of Non-Strange Baryon Resonances with Meson Photoproduction
Photoproduction of mesons is an excellent tool for the study of nucleon
resonances. Complementary to pion induced reactions, photoproduction on the
free proton contributes to the determination of the basic properties of nucleon
resonances like excitation energy, decay widths, spin, and the coupling to the
photon. Photoproduction from light nuclei, in particular from the deuteron,
reveals the isospin structure of the electromagnetic excitation of the nucleon.
During the last few years, progress in this field has been substantial. New
accelerator facilities combined with state-of-the-art detector technologies
have pushed the experiments to unprecedented sensitivity and precision. The
experimental progress has been accompanied by new developments for the reaction
models, necessary to extract the properties of the nucleon states, and for
modern hadron models which try to connect these properties to QCD. The emphasis
of this review lies on the experimental side and focuses on experiments aiming
at precise studies of the low-lying nucleon resonances.Comment: 87 pages, 67 figures, Prog. Part. Nucl. Phys., accepte
Hadrons in Nuclei: Experiments and Perspectives
The question of the origin of hadron masses is one major issue in the
understanding of the strong interaction. The challenge is addressed by
searching for indications of in-medium modifications of hadron properties and
studying hadrons in nuclei. The quest driving in-medium studies is to
understand the origin of hadron masses in the context of spontaneous chiral
symmetry breaking.
The experimental status of the modification of hadron properties in the
nuclear medium is discussed including experiments using hadron, heavy-ion, and
photon beams. Particular emphasis is put on the production of light mesons from
nuclei.
A number of experimental programs is underway to provide a detailed
comparison of properties of free hadrons and hadrons embedded in nuclei. The
existing experimental efforts are discussed and possibilities are introduced
for the new WASA-at-COSY facility, initially focussed on investigations of
symmetries and symmetry breaking, to contribute to the field.Comment: To appear in the proceedings of 23rd International Nuclear Physics
Conference (INPC 2007), Tokyo, Japan, 3-8 Jun 200
Extraction of the Ratio of the N^*(1535) Electromagnetic Helicity Amplitudes from Eta Photoproduction off Neutrons and Protons
Using the recent precise measurements of eta photopro- duction in proton and
deuteron targets, we extract the ratio of the helicity amplitudes A^n_1/2 /
A^p_1/2, for the excitation of N^*(1535), in the effective Lagrangian approach,
It is fairly model-independent, free from the final-state interaction effects,
and negative as predicted by the quark models. We stress the importance of
polarization observables in further elucidation of the N^*(1520)
photoexcitation amplitudes.Comment: 4 figures. It will be published in Phys. Lett.
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