Nuclear mass form factors from coherent photoproduction of π0\pi^0 mesons

Data for coherent photoproduction of $\pi^0$ mesons from nuclei ($^{12}$C, $^{40}$Ca, $^{93}$Nb, $^{nat}$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 $A(\gamma ,\pi^0)A$ 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 $q^2\to 0$. 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.

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 $\pi^o X$, $\eta X$, $2\pi^oX$ and $\pi^o\pi^{\pm}X$) from the nuclei $^{12}$C, $^{40}$Ca, $^{93}$Nb, and $^{208}$Pb up to the second resonance region. The results were analyzed in view of the in-medium properties of the P$_{33}$(1232), the D$_{13}$(1520), and the S$_{11}$(1535) resonances.Comment: to be published in Acta Physica Hungaric

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

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

Photoproduction of Mesons off Light Nuclei -- the Search for \eta -Mesic Nuclei

Photoproduction of \eta mesons off light nuclei (d, 3He, 7Li) has been measured at the tagged photon beam of the Mainz MAMI accelerator with the combined Crystal Ball/TAPS detection system. Special attention was given to the threshold behavior of the reactions in view of possible indications for the formation of (quasi-) bound \eta -nucleus states, so-called \eta -mesic nuclei. A very strong threshold enhancement of coherent \eta photoproduction off 3He was found and coherent \eta photoproduction off 7Li was observed for the first time. Preliminary results will be discussed.Comment: Invited talk at the International Symposium on Mesic Nuclei, Krakow, 16 June 201

Experimental Review of Baryons in the Nuclear Medium

Inclusive studies of nuclear photoabsorption have provided clear evidence of medium modifications but the results have not yet been explained in a model independent way. A deeper understanding of the situation is anticipated from a detailed experimental study of meson photoproduction from nuclei in exclusive reactions. Recent results on meson production in photonuclear experiments indicate a large difference between quasifree meson production from the nuclear surface and non-quasifree components.Comment: Proceedings Baryons200

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