Solution of the eta-4He problem with quasi-particle formalism

The Alt-Grassberger-Sandhas equations for the five-body eta-4N problem are solved for the case of the driving eta N and NN potentials limited to s-waves. The quasi-particle (Schmidt) method is employed to convert the equations into the effective two-body form. Numerical results are presented for the eta-4He scattering length.Comment: 8 pages, 5 figure

Three-body analysis of incoherent η\eta-photoproduction on the deuteron in the near threshold region

A three-body calculation of the reaction $\gamma d\to\eta np$ in the energy region from threshold up to 30 MeV above has been performed. The primary goal of this study is to assess the importance of the three-body aspects in the hadronic sector of this reaction. Results are presented for the $\eta$-meson spectrum as well as for the total cross section. The three-body results differ significantly from those predicted by a simple rescattering model in which only first-order $\eta N$- and $NN$-interactions in the final state are considered. The major features of the experimental data are well reproduced although right at threshold the rather large total cross section could not be explained.Comment: 6 pages revtex including 3 figure

Spin asymmetry and GDH sum rule for real and virtual photons for the deuteron

An explicit evaluation of the spin asymmetry of the deuteron and the associated GDH sum rule is presented which includes disintegration, single and double pion and eta production. For the GDH integral a large cancellation is found between the disintegration channel and the meson production channels. Furthermore, first results for the contribution of the disintegration channel to the generalized GDH integral at constant four-momentum transfer reveal a dominance of the isovector M1 transition to the $^1$S$_0$-state near threshold resulting in a negative contribution with a minimum around $Q^2\approx 0.2$ fm$^{-2}$ which is driven by the nucleon anomalous isovector magnetic moment.Comment: 9 pages, 7 figures, World Scientific style, invited talk at GDH 2004 Symposiu

Interaction of η\eta mesons with a three-nucleon system

A study of the $\eta$-3N interaction in the energy region near the $\eta$-^3H elastic scattering threshold is presented. The calculational scheme is based on the four-body scattering formalism. A manageable form of the integral equations is achieved by using a separable ansatz for the driving two-body $\eta N$- and NN-forces as well as for the subamplitudes appearing in the (1+3) and (2+2) partitions of the $\eta$-3N system. Results presented for the $\eta$-^3H scattering length point to the existence of a virtual (antibound) s-wave $\eta$-^3H state. As a consequence, a large enhancement of the cross section for $\eta$-production from three-body nuclei is predicted.Comment: 4 pages including 2 eps-figures, Contribution to MESON 2002, 7th Int. Workshop on Production, Properties and Interaction of Mesons, Cracow, Poland, May 24-28, 200