Data Entry: Please note that the research database will be replaced by UNIverse by the end of October 2023. Please enter your data into the system https://universe-intern.unibas.ch. Thanks
PHOTOPRODUCTION OF eta-MESONS AND eta pi-PAIRS OFF LIGHT NUCLEI
Journal
Acta physica Polonica. B, Elementary particle physics, nuclear physics, theory of relativity, field theory
Volume
45
Number
3
Pages / Article-Number
639-653
Abstract
Photoproduction of eta-mesons has been measured for several light nuclei (H-2, He-3, Li-7) and photoproduction of eta pi-pairs was investigated for a deuteron target. The experiments were done at the tagged photon beam of the Mainz MAMI accelerator with the Crystal Ball/TAPS electromagnetic calorimeter. They aimed at two topics: the extraction of cross section data for the elementary reactions off neutrons and the investigation of the eta-nucleus interactions, in view of eta-mesic states. The main results are: the excitation function for the gamma n -> n eta reaction has a very narrow structure (width around 30 MeV) at final state invariant masses of 1670 MeV. Its nature is not yet understood. For the quasi-free production of eta pi-pairs, the analysis of all isospin channels (final states p eta pi r(0), n eta pi(0), p eta pi(-), and n eta pi(+)) resulted in cross section ratios almost perfectly agreeing in the threshold region with a dominant contribution from the D-33 -> eta P-33(1232) ->eta pi N decay chain. The measurement of coherent eta-production off 3He and 7Li nuclei confirmed a strong threshold enhancement accompanied by almost isotropic angular distributions for the He-3 nucleus and much smaller deviations from PWIA approximations for the 7Li nucleus, supporting the special role of He-3 as a candidate for eta-mesic nucleus formation.
