Abstract
Since many years the strong final state interaction between η -mesons and light nuclei and the discussed possibility for the formation of η -mesic nuclei has attracted broad experimental and theoretical investigations. Prominent examples are production experiments on the 3 He-η final state which present an unexpected strong total cross section enhancement at threshold, indicating the presence of a pole very close to threshold. Stimulated by these results new proton-deuteron collision experiments on the η meson production have been performed in the near-threshold region and at higher excess energies using both polarized and unpolarized beams. Recent results are presented and discussed in this contribution.
Highlights
Studies on the pd → 3He η or d p → 3He η reaction are motivated by the very anomalous results near threshold [1,2,3,4] as well as by the poorly understood production mechanism
It was suggested that the rapid jump of the total cross section as function of the excess energy Q is an effect of a surprisingly strong final state interaction (FSI) in the η 3He system that might lead to a quasi-bound η-nuclear state [5]
In order to further investigate this system new data with polarized deuteron beams have been taken close to the production threshold at the ANKE spectrometer [7] located at the COSY accelerator of the Forschungszentrum Jülich
Summary
Studies on the pd → 3He η or d p → 3He η reaction are motivated by the very anomalous results near threshold [1,2,3,4] as well as by the poorly understood production mechanism. In order to further investigate this system new data with polarized deuteron beams have been taken close to the production threshold at the ANKE spectrometer [7] located at the COSY accelerator of the Forschungszentrum Jülich. Data at higher excess energies have been taken using the WASA-at-COSY installation which allow for more detailed investigations on the total and differential cross sections which are of high interest for the study of the dominant production processes [9].
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