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[en] An η factory has been installed at Saclay. The η are produced by the pd→3Heη reaction near threshold and tagged by the detection of 3He in a magnetic spectrometer. The rate of tagged η is 105/s. Rare decays of the η meson will be investigated, beginning with η→μ+μ- where the μ will be detected in range telescopes. Magnetic spectrometers for lepton detection are considered for future experiments
[en] The decays of non-strange positive parity baryons via emission of a pseudo-scalar meson are studied in the framework of the 1/Nc expansion to order 1/Nc. In particular, the pionic decays of the l=0 Roper baryons and of the l=2 baryons in the mass interval 1680-1950 MeV are analyzed using the available partial decay widths. Decay widths by emission of an eta meson are shown to be suppressed by a factor 1/Nc2 with respect to the pionic ones
[en] A three-body force acting between the η-meson and two nucleons was overlooked inadvertently in the model description and discussion in the published version of our paper “Onset of η-nuclear binding in a pionless EFT approach” [Phys. Lett. B 771 (2017) 297–302] while present in the actual numerical calculations. The stated conclusion that a stabilizing ηNN contact term was not needed is therefore incorrect. Such a three-body force, associated with a new low energy constant , must be introduced at leading order to stabilize η-nucleus systems.
[en] The isobarmodel, which reproduced fairly well experimental data on η′-meson photoproduction at photon energies between 1500 and 3700 MeV, is refined with allowance for new experimental data in the vicinity of the reaction threshold.
[en] Eta-mesic nucleus or the quasibound nuclear state of an eta (η) meson in a nucleus is caused by strong interaction force alone. This new type of nuclear species, which extends the landscape of nuclear physics, has been extensively studied since its prediction in 1986. We review and analyze in great detail the models of the fundamental η-nucleon interaction leading to the formation of an η-mesic nucleus, the methods used in calculating the properties of a bound η, and the approaches employed in the interpretation of the pertinent experimental data. In view of the successful observation of the η-mesic nucleus "2"5Mg_η and other promising experimental results, future direction in searching for more η-mesic nuclei is suggested
[en] Model-independent estimates obtained for the Breit-Wigner parameters of the S11(1535) and S11(1650) nucleon resonances from the latest experimental data on the photoproduction of eta mesons on protons are reported.
[en] The authors report on a novel design for a compact magnetic spectrometer to study η physics. The design uses two 40 cm diameter superconducting solenoids separated by a gap of 45 cm which allows approximately 3π acceptance for two body processes. Properties of the field and design criteria for the major components of the detector are discussed