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Results of a search for quasi-bound states of the η meson and a target nucleus obtained during several years using the internal target at the Nuclotron d beam are presented. Formation of η-mesic nuclei was studied in the reaction d + C in the energy interval 1.5Ä2.2 GeV/nucleon Decay products of S11 resonances excited by η mesons captured by nucleons in the nuclear target have been analyzed. Measurements were performed with a scintillation spectrometer SCAN. Analysis of obtained data is presented.

We present the results of a search for and study of the resonance effects in the system of π + π -from the reaction np → npπ + π -at the momentum of quasi monochromatic neutrons P n = (5.20 ± 0.12) GeV/c from the data obtained in an exposure of the 1 m hydrogen bubble chamber of Veksler and Baldin Laboratory of High Energies, Joint Institute for Nuclear Research (VBLHE JINR). After the supplementary selection of the events where a secondary proton was emitted in the forward hemisphere in the general c.m.s. of the reac tion ( > 0) in the effective mass spectrum of π + π -combinations, we found nine peculiarities at the masses ± 11) MeV/c 2 with experimental widths of no more than several tens of MeV/c 2 . We carried out a direct measurement of the spins of resonances and also obtained other quantum numbers. All of these peculiarities have a similar set of quantum numbers I G (J PC ) = 0 + (0 ++ ). We investigated a sequence of scalar isoscalar resonances f 0 (σ 0 ) with masses in the range M ≤ 1200 MeV/c 2 . We found a phenomenological dependence of the resonance mass on its number. This dependence covered not only the resonances shown in this paper, but also those present in PDG tables with quantum numbers of f 0 (σ 0 ) mesons.

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The reaction np → npπ + π − was studied at the various momenta of incident neutrons. It was shown that the characteristics of the reaction at the momenta above 3 GeV/c could be described by the model of reggeized π exchange (OPER). At the momenta below 3 GeV/c, it was necessary to use additionally the mechanism of one baryon exchange (OBE).