Study of Low Energy Hyperon-nuclear Reaction with Hybrid Detector

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The purpose of this research project is to study low-energy hyperon nucleus reaction with an emulsion-counter hybrid method. The experiment was carried out at KEK to search for nuclei with S=-2 and the H-dibaryon. The (K^-, K^+) reaction from emul13EA\ : sion nuclei and the XI^- hyperon capture by nuclei following the stopped HI^- in the emulsion were studied in detail. The statistics of the (K^-, K^+) reaction and stopped HI^- have been improved by a factor of hundred over those of old emulsio13EA\ : n experiments.The main results are summarized as follows. 1) The weak decay of nuclei with S=-2 has been confirmed by the following observations ; a) Several hyperfraqments from HI^- capture show sequential weak decay topology which is characteristic of double h13EA\ : hpernuclei. b) The distribution of total visible energy-release and the rate of emission of more than two fast protons, after HI^- capture by heavy nuclei in the emulsion, indicate the sequential weak decay of nuclei with S=-2.2) The observation o13EA\ : f nuclei with S=-2 places a strong limitation on the possible H mass. Especially, one of the events limits the H mass to be larger than 2203.7 +- 0.7 MeV/c^2.3) Through the observation of two single hypernuclei after HI^- capture at rest, two (HI13EA\ : ^--^<12>C) systems, atom or nucleus, are clearly identified for the first time. 4) We searched for the H-dibaryon both in the K^+ momentum spectrum and in the emulsion near the HI^- stopping points, and obtained upper limits for the production of the H.5) The systematics of the (K^-, K^+) reaction and HI^- hyperon capture by nuclei were studied for the first time.