Study of Weak Hyperon Nucleon Interaction by means of Decay Particle Spectroscopy

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It is well known that hadrons (Baryons and mesons) are made up of quarks and gluons by the strong interaction. The interaction among hadrons is not well understood especially due to our inability to describe the quark confinement beased on a known principle. The nucleon nucleon interaction is well described by meson exchange theory except at short distances where size of hadrons has to be taken into account in the model. Quark and gluon degrees of freedom have to be present though flexibility of the meson change model forbits to pin down clearly the existence of the freedom. The SU(3) extention of the model should be the best testing gound for many models that describe well the NN interaction. In the present research we focused our attention to the phenomena which originate short range interaction. Following subjects were studied in this research.(1) Parity violation in the weak nonmesonic decay of hypernuclei.Weak nonmesonic decay NΛ → NN has a large momentum transfer that make interaction at short distance vital. We demonstrated production of polarized Λ hypernuclei and weak nonmesonic decay has asymmetric angular distribution corresponding parity violation. The magnitude of the parity violation is found to be inconsistent with meson exchange model.(2) Spin-orbit interaction of ィイD313(/)ΛィエD3C was measured.Spin-orbit splitting of Λ hypernuclei is known to be small though no definite value has been given by experiments. We produced ィイD313(/)ΛィエD3C by the (KィイD1-ィエD1, πィイD1-ィエD1) using kaon beam provided by the AGS at BNL and measured the splitting by detecting γ rays. The splitting was found to be 20-40 times smaller than that of nucleons.(3) Production of strangeness by weak interaction.We are preparing an experiment to measure the inverse reaction (pn → pΛ) of the weak nonmesonic decay. It is a process to produce strangeness by weak interaction. It has never been challenged. We found that the experiment is feasible by carefully designing the detector.