Study of Hyperon-Nucleon Interaction

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We have made several discoveries in hypernuclear physics. During the analysis of the nuclear emulsion obtained by KEK-E373 experiment, we found several double hypernuclei. One is ^6He_ΛΛ nucleus and its mass was precisely determined. From the binding energy of the two Λ of this nucleus, ΛΛ interaction was determined to be weakly attractive for the first time. The result is quite important to construct models of baryon-baryon was interaction. The high precision γray spectroscopy of hypernuclei has provided very rich physics results. Recent measurements with Hyperball for ^7Li,^9Be and ^<16>O hypernuclei have almost determined ΛN spin-dependent interaction, such as spin-spin, spin-orbit and tensor interaction. Especially, spin-orbit interaction determimed by a level splitting of 40kev of spin doublet states of ^9Be hypernucleus was found very weak compared to the nucleon-nucleon case by almost two orders of magnitude.At KEK-PS, we have performed an experiment (E522) with a 1.66GeV/c K- b … More eam to study a possible H-dibaryon resonance and ΞN interaction. We took a largest data for (K-,K+) reactions with a scintillating fiber active target. We have analyzed counter data and visual data obtained by the scintillating fiber. About 40k (K-,K+) reactions were scanned with computer-aided scanning system. Among them we have obtained about 200 events which show emission of two Λ from the (K-K+) reaction vertices. The invariant mass spectrum of the two Λ shows a peak near the threshold which may suggest the existence of H-dibaryon resonance.We have constructed a Time Projection Chamber (TPC) for the study of hyperon resonances with Laser Compton γ beam at Spring-8. The characteristics of the TPC is that a target is located inside the TPC. This makes it possible to detect decays of low energy hyperons which has only a few cm flight length. The primary goal is to measure Λ(1405) with nuclear targets to clarify its structure. We have studied the properties of the TPC with cosmic rays. We have obtained the position resolution of 300μm and 500μm in Θ and z directions, respectively. In the end of 2003, we installed the TPC in a superconducting solenoid and started data taking together with a forward spectrometer with the γbeam. The TPC has been successfully operated at the beam rate of 10^6 Hz. Preliminary analysis shows that charged particle tracks are clearly recorded by the TPC. Less