| アブストラクト: |
The LEPS collaboration has performed a search for an $S = +1$ baryon resonance in the $K^-$ missing mass spectrum of the $\gamma n \rightarrow K^+ K^- n$ reaction on $^{12}$C, using a newly built photon-beam facility at the SPring-8, motivated in part by the recent work by Diakonov, Petrov and Polyakov who studied anti-decuplet
baryons using the chiral soliton model. A sharp baryon resonance peak
has been found at $1.54 \pm 0.01$ GeV/$c^2$ in the $K^-$ missing mass
spectrum that is corrected for the Fermi motion. The Gaussian significance of the peak is 4.6 $\sigma$ and the width is estimated to be smaller than 25 MeV/$c^2$. This strongly indicates the existence of a narrow $S = +1$ resonance which may be attributed to the molecular
meson-baryon resonance or alternatively as an exotic 5-quark state ($uudd\bar{s}$) that decays into a $K^+$ and a neutron. The mass and width of the resonace is consistent with the $\Theta^+$, the lowest member of the anti-decuplet, predicted by the chiral soliton model.
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