5-quark baryon \Theta⁺ with S=+1 was discovered in photoproduction from the neutron in ¹²C at LEPS of SPring-8. A Gaussian significance was 4.6\sigma . The mass and width of the \Theta⁺ were 1.54\pm 0.01 GeV/c² and smaller than 25 MeV/c², respectively. Recent results from other experiments confirmed the existence of the \Theta⁺. The \Theta⁺ can be interpreted as a molecular meson--baryon resonance or alternatively as an exotic five quark state (uudd\bar {s}). Photon beam asymmetries for the p(\gamma , K⁺)\Lambda and p(\gamma , K⁺){\Sigma }⁰ reactions were measured at E_\gamma =1.5--2.4 GeV and 0.6< cos (\theta ^c.m._K⁺)<1.0 by using linearly polarized photon beam. The measured asymmetries are positive and gradually increase with rising photon energy. There is no theoretical prediction which perfectly reproduces the measurements. Including the new results in the development of theoretical models is crucial for understanding the reaction mechanism and to test the presence of missing resonances.

PACS numbers: 13.60.Le, 13.60.Rj, 14.20.Jn