| Research Abstract |
In two nucleon system the strong repulsion exists in the short-range part of the force. Then,if a resonance or quai-bound state appears, it is anormalous. The study of this state has possibility to guide one to a new concept.
(1)We have analysed the nucleon-nucleon scattering data at E_L=500-800 MeV comprehensively. The eigenstates which cause the two narrow structures in the analysing power A_y are identified. The structure at E_L=610 MeV is due to the ^3F_3 or ^3H_5 state, while the one at E^L=680 MeV is due to the ^1G_4, ^3P_1,^3F_4 or ^3H_5 state. To select uniquely the solution from these plural ones, necessary and effective observables are pointed out.
(2)In Faddeev calculation we have solved etaNN-piNN coupled system with two-body interaction input. We find a quasi-bound state with width 20 MeV at energy 10 MeV below the etaNN threshold. This quasibound state is generated in cooperation of strongly attractive forces existing in both the etaN S_<11> and NN ^3S_1 channels. Since no centrifugal force there, the system can be deeply bound. The decay into etaNN channel is energitically forbidden. The decay into piNN channel is also suppressed. For these reasons this quasibound state has so narrow width as 20 MeV in spite of the large width of the S_<11> resonance. In order to discover this quasibound state, we point out the signature of the state on observables for np-np,np-etad,gammad-np,gammad-etad and etad-etad processes.
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