Study On The Nature Of ?(1620) And ?(1690) States From ?_c~+??~-?~+?~+Decay

The properties and the internal structures of hadrons,the rules of transformation be-tween particles and the strong interaction are main topics of hadron physics.Most hadron states are well explained by the traditional quark model.But there exists experimentally some hadron states whose properties cannot be explained well with the traditional quark model.Among them,two excited hyperon states,?(1620)and?(1690),are investigated in this thesis.They are considered to be candidates of exotic hadron states,since their masses,widths,decay branching ratios and other properties cannot be well described by the traditional quark model.As an effective field theory of low energy QCD,the chiral unitary approach(Ch UA)described successfully the meson-meson and meson-baryon interactions at low energy region.Hadron states can be generated dynamically from the interactions in the Ch UA,having the structure nature of hadronic molecular state.In the work of the Ramos et al.,the s-wave??(and its coupled channels)interaction was studied,where the excited hyperon state?(1620)was reproduce dynamically,with the predicted spin-parity J^P=₂^1-.In this thesis,the s-wave??(and its coupled channels)interaction is restudied,using another renormalization method,three momentum cutoff,to deal with the divergency of propagator loop function.Both the excited hyperon states?(1620)and?(1690)are generated from the interaction,having the structure nature of meson-baryon molecular state.The main components of?(1620)are??and?K?,and the main component of?(1690)is?K?.Recently,the Belle Collaboration observed?(1620)and?(1690)production signals in the?^-?_Linvariant mass distribution of the?_c⁺??^-?⁺?⁺decay.In this thesis,this decay process is studied under the framework of Ch UA.Besides the background contributions,the contribution of the?(1620)and?(1690)resonances to the?^-?⁺invariant mass distribution is calculated.Finally,the theoretical results are compared with the Belle experimental results.The research results of this thesis show that the theoretical results are in good agree-ment with the Belle experiment in the energy range[1550,1700]Me V of the?(1620)and?(1690)states.The positions,widths and the relative strength of the?(1620)and?(1690)resonance states are determined by the following factors:??scattering in coupled chan-nels,and the dynamical generation mechanism and the structure nature of the?(1620)and?(1690)resonances.Therefore,the agreement between our theoretical results and the Belle experiment supports the molecular state picture of the exited hyperon resonances?(1620)and?(1690).