Study On The Nature Of Ξ(1620) And Ξ(1690) States From Ξ_c~+→Ξ~-π~+π~+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,Ξ（1620）andΞ（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-waveπΞ（and its coupled channels）interaction was studied,where the excited hyperon stateΞ（1620）was reproduce dynamically,with the predicted spin-parity J^P=₂^1-.In this thesis,the s-waveπΞ（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 statesΞ（1620）andΞ（1690）are generated from the interaction,having the structure nature of meson-baryon molecular state.The main components ofΞ（1620）areπΞandˉKΛ,and the main component ofΞ（1690）isˉKΣ.Recently,the Belle Collaboration observedΞ（1620）andΞ（1690）production signals in theΞ^-π_Linvariant mass distribution of theΞ_c⁺→Ξ^-π⁺π⁺decay.In this thesis,this decay process is studied under the framework of Ch UA.Besides the background contributions,the contribution of theΞ（1620）andΞ（1690）resonances to theΞ^-π⁺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 theΞ（1620）andΞ（1690）states.The positions,widths and the relative strength of theΞ（1620）andΞ（1690）resonance states are determined by the following factors:πΞscattering in coupled chan-nels,and the dynamical generation mechanism and the structure nature of theΞ（1620）andΞ（1690）resonances.Therefore,the agreement between our theoretical results and the Belle experiment supports the molecular state picture of the exited hyperon resonancesΞ（1620）andΞ（1690）.