The Study Of Coupled Channel Effects In The Decays Of Exotic Hadronic States

Quantum Chromodynamics ?QCD? is regarded as a theory describing the strong interaction.In the high energy region, the perturbative theory still works due to the small effective coupling.In the low energy region, the perturbative theory does not work since the running coupling constant becomes larger. As a result, the methods of phenomenology become very important.The study of exotic hadron states physics plays an important role on hadron physics as an important probe for understanding the nature of QCD in both perturbative and non-perturbative regime. In recent years, the BES-?, Belle, BABAR and LHCb collaborations observed many new hadron resonances. In this thesis, we apply model for intermediate meson loops to study coupled-channel effects in the productions and decays of the some exotic hadron states. The article mainly includes the following two aspects:1. We study the isospin conserved hidden bottomonium decay of X_b ? ??1S?? , where X_b is taken to be the counterpart of the famous X?3872? in the bottomonium sector as a candidate for the meson-meson molecule. Since it is likely that the X_b is below the ???B*threshold and the mass difference between the neutral and charged bottom meson is small compared to the binding energy of the X_b, the isospin violating decay mode X_b???nS??+?-would be greatly suppressed. We use the effective Lagrangian based on the heavy quark symmetry to explore the rescattering mechanism of X_b???1S?? and calculate the partial widths.Our results show that the partial width for the X_b???1S?? is about tens of KeVs . Taking into account the fact that the total width of X_b may be smaller than a few MeV like X?3872?,the calculated branching ratios may reach to orders of 1O-2. These hidden bottomonium decay modes are of great importance in the experimental search for the X_b particularly at the hadron collider. Also, the associated studies of hidden bottomonium decays X_b???nS??,??nS??,BB?may help us investigate the structure of X_b deeply. The experimental observation of X_b will provide us with further insight into the spectroscopy of exotic states and is helpful to probe the structure of the states connected by the heavy quark symmetry.2. To validate the molecular description of the observed Z_b?10610?/Z_b?10650? and Z_c?3900?/Z_c?4025? , it is valuable to investigate their counterparts, denoted as Z_Qv^?'? in this work, and the corresponding decay modes. In this work, we present an analysis of the Z?'?QV using falvor symmetry. We also use the effective Lagrangian based on the heavy quark symmetry to explore the rescattering mechanism and calculate the partial widths for the isospin conserved channels Z?'?QV??_QV. The predicted partial widths are of an order of MeV for Z_QV??_QV,which correspond to branching ratios of the order of 10^-210^-1.For Z'_QV??_QV,the partial widths are a few hundreds of Ke V and the branching ratios are about 310-.Future experimental measurements can test our predictions on the partial widths and thus examine the molecule description of heavy quarkoniumlike exotic states.