Study On The D(?) Bound State In The Three-body Weak Decays Of Λ_b And B~-

As one frontier of physics,particle physics is to explore the ultimate structure and interactions of matter.Hadron physics is an important part of particle physics,mainly studying the internal structure and interactions of hadrons.In last decades,there are many resonances observed experimentally,especially the ones observed in the heavy quarkonium sector,which can not fit to the expectations of the conventional quark models.Study of these exotic hadrons is of great significances for improving our understanding of the internal structures of hadrons and the quantum chromodynamics.Since most exotic states lie around the thresholds of coupled channels,the hadronic molecules play a unique role in describing the internal structure of these states.This thesis focuses on the DD bound state X(3700),dynamically generated in the meson-meson interactions,as predicted by Oset et al..Although there are some hints of X(3700),the existence of this state needs to be confirmed,and the further theoretical studies on this state are crucial for the future experiments.In this thesis,we will study the X(3700)in the Λb→ ADD and B-→ K-ηηc decays.The Λb→ΛDD decay is investigated by considering the S-wave DD final state interactions,as well as the P-wave contributions from the vector mesonψ(3770).It is found that,in addition to the peak corresponding to the ψ(3770),an enhancement near DD threshold appears in the DD invariant mass distribution,which should be the reflection of the DD bound state.Moreover,the enhancement in the D0D0 invariant mass distribution is significantly stronger than the one in the D+D-invariant mass distribution.We hope that the Λb→ΛD0D0 decay can be studied experimentally,especially the partial wave analysis of this process,which could be helpful to test the existence of the DD bound state,and to deepen our understanding of the hadron-hadron interactions.We investigate the process of B-→ K-ηηc,by taking into account the S-wave contributions from the DD bound state and the intermediate K0*(1430)resonance.One can see a clear K0*(1430)signal in the K-η invariant mass distribution,and a clear peak corresponding to the DD bound state around 3730 MeV in the ηηc invariant mass distribution.We encourage our experimental colleagues to measure the B-→ K-ηηc process precisely,which is important for confirming the existence of DD bound state and testing its properties.In conclusion,by using the unitary coupled-channel approach,the final states invari ant mass distributions of the Λb bary on and B-meson three-body weak decays are calculated.Our results would provide a theoretical guidance for experimental study on the DD bound state,and is helpful to deepen our understanding of the strong interactions.