Study On Double Heavy Tetraquark With Negative Parity

In recent years,a large number of unknown particles such as X,Y and Z have been discovered in experiments.Compared with the conventional quark-antiquark mesons and three-quark baryons,these particles may be composed of more than three quarks,so the multiquark state has rised people's widespread attention.In 2015,the LHCb collaboration observed two hidden-charm pen-taquark states in the pJ/? decay channel,Pc(4380)and Pc(4450).However,it was not until 2017 that LHCb discovered the double baryon ?cc++ with a mass of 3621.40±0.78MeV.After ?cc++,people began to take seriously the existence of open-flavored tetraquark states as hadrons.This thesis uses the QCD sum rules to study the mass and weak decay of a class of negative-parity,open and hidden bottom/charm tetraquark states.The main contents of this study are as follows:The first chapter first briefly introduces some basic features of Quantum Chromodynamics(QCD),perturbation QCD(pQCD)method and some known non-pQCD methods,including QCD sum rules,QCD factorization,QCD resum-mation,Lattice QCD(LQCD),chiral perturbation theory,QCD large-N expan-sion,etc.The last part of this chapter discusses the relevant background of the tetraquark states.In Chapter2,we introduce several key steps of the QCD sum rules method,and explain how to construct the correlation function,how to construct the current of tetraquark,operator product expansion(OPE)and QCD vacuum con-densates,dispersion relation and Borel transformation.Then,several sources of errors in the calculation of the QCD sum rules are described.In Chapter3,we use the QCD sum rules method to calculate the masses of the doubly heavy tetraquark state with I=1/2,1,JP=1+,and estimate the weak decay width of the double-bottom tetraquark state.The same method is applied to study the hidden charm tetraquark states cqcq and the hidden bottom tetraquark state bqbq.The mass and decay width of the tetraquark state with JPC=0++ are computed by constructing currents for the scalar diquark-antidiquark configuration.Chapter4 gives overall summary of the thesis and gives the prospect of future work.