Lattice Calculation Of Radiative Transition Decay Width Of Charm Quark Contained Mesons

In recent years,particle physics has developed rapidly,some basic particles and the interaction between them have aroused extensive research interest.There are four interactions in nature,i.e.strong interaction,electromagnetic interaction,weak interaction and gravity interaction.Quarks are elementary particles involved in strong interactions.Charmed meson is a meson which composed of positive and negative quarks,one of which is charm quark.Its different orbits and spin angular momentum combination constitute different ground and excited states of the meson,forming a family of particles.Quantum chromodynamics（QCD）is a basic theory that describes the strong interaction.Lattice QCD is a basic theory describing strong interaction from the first principles of QCD.In this thesis,we studied the internal structure of the properties for the charmed meson,in particular,the radiative transition decay width of charmonium.The theory of Lattice QCD is used in this thesis,we used the N_f=2 Twisted Mass configurations to calculate the mass spectrum of X_c1 and J/ψ,and we verified the dispersion relation on the lattice.We calculated the form factor of radiative transition of X_c1→J/ψγ,and extracted the decay width of this physical processes.The explicit content of this thesis is following:（1）We studied the mass spectrum and dispersion relationship of X_c1 and J/ψ based on N_f=2（u and d quark）Twisted Mass configurations which generated by the European Twisted Mass collaboration（ETMC）.We simulated the two-point correlations corresponding with momentum zero and other momenta.We extracted the mass spectrum and energies with different momenta using these two-point correlations.According to these physical quantities,we fitted the Z factor in the dispersion relation.In this calculations,we used anti-periodic boundary conditions in two-point correlations,and extracted the energies of the states.When the momentum is zero,the energy is equal to the mass of meson.We fitted the mass of X_c1 and J/ψ.We obtained the fitted dispersion relation and shown the relation in figures,and obtained the fitted constant Z factor.（2）We calculated the radiative transition decay width ofX_c1→J/ψγ in this thesis.We used N_f=2 Twisted Mass gauge configurations to calculate the radiative transition decay width ofX_c1→J/ψγ.In order to improve the momentum space resolution,we use the twisted boundary condition to calculate the corresponding correlation function,which effectively controls the systematic error of the physical quantities.In the same time,in order to enhance the overlap of the operator and vacuum,we considered the effect for the mixing of parity to calculate the form factors and decay width of radiative transion processes.The transion decay width of various charmonium is related to the matrix element of the electromagnetic vector current and can be extracted by the three-point correlation function.It is calculated by the ratio of three-point correlation function to two-point correlation function.The corresponding of form factors to the decay width is obtained by the relationship of matrix element and form factor.