Research On The Mass Spectrum Of Tetraquark Molecular States With QCD Sum Rules

Since the discovery of the X(3872)in 2003,a number of exotic states have been observed by the international collaborations,they cannot be accommodated in the traditional quark models,and are excellent candidates for the multiquark states.The multiquark states have attracted a lot of researchers at home and abroad and become an international hot subject.Shifman,Vainshtein,Zakharov et al.[1-3]proposed the QCD sum rules in the late 1970s,which considered the influence of non-perturbative effect in calculation by phenomenologically introducing vacuum condensates parameters,and developed this approach into an effective non-perturbation QCD method,which is usually called SVZ sum rules.QCD sum rules approach has been applied extensively in particle physics,and has been become a powerful theoretical tool in studying the multiquark states and has given a number of successful descriptions.In the present work,we introduce the theoretical background and research methods of this study firstly.We briefly introduce the basic principle of QCD,which has the full name of Quantum Chromodynamics.We also briefly introduce hadron physics through previous experimental and theoretical studies,and discuss the four important internal symmetries which are associated with the color degree of freedom,the flavor degree of freedom,the spin degree of freedom and the orbital degree of freedom,gluon degree of freedom,and heavy quark symmetry.Then we introduce the principle and the specific process of the research method of this work,which is QCD sum mles,and elaborate on the two criteria of QCD sum mles,that is,the convergence of the operator product expansion and the pole dominance.After that,we construct the color-singlet-color-singlet type four-quark currents to investigate the Ds(?)s1 and Ds*(?)s0*tetraquark molecular states with the JPC=1--and 1-+via the QCD sum rules.We introduced two-point correlation functions and accomplish the operator product expansion up to the vacuum condensates of dimension 10 consistently.We take account of the SU(3)mass-breaking effects to investigate the masses of tetraquark molecular states with strange quark and adopt the modified energy scale formula to choose the best energy scales of the QCD spectral densities by considering the energy-scale dependence of QCD sum rules.Then we extract the masses and pole residues of the tetraquark molecular states in the suitable Borel windows which satisfy the two fundamental criteria of the QCD sum rules and obtain satisfactory results.Our reliable calculation provides a reliable theoretical basis for international high-energy physics experiments,a necessary theoretical basis for our understanding of multi quark states,and improves people’s understanding of QCD dynamics at low energy.