| In 1964,Gell-Mann and G.Zweig put forward the quark model independently which was the fundamental breakthrough for the understanding of the substructures of matter,originally,only the u,d and s quarks are proposed in the quark model,with the development of theory and experiment,c,b and t quarks were included in gradually.In 1968,SLAC National Accelerator Laboratory found the scaling independence in the electron-proton deep inelastic scattering(DIS)experiment,J.D.Bjorken proposed that the electron acts with lots of free particles which have no mutual interaction in the DIS,that is,the quark interaction becomes weak and has the so called asymptotic free characteristic under the precondition of large momentum transmission.Based on the asymptotic free characteristic derived from the DIS experiment,applying the SU(3)color gauge theory as the quantum field theory of the strong interaction,D.J.Gross,H.D.Politzer and F.Wilczek built Quantum Chromodynamics(QCD)which is the basic theory to study the strong interaction.Since no free quark has ever been found,it is believed that the interaction between the two quarks should become stronger with the increment of their distance which is the so called quark confinement.Since the discovery of X(3872),many charmonium-like and bottomonium-like states were observed,their masses and decays are different from the baryons and mesons which indicate that they have more complicated structures,these exotic states become good candidates for the hybrid states,tetraquarks,tetraquark molecules,pentaquarks,pentaquark molecules,etc..Recently,researches about these exotic states via the theory based on the QCD become the hotspot of the particle physics.The typical theoretic tools contain the potential model,quark model,lattice QCD,QCD sum rules,etc..In 1979,Shifman,Vainshten and Zakharow set up the QCD sum rules,the basic assumption is to apply the vacuum condensates such as the quark condensate,gluon condensate etc.to describe the physical states and parameterize them based on the experimental data.Technically,the QCD sum rules uses the interpolating current to couple the related state,and conducts the operator expansion(OPE)at the QCD side for which the vacuum condensates embody the non-perturbative effect.Borel transformation is applied to depress the contribution of vacuum condensates with high dimensions,the excited states and continuum state.Then,applying the quark-hadronic duality,one can find the QCD sum rules for the considered states.Now,the QCD sum rules is widely used to study the particles’ masses,decays,transition form factors etc..In this thesis,the following aspects are studied in detail via the QCD sum rules,1.Eight color singlet-singlet currents with the JP=0+,0-,1+ and 1-,namely,the scalar,pseudoscalar,pseudovector and vector currents,are constructed to study the ΛcΛc dibaryons and ΛcΛc baryoniums.The current with the JP=0+is discussed in a detailed way for the contribution of all kinds of condensates under dimension 16,and the highest order of the truncation of O(αsk)is k=3,results of these discussions provide the reference for the selection of vacuum condensates of the states studied in the present article.Moreover,the correlation function of ΛcΛc dibaryon with the JP=1+ is equal to zero,thus we calculate the masses and pole residues of the seven ΛcΛc dibaryons and ΛcΛc baryoniums except the ΛcΛc dibaryon with the JP=1+.2.Eight color singlet-singlet currents with the JP=0+,0-,1+ and 1-are constructed to couple with the related ΣcΣc dibaryons and ΣcΣc baryoniums.The highest dimension of the considered vacuum condensates is 16 and the orders of the truncation of O(αsk)are kept as k≤1.This study indicates that there is no ΣcΣc dibaryon state with the JP=1+.Results show that,for baryonium states with the JP=1-,0+ and ΣcΣc dibaryon with the JP=0+,they may be the molecular states.3.Eight color singlet-singlet currents with the JP=0+,0-,1+ and 1-are constructed to couple with the related ΛcΣc and ΛcΣc dibaryons.The highest dimension of vacuum condensates is 16 and the orders of the truncation of O(αsk)are kept as k≤1.Results of this work show that there are three possible molecular states,they are ΛcΣc dibaryon with the JP=1+,ΛcΣc dibaryons with the JP=0and 1-respectively.4.Eight currents of the isospin eigenstates are constructed to study the pentaquark molecular states.The vacuum condensates of the OPE are considered up to dimension 13 and the orders of the truncation of O(αsk)are kept as k≤1.It shows that the states with high isospin have relatively large value for their masses,detailed numerical results of this work support assigning Pc(4312),Pc(4380),Pc(4440)and Pc(4457)as the DΣc with the IJP=(1/2)(1/2)-,DΣc*with the IJP=(1/2)(3/2)-,D*Σc with the IJP=(1/2)(3/2)-and D*Σc*with the IJP=(1/2)(5/2)-pentaquark molecules,respectively.As for the other four pentaquark resonance states,their masses are slightly higher than the thresholds of the related meson and baryon.5.Eight currents of the isospin eigenstates are constructed to study the pentaquark molecular states with strangeness.The vacuum condensates of the OPE are considered up to dimension 13 and the orders of the truncation of O(αsk)are kept as k≤1.This work supports assigning Pcs(4459)as the DΞc*pentaquark molecule,among the considered states,those ones with low isospin have the masses lower than the thresholds of the meson and baryon,whereas the ones with high isospin are above the thresholds of the related meson and baryon.6.Ten currents of the isospin eigenstates are constructed to study the newly discovered Pcs(4338).The vacuum condensates of the OPE are considered up to dimension 13 and the orders of the truncation of O(αsk)are kept as k≤1.This work supports assigning Pcs(4338)as DΞc pentaquark molecule with the IJP=0(1/2)-,what’s more,results show that Pcs(4459)may be D*Ξc pentaquark molecule with the IJP=0(3/2)-. |
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