Study Of Heavy Baryon Properties From QCD Sum Rules

Since the first observation of a charmed baryon, ofΛ_c~+, was reported two yearsafter the J/ψdiscovery, a large number of heavy baryons have been discovered, par-ticularly in the first decade of this century. For the S-wave charmed baryons, the(1+)/2 antitriplet states (Λ_c~+,Ξ_c~+,Ξ_c~0) and the(1+)/2 and (3+)/2 sextet states ( c,Σ_c,Ξ_c) and( c ,Σ_c~+,Ξ_c~+) have been well established. Furthermore, several new excited charmedbaryon states have been observed by the BaBar, Belle and CLEO Collaborations, suchasΛ_c~+(2765),Σ_c~+ (2800),Ξ_c~0(2980). But of the corresponding bottomed baryons, onlytheΛ+b,Σb+,Σb+~+,Ξ_b~+, bhave been observed. With the running of Large Hadron Collider(LHC), more and more heavy baryon states will be discovered by the future experi-ments. Experimental progress calls for in-depth theoretical study. It is in this contextthat the present thesis is devoted to some research on certain properties of the heavybaryon states within the framework of QCD sum rules (SVZ sum rules and light-conesum rules).First, we analyze the J~P=(1+)/2 baryon states containing the quarks of the fourthgeneration and the charm or bottom quark within the framework of QCD sum rules.The existence of the fourth generation of quarks was predicted more than 20 years agobased on the flavor democracy arguments. The addition of the fourth generation ofquarks, which is one of the simple extensions of the standard model (SM), has manyimportant physical consequences. Particularly, some rare decay channels of heavy Bphysics are rather sensitive to the new physics beyond the standard model, and theaddition of the forth generation of quarks may have a notable impact on their branchingratios and CP asymmetries. Furthermore, researches show that the forth generation ofquarks can produce a significant effect on Higgs phenomenologies, and that when theyhave small enough mixing with the SM quarks, they could form new hadronic stateswith the ordinary SM quarks, and the parameterization of CKM matrix obeying thiscondition has been proposed. Therefore, it is necessary to investigate the propertiesof these new hadronic states theoretically and phenomenologically. We interpolate theJ~P=(1+)/2 new baryon states with Ioffe currents, and considering the perturbative andtwo gluon condensate contributions in the calculation after performing a parity isolationprocedure, we give the numerical results of their masses and pole residues. We alsoinvestigate the rations between the contributions from the negative parity and positive parity baryon states, and the results show that the contaminations from the negativeparity baryon states are comparatively large and the parity isolation procedure must bedone. Hope that our results of the masses obtained can be tested by the future Tevatornor LHC experiments, and the reasonable values of the pole residues obtained can betaken as basic input parameters for studying the revelent hadronic processes with QCDsum rules.Second, we analyze the vertexesΣ_QΞ_Q~+K~+ andΞ_QΣ_Q~+K~+ with light-cone sumrules. The charmed and bottomed baryons which contain one or two heavy quarks areparticularly interesting for studying dynamics of the light quarks in the presence of aheavy quark or heavy quarks. They serve as an excellent ground for testing predictionsof quark models and heavy quark symmetry. We parameterize the vertexesΣ_QΞ_Q~+K~+ andΞ_QΣ_Q~+K~+ with three tensor structures due to Lorentz invariance, and calculate thecorresponding three coupling constants within light-cone sum rules. For the determi-nation of the unknown values of the masses and pole residues, we make a study of SVZsum rules. We then obtain the numerical values of the strong coupling constants tak-ing into account all the uncertainties of the relevant parameters. These strong couplingconstants are basic parameters in describing the interactions among the heavy baryonstates; once reasonable values are obtained, we can use them to perform phenomeno-logical analysis. Our study show that heavy quark symmetry works well for the centralvalues of the strong coupling constant g1and g2...