Studies On Mutiquark States And Heavy Mesons In The Framework Of QCD Sum Rule

QCD sum rule is one of the most important nonperturbative methods. It was usedwidely to study the hadron spectrum and their decay properties since its invention. Inthis thesis we first present the formalism of QCD sum rule approach and its later devel-opment, with the emphasis on the different aspects of SVZ sum rule, finite energy sumrule and light cone sum rule. We discuss the classification of heavy meson spectrumunder heavy quark effective theory (HQET) and the application of QCD sum rule inHQET. Then we apply the QCD sum rule method to study one special kind of muti-quark system and excited heavy mesons. We get the following results:(1) The interesting state X(1600) with J^PCI^G = 2⁺⁺2⁺ can not be a conventionalq(q|-) meson in the quark model. Using a mixed interpolating current with different colorconfigurations, we investigate the possible existence of X(1600) in the framework ofQCD finite energy sum rules(FESR). We obtain a stable FESR with converged OPE andreasonable threshold parameter. The mass obtained is consistent with the experimentalvalue. Our results indicate that coupled channel effect may be quite important in themultiquark system. We propose several reactions to look for this state.(2)With the identification of (D_sJ(2317),D_sJ(2460)) as the (0⁺, 1⁺) doubletin HQET, we derive the light cone sum rules for the coupling of eta meson withD_sJ(2317)D_s and D_sJ(2460)D_s^*. Throughη－π⁰ mixing we calculate their pionic de-cay widths, which are consistent with the experimental values (or upper limits). Com-bining the radiative decay widths derived by Colangelo, Fazio and Ozpineci in the sameframework, we conclude that the decay patterns of D_sJ(2317, 2460) strongly supporttheir interpretation as ordinary c(s|-) mesons.(3)In the leading order of HQET, we first extract the binding energy (Λ|-) and decayconstants of the D wave heavy meson doublets (1^－, 2^－) and (2^－, 3^－) with the two pointsum rule. Then we study their pionic (Ï€,K,η) couplings using the light cone sum rule,from which the leading order binding energy (Λ|-) can also be extracted. We then calcu-late the pionic decay widths of the strange/non-strange D wave heavy D/B mesons anddiscuss the possible candidates for the D wave charm-strange mesons. Further experi- mental information, such as the ratio between D_sηand DK modes, will be very usefulto distinguish various assignments for D_sJ(2860, 2715).