Study On Nucleon Resonances In Meson Photoproductions

The properties of the hadrons are deterrmined by the non-perturbative properties of QCD in the low-energy region and the studys on the properties of the hadrons,such as the hadronic mass spectrum,the hadronic productions and the hadronic decays,are of great significance in the fully understanding of the non-perturbative nature of QCD.Due to the non-perturbative nature of QCD,non-perturbative methods and QCD-inspired phenomenological models have been developed to the sdudy of hadron states in the non-perturbative region.The quark model has been successful in the arrangement of the hadron excitations(resonances)and explaining many properties of the hadron excitations.However,the quark model also faces some unavoidable problems such as the "inversed masses" problem,the "missing resonances" problem and the exotic hadronic states problem.The effective Lagrangian approach has been widely applied to the study of the hadronic productions and the hadronic decays.It has been applied to study of the hadronic productions and the hadronic decays by constructing the vertex effective Lagrangian density under requirements of the elementary symmetries in the hadron level with the assumption that the freedoms of the quarks inside the hadron have been frozen.The information on resonances has been mainly extracted from the data of?N scattering experiment and the ?N photoproduction experiment.Some resonances that predicted in theoretical analyses might have escaped from detections in ?N scattering experiment and ?N photoproduction experiment due to their small coupling to the ?N channel and thus the study on hadron resonances in reaction processes with non-?N final state will be of necessity and significance.In this thesis,we focus on the study of the nucleon resonance in meson photoproductions based on the effective Lagrangian approach.It is well known that,the cross-section data alone is far from being sufficient to uniquely determine the resonance contents in mson production reactions,and the data on spin polarized observables imposses addictinal constraints in the constructions of the reaction amplitude.And thus,we expect better extraction of the resonance information in meson photoproductions and better understanding of the reaction mechanisms by including the data on spin polarized observables in addiction to the data on cross section in our analyses.This thesis includes the following analyses of three meson photoproduction processes(1)Nucleon resonances in ?p??p.The most recent high-precision data on spin observables ?,T,P',E,F and H reported by the CLAS Collaboration together with the previous data on differential cross sections and spin-density-matrix elements reported by the CLAS,A2,GRAAL,SAPHIR and CBELSA/TAPS Collaborations for the reaction ?p??p are analyzed within an effective Lagrangian approach.The reaction amplitude is constructed by considering the t-channel ? and ? exchanges,the u-channel nucleon and nucleon resonances exchanges,the u-channel nucleon exchange and the interaction current.The latter ensures that the full photoproduction amplitude is gauge invariant.It is shown that all the available CLAS data can be satisfactorily described by considering the N(1520)3/2-,N(1700)3/2-,N(1860)5/2+,N(1875)3/2-,N(1895)1/2-and N(2060)5/2-resonances in the s-channel.The parameters of these resonances are extracted and compared with those quoted by PDG.(2)Nucleon resonances in ?p?K*?.In the work[Phys.Rev.C 96,035206(2017)],the high-precision differential cross-section data for ?p?K*? reported by the CLAS Collaboration has been analyzed within an effective Lagrangian approach.It was found that apart from the t-channel K,K*and ? exchanges,the u-channel A,? and ?*exchanges,the s-channel N exchange and the interaction current,one needs to introduce at least two nucleon resonances in the s channel in constructing the reaction amplitudes to describe the cross-section data.One of the needed resonances is N(2060)5/2-,and the other one could be one of the N(2000)5/2+,N(2040)3/2+,N(2100)1/2+,N(2120)3/2-and N(2190)7/2-resonances.In this paper,we further include in our analysis the data on spin density matrix elements for K*meson reported recently by the CLAS Collaboration,with the purpose being to impose further constraints on extracting the resonance contents and to gain a better understanding of the reaction mechanism.It turns out that with the new data on spin density matrix elements taken into account,only the set with the N(2060)5/2-and N(2000)5/2+ resonances among those five possible solutions extracted from the analysis of the differential cross section data can satisfactorily describe the data on both the differential cross sections and the spin density matrix elements.Further analysis shows that this reaction is dominated by the t-channel K exchange and s-channel N(2060)5/2-and N(2000)5/2+exchanges.(3)Nucleon resonances in ?p?K?(1520).The data on differential cross sections reported by the CLAS Collaboration together with the data on differential cross sections and photo-beam asymmetries ? reported by the LEPS Collaboration for the ?p?K?(1520)reaction have been analyzed within an effective Lagrangian approach.In addiction to the t-channel K and K*exchanges,the u-channel A exchange and the s-channel nucleon and nucleon resonance exchanges,the interaction current was introduced to ensure the full amplitude gauge invariant.The t-channel Regge contributions have been included in gauge-invariant manner within a hybrid framework.Numerical results shows that the experimental data can be reproduced by including at least one resonance in the s channel and the needed resonance could be either the N(2060)5/2-or N(2120)3/2-.The predictions of the target asymmetry T turn out to be quite different for the results of including the N(2060)5/2-or N(2120)3/2-which can be distinguished by further measurements of spin polarized observables.