Theoretical Investigations On The Photoproduction Of Light Scalar Mesons

Over the past half century,with the continuous development of experimental methods and theoretical methods,people have gradually realized that hadrons are not elementary particles.Gell-Mann and Zweig independently proposed that hadrons consist of quarks.The traditional quark model can give a reasonable explanation to most hadrons,especially for the pseudoscalar mesons and vector mesons.But for scalar mesons like f0 and a0,there are still a lot of disputes about their quark constituents.For this reason,Nowadays,a variety of non-perturbative methods have been developed:lattice theory,QCD sum rule,Dyson-Schwinger equation,etc.Due to the complexity of the non-perturbative QCD theory itself,it is very difficult to solve the low-energy problem from the first principle completely.Therefore,it is still of great significance to further develop the phenomenology method in low-energy region.First,this thesis will briefly introduce the history of the discovery of elementary particles and the related physical models and theories established on it.The main content of this research include:Firstly,based on the effective Lagrangian approach,the production of a1(1260)axis vector meson in Kp scattering is studied in detail.In this process,we mainly considering the production mechanism of the meson-resonance model.By working out the effective Lagrangian of the different interaction vertices in the production process of a1(1260),we can get the corresponding vertex function.The scattering amplitude of the K-p?a1(1260)? process then can be written using the Feynman rule,and the total cross section of this process is obtained.Based on the previous calculation,we allow the a1(1260)in the final state of the two-body process further decay into three ? mesons,and in the same time give the prediction of the total cross section.Thereafter,the photoproduction process of the f0(980)and f0(1500)scalar mesons were also studied in detail using the same method mentioned above.The differential cross sections d?/dt of the ?p?f0p two-body process,the invariant mass distribution of the f0 meson resonance of the three-body process,and the invariant mass distribution at different range of the Mandelstam variable t were obtained successively.These results has been compared with the measurement of experiment separately.From this,we conclude that the photoproduction of f0(1500)can be described by the t-channel process alone fairly well.It might imply that the main constituent of f0(1500)is not glueball.For f0(980),though t-channel process can explain the experimental data of differential cross section,its prediction of invariant mass distribution deviated from experiments significantly.We believe contribution from other channels cannot be ignored.More accurate experimental data in the future would be a great help to further determine contribution of each channels.