Study Of Hadronic Molecular States In A Quasipotential Bethe-salpeter Equation Approach

It’s a great feat in the history of physics that people have found all the fundamental particles in the Standard Model of particle physics, after the observation of Higgs boson. However, there are still many problems to be solved for hadron structure. According to the traditional quark model, a meson is composed of a pair of quark and antiquark and a baryon is composed of three quarks or three antiquarks. In the past few years, a series of the XYZ states beyond traditional quark model have been observed experimentally. Those exotic states might be the multiquark states for which people are looking in the last decades. In view of the mass of exotic state near the threshold of two hadrons, it’s reasonable to interpret exotic states as molecular states as deuteron. The phenomenal model is a powerful tool to study the properties of exotic states for complexity of strong interaction in non-perturbative region. In our work, the one-boson-exchange(OBE) model is adopted to explore the relation between exotic states and hadronic molecular states through solving a quasipotentional Bethe-Saltpeter equation.This thesis firstly introduced the quasipotential Bethe-Salpeter equation approach in the one-boson-exchange model, then the studies of interactions of several hadronhadron systems in the quasipotential Bethe-Salpeter equation approach will be presented. In the first part, we study the Y(4274) as the DsˉDs0(2317) molecular with the Bethe-Salpeter equation for the vertex. And with all parameters considered, a loose bound state can be found when solving the Bethe-Salpeter equation, the Y(4274) can be explained as a molecular state from the DsDs0(2317) interaction. In the second part, we study the octet meson and baryon interaction with strangeness S =-1, the two-pole structure related to the Λ(1405) can be reproduced. The lower one of the two poles originate from the πΣ interaction as a resonance and the higher one is from the ˉKN interaction as a bound. In the third part, we investigate the possible molecular state from the K ˉK* interaction. Considering both the one-boson exchange and the Weinberg-Tomozawa term, a pole with quantum number IG(JPC) = 0+(1++) canbe produced and related to the f1(1285). Another two molecular bound states with0-(1+-) and 1-(1++) are also produced from the K ˉK* interaction. It needs more studies to clear the relation between those two poles and experimentally observed states h1(1380) and a1(1420). We can also find that the Weinberg-Tomozawa term is more important than the one boson exchange, and can not be reduced from the vector meson exchange.