Decay Of Hybrid State In Quark Model With Constituent Gluon

The existence of some exotic mesons such asπ1,(Jpc=1-+), f0(980)(Jpc=0++) were already established experimentally, while their nature has been a puzzle for decades with little real progress on their understanding. The mass spectrum showed richer structures and various models came out to explain the structural properties of these exotic mesons. Most people believe that the structures of these exotic mesons are far beyond the naive qq picture, because they have quantum numbers not allowed by of qq states or ground states of qq states.In this thesis, we shall focus on the exotic mesons as hybrid states (qqg) within the framework of relativistic quark model with constituent gluon. The wave function have been constructed, and by fixing all the free parameters such as strong coupling constant g, the size parameters of the orbital wave functionsμ, the decay widths of the exotic hybrid states in their dominant channels have been calculated. Being compared with the existing experimental data, the present results indicate that the decay width ofπ1 (1400) as hybrid states is suppressed in the phase space, whileπ1,(1400) is claimed decaying intoπηexperimentally, and therefore,π1,(1400) may not be a hybrid state, whereas the calculated decay widths of f0(980) as hybrid states is within the range from 40 to 100 MeV given by PDG. This result of f0(980) is also close to those given by other assumptions that fo(980) as the p-wave qq state and KK molecule state.This thesis consists of three parts:In the first part, we give a brief review of study in hadrons'structure, the experimental situation and theoretical predictions of some exotic mesons. In the second part, we will introduce the hybrid model, a quark model with constituent gluon. In particular we introduce how to construct the wave function of normal mesons and hybrids, with an emphasis on relativistic effects, including spin-orbit coupling and phase space modification. In the third part, we calculate and analyze the decay widths ofπ1, (1400), f0(980) etc as some hybrid states compared with the experimental data.