Meson-antimeson States With Exotic J^PC In One-pion Exchange Model

The naive quark model has achieved great success for our understanding about hadrons in the early age. However, it seems not complete from modern prospective. On one hand, QCD, as the fundamental theory of the strong interac-tion does not forbid the existence of other colour singlet states such as gluon-ball, hybrid state and tetraquark state. On the other hand, experiments have found some hadrons which are hard to understand in naive quark model, such as the charged charmoniumlike states. Because of the non-perturbative properties of QCD, we have to use phenomenological methods such as QCD sum rule, chiral perturbation theory, meson-exchange models and so on. Meanwhile, one cannot determine all the phenomenological parameters because of the lack of experimen-tal data. Therefore, we could not fully understand the structures of such exotic hadrons so far. If the exotic states really exist, they may have the quantum num-bers which can’t exist in naive quark model, that is, the exotic quantum number. So the search of hadrons with exotic JPC is another way to find exotic states.In this thesis, we study possible molecular states in one-pion exchange model by assuming that the one-pion exchange dominates the long range interaction. We focus on the systems with exotic JPC which can’t be formed by a quark and an antiquark. Explicitly, the involved mesons are D, D*, D*0, D’1, D1, and D*2 and the possible exotic JPC are 0--,0+-,1-+,3-+. After reformulating the effective Lagrangian with "transition spin", we get the amplitude for one pion exchange. Then we get the interactive potential in non-relativistic limit. Notice that the pion is not a point particle, we include a form factor with cutoff parameter A. By solving Schrodinger’s equation we get the binding energy. Because of the insufficiency of experimental data, we estimate A in a reasonable range.Firstly, we omit the coupled channel effects, that is, only S-wave interaction is considered and study possible exotic states. Then we include the coupled channel effects. Now, the possible molecular states are DD*0(00--), D*D’1(00--,01-+), D*D1(10--,01-+), D1D’1(00+-), D*D*2(11-+,01-+). The result also shows that (1) the molecular states are S-wave dominated, (2) the coupled channel effect is nontrivial, and (3) the binding energy is sensitive to A.Similarly, we also study the B meson system which is the partner of D meson according to the heavy quark flavour symmetry. The heavier mass of b quark in reality makes the molecule easier to form. We also discuss the dominate hidden-charm (hidden-beauty) decay channels. The molecular system can be confirmed from its decay channel experimentally.