Improved One π Exchange Model And Heavy Meson-heavy Antimeson Bound States

The naive quark model was very successful in explaining the properties of traditional hadrons.In 2003,the Belle collaboration discovered X(3872),whose structure and properties are difficult to understand in traditional quark models.Subsequently,a lot of such exotic particles were observed in various experiments.Physicists proposed many possible structures,such as molecular states,compact multiquark states,hybrid states,etc.,discussed the properties of these exotic states,and made theoretical predictions on more exotic structures.The related problems are still the frontiers of the strong interaction study.In this thesis,we will perform a systematic study on whether bound states could exist in the meson-antimeson systems composed of D,D*,D0*,D1,D1’,D2*and their antiparticles.In these systems,some states with exotic quantum numbers JPC=0--,0+-,1-+,2+-,3-+ are allowed.Such quantum numbers are impossible for states composed of one quark and one antiquark.At present,it is still difficult to study hadron properties directly with QCD,the fundamental theory of strong interactions,because of its nonperturbative properties at low energy region.The studies of hadron properties are mainly based on effective theories and phenomenological models which are compatible with QCD.In the present study,we use the one-boson-exchange potential model to discuss the bound state problem in the heavy quark meson-antimeson systems.The involved interaction is described by the effective Lagrangian satisfying both the chiral symmetry and the heavy quark symmetry.In the limit that the mass of the heavy quarks goes into infinity,D and D*,D0 and D1’,and D1 and D2*form three degenerate doublets,which reduces the number of coupling constants.In this study,the meson with spin-2 is involved.The final potential may be complicated if one considers the coupled channel effects.Here,we introduce various"transition spin" operators to improve the Lagrangian and the form of potentials.The process to derive a potential is as follows:(1)write the scattering amplitude according to the effective Lagrangian,(2)introduce the transition spin operators to simplify the form,(3)get the non-relativistic potential function in the momentum space,and(4)obtain the potential in the coordinate space using the Fourier transform.As a preliminary study,we only consider the one-π-exchange potential.The final potential is similar to that of deuteron.Both of them contain the central part and the tensor part.Different from the deuteron,some potentials we obtain involve a new tensor operator.This operator could couple S-wave and G-wave channels.In addition,we also consider the effects on the matrix elements caused by the G parity constraint.In the numerical calculations,we consider the bound state problem in both the single channel case and the multi-channel case.The results indicate that:(1)D1(?)1’,D*(?)1’,D’(?)1’,D*(?)1,D1(?)1’,D*(?)2*could form the bound states with exotic JPC,and their IG(JPC)are 0-(0--),0-(0--),0+(1-+),1+(0--),0-(0+-),0+(3-+).(2)In the bound states 0-(0+-)D1(?)1’,0-(3+-)D1(?)2*,0-(1+-)D1’(?)2,0+(1++)D1’(?)2*,0+(2++)D1’(?)2*,0-(1--)D*(?)1,0-(2--)D*(?)1 and 0+(3-+)D*(?)2*,the coupled channel effects are crucial;(3)For most of the states with exotic quantum numbers,the coupled channel effect is not so important.Besides,we also consider the possible decay channels of the molecular states.