Dynamical Studies Of The Heavy Molecular States

In the conventional quark model, the hadrons are classified as q qˉmesons and qqqbaryons. In the past ten years, many charmonium-like or bottomonium-like states wereobserved experimentally. However, some of the charmonium-like or bottomonium-like states, such as X（3872）, Z_b（10601） and Z_b（10650）, do not fit into the conventionalcharmonium （ccˉ）or bottomonium （bˉb）. Therefore, searching for the exotic states beyondthe naive quark model has become a hot topic. So far, the proposed exotic candidatesinclude the hadronic molecules, guleball, hybrid and multiquark states. This thesisfocuses on the molecules composed of the heavy flavor mesons or baryons.In the INTRODUCTION and Chapter2, I briefly introduce the experimental statusand the theoretical approaches in the study of the heavy flavor physics at the low energyregion. Although lots of exotic hidden-charm states have been observed experimentally,most of them have not been confirmed. Moreover, even for those well-establishedstates, their inner structures are not clear. It is still a big challenge for us to understandthese exotic states. At present, the widely used theoretical tools at the low energy regioninclude the QCD sum rule, the chiral perturbation theory, the chiral quark model andthe one-boson-exchange model. I adopt the one-boson-exchange formalism.Jaffe proposed the H-dibaryon within the MIT bag model in1970s. The quan-tum numbers of the H-dibaryon are strangeness S=-2, spin-parity J^P=0⁺. Lotsof efforts have been spent on the study of the H-dibaryon. However, it has not beenestablished. It was also found that the ΛΛ system with the same quantum numberdoes not form a bound state either. Here, I extended the analysis to the heavy flavorsector. In Chapter3, I investigated the possible Λ_cΛ_c, Ξ_cΞ_c, Σ_cΣ_c, Ξ_cΞ_candΩ_cΩ_cmolecular states. The numerical results indicate that ΞcΞc[1（0⁺）,0（1⁺）], Σ_cΣ_c[1（1⁺）],Ξ_cΞ_c[1（0⁺）,0（1⁺）] andΩ_cΩ_c[0（0⁺）] might be good molecule candidates. However,Λ_cΛ_c[0（0⁺）] dose not form a bound state without the coupled-channel effect in the fla-vor space. For the baryon-antibaryon systems, the one-boson-exchange model dosenot work well due to the annihilation of the system at short-range. I also performed acoupled-channel analysis of Λ_QΛ_Q（Q=c, b）. I found that not only the positive-parity state Λ_QΛ_Q[0（0⁺）] but also the negative-parity states Λ_QΛ_Q[0（0）,0（1）] could formbound states because of the coupled-channel effects in the flavor space.Despite huge efforts, there is still no consensus on the interpretation of X（3872）.In Chapter4, I performed a coupled-channel analysis of X（3872） and calculated itsisospin breaking. I considered the S-D mixing, the charged D^*mesons, the couplingof DDˉ^*to D^*D^*, and the isospin breaking arising from the mass difference betweenthe charged and the neutral D^*mesons. I noticed that the total potential roughlyequals to the one-pion-exchange potential since the interaction of the heavier rho andomega exchange cancel each other significantly. Besides, taking the phase space dif-ference arising from the different ρ0and ω mass, I calculated the ratio of the branchingfractions R=B（X�'π⁺π^-π⁰J/ψ）/B（π⁺π^-J/ψ）, which was consistent with themeasurements of Belle and BABAR.In2002, the SELEX Collaboration observed the doubly-charmed baryon Ξ_cc. Al-though, the results are not confirmed by Belle and BABAR collaborations, it is still veryinteresting to study such system which might be produced by the future high-energycolliders. The molecular states with double charm provide another insight to studysuch a system. In Chapter5, we performed a coupled-channel analysis of the possibleD^*D^*,Bˉ^* Bˉ^*and D^* Bˉ^*molecular states within the one-boson-exchange for-malism. I predicted some interesting states which might be searched for in the futureexperiments.