| Since Jaffe’s first prediction of the dibaryon:H particle in 1977, there have been many efforts both theoretically and experimentally to search for dibaryons. However, so far no dibaryon has been confirmed by experiments. Recently the CELSIUS-WASA Collaboration reported that the production cross section of the pn→dπ0π0 reaction shows evidence of an isoscalar Jp=1+or 3+ subthreshold△△resonance with mass～2.36 GeV and width～80 MeV, stimulates the research further. Besides, the recent experiments of BABAR. Belle, BES, CLEO, DO and CDF collaborations reported a lot of new hadron states, which are difficult to fit into the conventional hadron pictures (meson: qq, baryon:q3). Various theoretical explanations, include tetraquark states and molecular states, are proposed. The further experiments at COSY, JLab, BEPCII, SPRING-8, COMPAS and other facilities will provide more information on exotic hadrons, especially with the available of strange hadron beams, J-PARC will be a good place to do hyperon-nucleon (YN) scattering to search strange dibaryons.Quantum chromodynamics (QCD) has been verified to be the fundamental theory of the strong interaction in the perturbative region. However, in the low energy region, it is hard to directly use QCD to study the complicated systems such as hadron-hadron interactions and exotic quark states due to the non-perturbative nature. Recently lattice QCD has achieved a lot of successes in hadron spectrum and has also made impressive progresses on nucleon-nucleon (NN) interactions and tetra-and penta-quark systems, it is still far from satisfactory. Therefore, various QCD-inspired models have been developed and used to get physical insights of many phenomena of the hadronic world. The most convenient and widely used approach is the constituent quark model. The typical one is the chiral quark model(ChQM).In ChQM, the constituent quarks interact with each other through Goldstone bosons exchange in addition to the effective one-gluon-exchange. To obtain the immediate-range attraction, theσmeson has to be introduced. BES and other collaborations has observed a signal inππinvariant mass spectra. But the modern treatments of correlated two-pion exchange show that in addition to a long-range scalar-isoscalar attraction traditionally associated with scalar exchange, there is also a strong scalar-isoscalar repulsive core, a complication that has not yet been included in theσexchange.An alternative approach to study baryon-baryon interaction is quark delocalization color screening model (QDCSM), which was developed in 1990s with the aim of explaining the similarities between nuclear and molecular forces. By introducing the quark delocal-ization to enlarge the model space and taking into account of the differences of confinement interaction inside a single baryon and between two color singlet baryons, the model give a good description of N N, Y N interactions and the properties of deuteron. Recent studies also show that the intermediate-range attraction mechanism in QDCSM, quark delocal-ization and color screening is an alternative mechanism other than theσ-meson exchange in ChQM.Because of the unique color structure of the conventional hadron, the construction of quark model for hadrons is easy and effective. However it also limits us to obtain more information about color structure of QCD. To explore the abundant color structure of QCD, the study of multiquark system is necessary. There have been a lot of study on the non-strange dibaryon. The present work is concentrated on the dibaryon with strangeness. First a systematic search of dibaryon with strangeness is done to find the possible dibaryon candidates. Secondly to provide the necessary information for experiments to search for the dibaryon states, the calculation of baryon-baryon scattering, the main production process of dibaryon, is indispensable. The scattering phase shifts will show a resonance behavior in the dibaryon resonance energy region. The NN scattering phase shifts in-cluding N△and△△channel couplings in the framework of resonating-group method (RGM) have been calculated recently by our group. The resonances appeared in NN 3S1, 3D3 and 1D2 scattering phase shifts, and the first two can be used to explain the experi-mental data on ABC effect of CELSIUS-WASA Collaboration. Extending the calculation to strange sector is the goal of the present work. As before, two quark models, ChQM and QDCSM, are used for mutual check. However the application of the RGM formalism to the baryon-baryon system with strangeness is not actually straightforward. In RGM, the reduced mass of two cluster is obtained by separating the total kinetic energy of six quarks into internal part, relative motion part and center-of-mass part. Here we come across the problem that the inertia mass of the strange baryon is not properly reproduced in any kind of the quark models. For N N scattering, the theoretical reduced mass is the same as the experimental one. For strange baryons, the theoretical reduced masses are different from the experimental ones. To ensure the correct scattering kinematics, the reduced mass employed in the RGM equation should be, therefore, readjusted to the experimental value. Two prescriptions to do this without breaking the Pauli principle is used.There are two parts in the present work:1. A systematic search of dibaryon candidates with strangeness (S=-1 to S=-6) in the framework of bound state calculation is done by using QDCSM and ChQM (Salamenca version). Several dibaryon candidates are proposed. The results also show again the two models are almost equivalent, they give almost the same dibaryon candidates here, The difference is only that the binding energies are different in the two models.2. Baryon-baryon scattering phase shifts are studied by means of RGM. The results show that all the dibaryon candidates proposed in the systematic search all appear as resonances in the corresponding baryon-baryon scattering phase shifts. The resonance energies are a little smaller than the corresponding energies in the bound state calcula-tion. In our calculation, we found an interesting phenomenon:For a fixed bound state, coupled to different baryon-baryon scattering channels give almost the same resonance energy. If there are several bound states with the same quantum numbers, generally only one complete resonance, corresponds to the lowest state, appears in the corresponding baryon-baryon scattering phase shifts, Other states are pushed up above their thresholds due to the channel coupling, except the interaction between these states are very weak. It is a very interesting feature and worth further study. There are several general features in calculation. No bound state appears in the octet-octet channels and several resonances exist in the octet-decuplet and decuplet-decuplet channels. These resonances distributed in the energy region 2400-2800 MeV. The widths are generally smaller than ten MeV, but increased to tens of MeV after taking into account the off shell widths of decuplet baryons. These resonances all appear in the D-wave nucleon-hyperon and hyperon-hyperon scat-terings and can be searched through hyperon-nucleon scatterings with the strange hadron beams in J-PARC and hyperon-hyperon vertex and masses reconstruction with the data collected by relativistic heavy ion collisions. The possible dibaryon candidates are:1) SIJ=-1,1/2,3 with mass of 2440-2540 MeV and a width of 48-118 MeV can be searched through NΛ,NΣscattering；2)SIJ=-2,0,2 with mass of 2400-2430 MeV and width of 10-11 MeV and SIJ=-2,1,3,with a mass of 2620-2660 MeV and with of 50-90 MeV can be searched through NΞscattering;3)SIJ=-3.1/2.2 with mass of 2528-2547 MeV and width of 2-4 MeV can be identified throughΛΞmass vertex reconstruction; and 4)SIJ=一3,3/2,3 with mass of 2788-2795 MeV and width of 50-60 MeV can be identified throughΣΞvertex mass reconstruction. |
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