Four- And five-body scattering calculations of exotic hadron systems

We study the five-quark system uudds̄ in the standard non-relativistic quark model by solving the scattering problem. Using the Gaussian Expansion Method (GEM), we perform the almost precise multi-quark calculations by treating a very large five-body modelspace including the NK scattering channel explicitly. Although a lot of pseudostates (discretized continuum states) with J^π = 1/2^± and J^π = 3/2 ^± are obtained within the bound-state approximation, all the states in 1.4 - 1.85 GeV in mass around Θ⁺(1540) melt into non-resonant continuum states through the coupling with the NK scattering state in the realistic case, i.e., there is no five-quark resonance below 1.85 GeV. Instead, we predict a five-quark resonance state of J^π = 1/2 ^- with the mass of about 1.9 GeV and the width of Γ ≃ 2.68 MeV. Similar calculation is done for the four-quark system cc̄qq̄ (q = u, d) in connection with X⁰ (3872).