String Junction Model, Cluster Hypothesis, Penta-Quark Baryon and Tetra-Quark Meson(Nuclear Physics)

概要

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Thirty years ago we proposed string junction model of hadrons and examined structure and reaction of hadrons including exotic ones. Mass m of exotic hadrons of light quarks is roughly given by m〜N_J・m_B, where N_J is the total number of junctions and m_B〜1GeV is the ordinary light baryon mass. In this paper we introduce "cluster hypothesis" into the model by which mass of a complex hadron is given by the sum of masses of clusters composing it. The hypothesis guarantees the established picture that mass differences of hadrons of the same string junction structure are due to those of the constituent quarks. A candidate for penta-quark baryon Θ(1530MeV,S=+1) including a strange anti-quark s^^- and that for tetra-quark meson Z^+(4430MeV) recently reported by the Belle collaboration are examined in parallel. Θ is considered to have non-strange partners, which are lighter by the mass difference Δ_s between strange and non-strange quarks. Mass of such light penta-quark baryons with N_J=3 is expected to be about 3GeV. Several parameters of the model are estimated such as mass of junction of m_J〜O(10)MeV. While mass of light tetra-quark meson with N_J=2 is expected to be about 2GeV, Z^+(4430MeV) containing (u,c,d^^-,c^^-) gives a clue to determine some parameters of the model, e.g., inter-junction string energy m_<IJ>.
理論物理学刊行会の論文
2008-10-25