Lattice QCD Study of the Pentaquark Baryons

We study the spin 1/2 hadronic state in quenched lattice QCD to search for a possible S = +1 pentaquark resonance. Simulations are carried out on 8³ × 24, 10³ × 24, 12³ × 24 and 16³ × 24 lattices at β=5.7 at the quenched level with the standard plaquette gauge action and Wilson quark action. We adopt two independent operators with I = 0 and J^P = 1/2 to construct a 2 × 2 correlation matrix. After the diagonalization of the correlation matrix, we successfully obtain the energies of the ground-state and the 1st excited-state in this channel. The volume dependence of the energies suggests the existence of a possible resonance state slightly above the NK threshold in I = 0 and J^P = 1/2^- channel.