Search for the possible S = +1 pentaquark states in quenched lattice QCD -: art. no. 114509

We study spin 1/2 hadronic states in quenched lattice QCD to search for a possible S=+1 pentaquark resonance. Simulations are carried out on 8(3)x24, 10(3)x24, 12(3)x24, and 16(3)x24 lattices at beta=5.7 at the quenched level with the standard plaquette gauge action and the Wilson quark action. We adopt a Dirichlet boundary condition in the time direction for the quark to circumvent the possible contaminations due to the (anti)periodic boundary condition for the quark field, which are peculiar to the pentaquark. By diagonalizing the 2x2 correlation matrices constructed from two independent operators with the quantum numbers (I,J)=(0, 1/2), we successfully obtain the energies of the lowest state and the 2nd-lowest state in this channel. The analysis of the volume dependence of the energies and spectral weight factors indicates that a resonance state is likely to exist slightly above the nucleon-Kaon (NK) threshold in (I,J(P))=(0, 1/2(-)) channel.