Mass Spectra of Pentaquarks -- Overlap versus Wilson Fermions

We investigate the mass spectra of $\Theta^+(udud\bar s)$ in quenched lattice QCD, with overlap and Wilson fermions respectively. Using three different interpolating operators, we measure their correlation matrix, and extract the mass spectra in even and odd parity channels, for 100 gauge configurations generated with single plaquette action at $\beta=6.1$ on the $20^3 \times 40$ lattice. The lowest $ 1/2^- $ state agrees with the $ KN $ s-wave scattering state, for both fermion schemes. On the other hand, for the lowest $ 1/2^+ $ state, it is different from any hadron scattering states for the overlap fermion, while it seems to agree with $ KN^* $ s-wave for the Wilson fermion.