Signal of Theta^+ in quenched lattice QCD with exact chiral symmetry

Abstract

We investigate the mass spectrum of the pentaquark baryon ($udud\bar{s}$) in quenched lattice QCD with exact chiral symmetry. Using 3 different interpolating operators, we measure their $3\times 3$ correlation matrix and obtain the eigenvalues $A^{\pm }(t)$ with $\pm$ parity, for 100 gauge configurations generated with Wilson gauge action at $\beta =6.1$ on the $20^3\times 40$ lattice. For the lowest-lying $J^P=1/2^{-}$ state, its effective mass is almost identical to that of the KN s-wave, while for the lowest-lying $J^P=1/2^{+}$ state, its effective mass is smaller than that of the KN p-wave, especially for the regime $m_u<m_s$. By chiral extrapolation (linear in $m_{\pi }^2$) to $m_{\pi }=135$ MeV, we obatin the masses of the lowest-lying states: $m(1/2^{-})=1424(57)$ MeV and $m(1/2^{+})=1562(121)$ MeV, in agreement with the masses of $m_K+m_N\simeq 1430$ MeV and ${\Theta }^{+}(1540)$ respectively.

Comments: 8 pages, 3 figures, to appear in the Proceedings of PENTAQUARK 2004, SPring8, Japan, July 20-23, 2004