Λ(1405) from Lattice QCD

Low-lying A baryons with spin 1/2 are analyzed in two-flavor lattice QCD. In order to extract two low-lying states for each parity, we construct 2 x 2 cross correlators from flavor SU(3) "octet" and "singlet" baryon operators, and diagonalize them. Two-flavor CP-PACS gauge configurations are employed, which are generated with the renormalization-group improved gauge action and the O(a)-improved quark action. Simulations are performed at three different beta's, beta = 1.80, 1.95 and 2.10, whose corresponding lattice spacings are a = 0.2150, 0.1555 and 0.1076 fm. For each cutoff, we adopt four different hopping parameters, (kappa(val), kappa(sea)). The corresponding pion masses range from about 500 MeV to 1.1 GeV. The results are extrapolated to the physical quark-mass point. Our results indicate that there are two negative-parity Lambda states nearly degenerate at around 1.6 GeV, whereas no state as low as Lambda(1405) is observed. By extracting the flavor components of each state, we find that the lowest (1st-excited) negative-parity state is dominated by flavor-singlet (flavor-octet) component.