Λ(1405) from Lattice QCD(Exotic Hadrons,New Frontiers in QCD 2010-Exotic Hadron Systems and Dense Matter-)

概要

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Low-lying Λ 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 2×2 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 β's, β=1.80, 1.95 and 2.10, whose corresponding lattice spacings are a=0.2150, 0.1555 and 0.1076fm. For each cutoff, we adopt four different hopping parameters, (κ_<val>, κ_<sea>). The corresponding pion masses range from about 500MeV to 1.1GeV. The results are extrapolated to the physical quark-mass point. Our results indicate that there are two negative-parity Λ states nearly degenerate at around 1.6GeV, whereas no state as low as Λ(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.
2010-12-17