$\Lambda (1405)$ from lattice QCD

Abstract

Low-lying $\Lambda$ 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 $2\times 2$ 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 $\mathcal{O}(a)$-improved quark action. Simulation 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, (${\kappa }_{\mathrm{val}},{\kappa }_{\mathrm{sea}}$). 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.

Proceedings of a talk given at "New Frontiers in QCD 2010 (NFQCD10)", Kyoto, Japan, 18 January to 19 March, 2010

References in corpus (3)

• Quark mass dependence of the rho and sigma from dispersion relations and Chiral Perturbation Theory
• Excited hadrons on the lattice: Baryons
• Excited State Nucleon Spectrum with Two Flavors of Dynamical Fermions