Branching ratio change in K- absorption at rest and the nature of the Lambda(1405)

We investigate in-medium corrections to the branching ratio in K- absorption at rest and their effect on the (positively and negatively) charged pion spectrum. The in-medium corrections are due to Pauli blocking, which arises if the Lambda(1405) is assumed to be a $\bar{K}$-nucleon bound state and leads to a density and momentum dependent mass shift of the Lambda(1405). Requiring that the optical potential as well as the branching ratio are derived from the same elementary T-matrix, we find that the in-medium corrected, density dependent T-matrix gives a better description of the K- absorption reaction than the free, density-independent one. This result suggests that the dominant component of the Lambda(1405) wave function is the $\bar{K}N$ bound state.Comment: 8 Pages, Revtex with epsf, and embedded 8 ps figure

Spin-Orbit Force of Instanton-Induced Interaction in Strange and Charmed Systems

Effects of the spin orbit-force on hadronic systems with strangeness or charm are investigated by a valence quark model with the instanton-induced interaction. By introducing this interaction, the spin-orbit splittings in the negative-parity hyperons becomes 0.14 -- 0.37 times smaller. The flavor-octet baryon mass spectrum and the splittings in the charmed baryons become consistent with the experiments. Though the splitting is also reduced in the flavor-singlet baryons, it still gives two third of the experimental value. The reduction comes from the cancellation between the one-gluon exchange and the instanton-induced interaction, which is channel-specific. In most of the two-baryon channels, the symmetric and antisymmetric spin-orbit force of the YN interaction remains strong after introducing this instanton effect. A few exceptional channels, however, are found where the cancellation affects strongly and the spin-orbit force becomes small.Comment: 22 pages & 2 figure