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

The A(Kstop−,π±Σ∓)A′A(K^-_{stop},\pi^\pm\Sigma^\mp)A' reaction on p-shell nuclei

This letter is concerned with the study of the $K^-_{stop}A\rightarrow \pi^\pm\Sigma^\mp A'$ reaction in p-shell nuclei, i.e., $^{6,7}Li$, $^9Be$, $^{13}C$ and $^{16}O$. The $\pi^\pm\Sigma^\mp / K^-_{stop}$ emission rates are reported as a function of $A$. These rates are discussed in comparison with previous findings. The ratio $\pi^-\Sigma^+/\pi^+\Sigma^-$ in p-shell nuclei is found to depart largely from that on hydrogen, which provides support for large in-medium effects possibly generated by the sub-threshold $\Lambda(1405)$. The continuum momentum spectra of prompt pions and free sigmas are also discussed as well as the $\pi^\pm\Sigma^\mp$ missing mass behavior and the link with the reaction mechanism. The apparatus used for the investigation is the FINUDA spectrometer operating at the DA$\Phi$NE $\phi$-factory (LNF-INFN, Italy).Comment: 14 pages, 5 figures, accepted for publication in Phys. Lett.