The A(K(stop)(-), pi(+/-)Sigma(-/+))A ' reaction on p-shell nuclei

This Letter is concerned with the study of the K− 1316±∓−stop A → π±Σ∓ A′ reaction in p-shell nuclei, i.e., 6,7Li, 9Be, C and O. The π Σ /Kstop emission rates are reported as a function of A. These rates are discussed in comparison with previous findings. The ratio π − Σ + /π + Σ − 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 Λ(1405). The continuum momentum spectra of prompt pions and free sigmas are also discussed as well as the π±Σ∓ missing mass behavior and the link with the reaction mechanism. The apparatus used for the investigation is the FINUDA spectrometer operating at the DANE φ-factory (LNF- INFN, Italy).